Merge branch 'diff-line-comment-vuejs' into 'master'

Diff line comments resolve

## What does this MR do?

Diff line comments can be resolved.

Part of #10325 

To do:

- [x] Backend (@DouweM)
  - [x] Fix https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5022#note_13319326. Will be made easier by https://gitlab.com/gitlab-org/gitlab-ce/issues/17237#note_13370331
  - [x] System note when all discussions are resolved
  - [x] Notification when all discussions are resolved
  - [x] Write unit tests
  - [x] Look at resolve time https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5022#note_13912743 - Fixed by 4a13aa9
- [x] Frontend (@iamphill)
  - [x] Fix bugs
  - [x] Write more feature tests 
- [x] Frontend (@connorshea)
  - [x] Address frontend feedback
  - [x] Feature specs for Jump feature
  - [x] Documentation
  - [x] Add Vue.js in a standard way

See merge request !5022

76 files changed, 3629 insertions, 137 deletions

diff --git a/CHANGELOG b/CHANGELOG
index 98638b8eb28..7ea2631f9f4 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -30,6 +30,7 @@ v 8.11.0 (unreleased)
   - Expand commit message width in repo view (ClemMakesApps)
   - Cache highlighted diff lines for merge requests
   - Pre-create all builds for a Pipeline when the new Pipeline is created !5295
+  - Allow merge request diff notes and discussions to be explicitly marked as resolved
   - API: Add deployment endpoints
   - API: Add Play endpoint on Builds
   - Fix of 'Commits being passed to custom hooks are already reachable when using the UI'
diff --git a/app/assets/javascripts/application.js b/app/assets/javascripts/application.js
index f6e8e770527..a122fa2d637 100644
--- a/app/assets/javascripts/application.js
+++ b/app/assets/javascripts/application.js
@@ -225,10 +225,13 @@
     });
     $body.on("click", ".js-toggle-diff-comments", function(e) {
       var $this = $(this);
-      var showComments = $this.hasClass('active');
-
       $this.toggleClass('active');
-      $this.closest(".diff-file").find(".notes_holder").toggle(showComments);
+      var notesHolders = $this.closest('.diff-file').find('.notes_holder');
+      if ($this.hasClass('active')) {
+        notesHolders.show();
+      } else {
+        notesHolders.hide();
+      }
       return e.preventDefault();
     });
     $document.off("click", '.js-confirm-danger');
diff --git a/app/assets/javascripts/diff_notes/components/comment_resolve_btn.js.es6 b/app/assets/javascripts/diff_notes/components/comment_resolve_btn.js.es6
new file mode 100644
index 00000000000..48bc7d77805
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/components/comment_resolve_btn.js.es6
@@ -0,0 +1,49 @@
+((w) => {
+  w.CommentAndResolveBtn = Vue.extend({
+    props: {
+      discussionId: String,
+      textareaIsEmpty: Boolean
+    },
+    computed: {
+      discussion: function () {
+        return CommentsStore.state[this.discussionId];
+      },
+      showButton: function () {
+        if (this.discussion) {
+          return this.discussion.isResolvable();
+        } else {
+          return false;
+        }
+      },
+      isDiscussionResolved: function () {
+        return this.discussion.isResolved();
+      },
+      buttonText: function () {
+        if (this.isDiscussionResolved) {
+          if (this.textareaIsEmpty) {
+            return "Unresolve discussion";
+          } else {
+            return "Comment & unresolve discussion";
+          }
+        } else {
+          if (this.textareaIsEmpty) {
+            return "Resolve discussion";
+          } else {
+            return "Comment & resolve discussion";
+          }
+        }
+      }
+    },
+    ready: function () {
+      const $textarea = $(`#new-discussion-note-form-${this.discussionId} .note-textarea`);
+      this.textareaIsEmpty = $textarea.val() === '';
+
+      $textarea.on('input.comment-and-resolve-btn', () => {
+        this.textareaIsEmpty = $textarea.val() === '';
+      });
+    },
+    destroyed: function () {
+      $(`#new-discussion-note-form-${this.discussionId} .note-textarea`).off('input.comment-and-resolve-btn');
+    }
+  });
+})(window);
diff --git a/app/assets/javascripts/diff_notes/components/jump_to_discussion.js.es6 b/app/assets/javascripts/diff_notes/components/jump_to_discussion.js.es6
new file mode 100644
index 00000000000..ad80d1118df
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/components/jump_to_discussion.js.es6
@@ -0,0 +1,188 @@
+(() => {
+  JumpToDiscussion = Vue.extend({
+    mixins: [DiscussionMixins],
+    props: {
+      discussionId: String
+    },
+    data: function () {
+      return {
+        discussions: CommentsStore.state,
+      };
+    },
+    computed: {
+      discussion: function () {
+        return this.discussions[this.discussionId];
+      },
+      allResolved: function () {
+        return this.unresolvedDiscussionCount === 0;
+      },
+      showButton: function () {
+        if (this.discussionId) {
+          if (this.unresolvedDiscussionCount > 1) {
+            return true;
+          } else {
+            return this.discussionId !== this.lastResolvedId;
+          }
+        } else {
+          return this.unresolvedDiscussionCount >= 1;
+        }
+      },
+      lastResolvedId: function () {
+        let lastId;
+        for (const discussionId in this.discussions) {
+          const discussion = this.discussions[discussionId];
+
+          if (!discussion.isResolved()) {
+            lastId = discussion.id;
+          }
+        }
+        return lastId;
+      }
+    },
+    methods: {
+      jumpToNextUnresolvedDiscussion: function () {
+        let discussionsSelector,
+            discussionIdsInScope,
+            firstUnresolvedDiscussionId,
+            nextUnresolvedDiscussionId,
+            activeTab = window.mrTabs.currentAction,
+            hasDiscussionsToJumpTo = true,
+            jumpToFirstDiscussion = !this.discussionId;
+
+        const discussionIdsForElements = function(elements) {
+          return elements.map(function() {
+            return $(this).attr('data-discussion-id');
+          }).toArray();
+        };
+
+        const discussions = this.discussions;
+
+        if (activeTab === 'diffs') {
+          discussionsSelector = '.diffs .notes[data-discussion-id]';
+          discussionIdsInScope = discussionIdsForElements($(discussionsSelector));
+
+          let unresolvedDiscussionCount = 0;
+
+          for (let i = 0; i < discussionIdsInScope.length; i++) {
+            const discussionId = discussionIdsInScope[i];
+            const discussion = discussions[discussionId];
+            if (discussion && !discussion.isResolved()) {
+              unresolvedDiscussionCount++;
+            }
+          }
+
+          if (this.discussionId && !this.discussion.isResolved()) {
+            // If this is the last unresolved discussion on the diffs tab,
+            // there are no discussions to jump to.
+            if (unresolvedDiscussionCount === 1) {
+              hasDiscussionsToJumpTo = false;
+            }
+          } else {
+            // If there are no unresolved discussions on the diffs tab at all,
+            // there are no discussions to jump to.
+            if (unresolvedDiscussionCount === 0) {
+              hasDiscussionsToJumpTo = false;
+            }
+          }
+        } else if (activeTab !== 'notes') {
+          // If we are on the commits or builds tabs,
+          // there are no discussions to jump to.
+          hasDiscussionsToJumpTo = false;
+        }
+
+        if (!hasDiscussionsToJumpTo) {
+          // If there are no discussions to jump to on the current page,
+          // switch to the notes tab and jump to the first disucssion there.
+          window.mrTabs.activateTab('notes');
+          activeTab = 'notes';
+          jumpToFirstDiscussion = true;
+        }
+
+        if (activeTab === 'notes') {
+          discussionsSelector = '.discussion[data-discussion-id]';
+          discussionIdsInScope = discussionIdsForElements($(discussionsSelector));
+        }
+
+        let currentDiscussionFound = false;
+        for (let i = 0; i < discussionIdsInScope.length; i++) {
+          const discussionId = discussionIdsInScope[i];
+          const discussion = discussions[discussionId];
+
+          if (!discussion) {
+            // Discussions for comments on commits in this MR don't have a resolved status.
+            continue;
+          }
+
+          if (!firstUnresolvedDiscussionId && !discussion.isResolved()) {
+            firstUnresolvedDiscussionId = discussionId;
+
+            if (jumpToFirstDiscussion) {
+              break;
+            }
+          }
+
+          if (!jumpToFirstDiscussion) {
+            if (currentDiscussionFound) {
+              if (!discussion.isResolved()) {
+                nextUnresolvedDiscussionId = discussionId;
+                break;
+              }
+              else {
+                continue;
+              }
+            }
+
+            if (discussionId === this.discussionId) {
+              currentDiscussionFound = true;
+            }
+          }
+        }
+
+        nextUnresolvedDiscussionId = nextUnresolvedDiscussionId || firstUnresolvedDiscussionId;
+
+        if (!nextUnresolvedDiscussionId) {
+          return;
+        }
+
+        let $target = $(`${discussionsSelector}[data-discussion-id="${nextUnresolvedDiscussionId}"]`);
+
+        if (activeTab === 'notes') {
+          $target = $target.closest('.note-discussion');
+
+          // If the next discussion is closed, toggle it open.
+          if ($target.find('.js-toggle-content').is(':hidden')) {
+            $target.find('.js-toggle-button i').trigger('click')
+          }
+        } else if (activeTab === 'diffs') {
+          // Resolved discussions are hidden in the diffs tab by default.
+          // If they are marked unresolved on the notes tab, they will still be hidden on the diffs tab.
+          // When jumping between unresolved discussions on the diffs tab, we show them.
+          $target.closest(".content").show();
+
+          $target = $target.closest("tr.notes_holder");
+          $target.show();
+
+          // If we are on the diffs tab, we don't scroll to the discussion itself, but to
+          // 4 diff lines above it: the line the discussion was in response to + 3 context
+          let prevEl;
+          for (let i = 0; i < 4; i++) {
+            prevEl = $target.prev();
+
+            // If the discussion doesn't have 4 lines above it, we'll have to do with fewer.
+            if (!prevEl.hasClass("line_holder")) {
+              break;
+            }
+
+            $target = prevEl;
+          }
+        }
+
+        $.scrollTo($target, {
+          offset: -($('.navbar-gitlab').outerHeight() + $('.layout-nav').outerHeight())
+        });
+      }
+    }
+  });
+
+  Vue.component('jump-to-discussion', JumpToDiscussion);
+})();
diff --git a/app/assets/javascripts/diff_notes/components/resolve_btn.js.es6 b/app/assets/javascripts/diff_notes/components/resolve_btn.js.es6
new file mode 100644
index 00000000000..be6ebc77947
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/components/resolve_btn.js.es6
@@ -0,0 +1,107 @@
+((w) => {
+  w.ResolveBtn = Vue.extend({
+    mixins: [
+      ButtonMixins
+    ],
+    props: {
+      noteId: Number,
+      discussionId: String,
+      resolved: Boolean,
+      namespacePath: String,
+      projectPath: String,
+      canResolve: Boolean,
+      resolvedBy: String
+    },
+    data: function () {
+      return {
+        discussions: CommentsStore.state,
+        loading: false
+      };
+    },
+    watch: {
+      'discussions': {
+        handler: 'updateTooltip',
+        deep: true
+      }
+    },
+    computed: {
+      discussion: function () {
+        return this.discussions[this.discussionId];
+      },
+      note: function () {
+        if (this.discussion) {
+          return this.discussion.getNote(this.noteId);
+        } else {
+          return undefined;
+        }
+      },
+      buttonText: function () {
+        if (this.isResolved) {
+          return `Resolved by ${this.resolvedByName}`;
+        } else if (this.canResolve) {
+          return 'Mark as resolved';
+        } else {
+          return 'Unable to resolve';
+        }
+      },
+      isResolved: function () {
+        if (this.note) {
+          return this.note.resolved;
+        } else {
+          return false;
+        }
+      },
+      resolvedByName: function () {
+        return this.note.resolved_by;
+      },
+    },
+    methods: {
+      updateTooltip: function () {
+        $(this.$els.button)
+          .tooltip('hide')
+          .tooltip('fixTitle');
+      },
+      resolve: function () {
+        if (!this.canResolve) return;
+
+        let promise;
+        this.loading = true;
+
+        if (this.isResolved) {
+          promise = ResolveService
+            .unresolve(this.namespace, this.noteId);
+        } else {
+          promise = ResolveService
+            .resolve(this.namespace, this.noteId);
+        }
+
+        promise.then((response) => {
+          this.loading = false;
+
+          if (response.status === 200) {
+            const data = response.json();
+            const resolved_by = data ? data.resolved_by : null;
+
+            CommentsStore.update(this.discussionId, this.noteId, !this.isResolved, resolved_by);
+            this.discussion.updateHeadline(data);
+          } else {
+            new Flash('An error occurred when trying to resolve a comment. Please try again.', 'alert');
+          }
+
+          this.$nextTick(this.updateTooltip);
+        });
+      }
+    },
+    compiled: function () {
+      $(this.$els.button).tooltip({
+        container: 'body'
+      });
+    },
+    beforeDestroy: function () {
+      CommentsStore.delete(this.discussionId, this.noteId);
+    },
+    created: function () {
+      CommentsStore.create(this.discussionId, this.noteId, this.canResolve, this.resolved, this.resolvedBy);
+    }
+  });
+})(window);
diff --git a/app/assets/javascripts/diff_notes/components/resolve_count.js.es6 b/app/assets/javascripts/diff_notes/components/resolve_count.js.es6
new file mode 100644
index 00000000000..9e383b14a3e
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/components/resolve_count.js.es6
@@ -0,0 +1,18 @@
+((w) => {
+  w.ResolveCount = Vue.extend({
+    mixins: [DiscussionMixins],
+    props: {
+      loggedOut: Boolean
+    },
+    data: function () {
+      return {
+        discussions: CommentsStore.state
+      };
+    },
+    computed: {
+      allResolved: function () {
+        return this.resolvedDiscussionCount === this.discussionCount;
+      }
+    }
+  });
+})(window);
diff --git a/app/assets/javascripts/diff_notes/components/resolve_discussion_btn.js.es6 b/app/assets/javascripts/diff_notes/components/resolve_discussion_btn.js.es6
new file mode 100644
index 00000000000..e373b06b1eb
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/components/resolve_discussion_btn.js.es6
@@ -0,0 +1,60 @@
+((w) => {
+  w.ResolveDiscussionBtn = Vue.extend({
+    mixins: [
+      ButtonMixins
+    ],
+    props: {
+      discussionId: String,
+      mergeRequestId: Number,
+      namespacePath: String,
+      projectPath: String,
+      canResolve: Boolean,
+    },
+    data: function() {
+      return {
+        discussions: CommentsStore.state
+      };
+    },
+    computed: {
+      discussion: function () {
+        return this.discussions[this.discussionId];
+      },
+      showButton: function () {
+        if (this.discussion) {
+          return this.discussion.isResolvable();
+        } else {
+          return false;
+        }
+      },
+      isDiscussionResolved: function () {
+        if (this.discussion) {
+          return this.discussion.isResolved();
+        } else {
+          return false;
+        }
+      },
+      buttonText: function () {
+        if (this.isDiscussionResolved) {
+          return "Unresolve discussion";
+        } else {
+          return "Resolve discussion";
+        }
+      },
+      loading: function () {
+        if (this.discussion) {
+          return this.discussion.loading;
+        } else {
+          return false;
+        }
+      }
+    },
+    methods: {
+      resolve: function () {
+        ResolveService.toggleResolveForDiscussion(this.namespace, this.mergeRequestId, this.discussionId);
+      }
+    },
+    created: function () {
+      CommentsStore.createDiscussion(this.discussionId, this.canResolve);
+    }
+  });
+})(window);
diff --git a/app/assets/javascripts/diff_notes/diff_notes_bundle.js.es6 b/app/assets/javascripts/diff_notes/diff_notes_bundle.js.es6
new file mode 100644
index 00000000000..22d9cf6c857
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/diff_notes_bundle.js.es6
@@ -0,0 +1,35 @@
+//= require vue
+//= require vue-resource
+//= require_directory ./models
+//= require_directory ./stores
+//= require_directory ./services
+//= require_directory ./mixins
+//= require_directory ./components
+
+$(() => {
+  window.DiffNotesApp = new Vue({
+    el: '#diff-notes-app',
+    components: {
+      'resolve-btn': ResolveBtn,
+      'resolve-discussion-btn': ResolveDiscussionBtn,
+      'comment-and-resolve-btn': CommentAndResolveBtn
+    },
+    methods: {
+      compileComponents: function () {
+        const $components = $('resolve-btn, resolve-discussion-btn, jump-to-discussion');
+        if ($components.length) {
+          $components.each(function () {
+            DiffNotesApp.$compile($(this).get(0));
+          });
+        }
+      }
+    }
+  });
+
+  new Vue({
+    el: '#resolve-count-app',
+    components: {
+      'resolve-count': ResolveCount
+    }
+  });
+});
diff --git a/app/assets/javascripts/diff_notes/mixins/discussion.js.es6 b/app/assets/javascripts/diff_notes/mixins/discussion.js.es6
new file mode 100644
index 00000000000..a05f885201d
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/mixins/discussion.js.es6
@@ -0,0 +1,35 @@
+((w) => {
+  w.DiscussionMixins = {
+    computed: {
+      discussionCount: function () {
+        return Object.keys(this.discussions).length;
+      },
+      resolvedDiscussionCount: function () {
+        let resolvedCount = 0;
+
+        for (const discussionId in this.discussions) {
+          const discussion = this.discussions[discussionId];
+
+          if (discussion.isResolved()) {
+            resolvedCount++;
+          }
+        }
+
+        return resolvedCount;
+      },
+      unresolvedDiscussionCount: function () {
+        let unresolvedCount = 0;
+
+        for (const discussionId in this.discussions) {
+          const discussion = this.discussions[discussionId];
+
+          if (!discussion.isResolved()) {
+            unresolvedCount++;
+          }
+        }
+
+        return unresolvedCount;
+      }
+    }
+  };
+})(window);
diff --git a/app/assets/javascripts/diff_notes/mixins/namespace.js.es6 b/app/assets/javascripts/diff_notes/mixins/namespace.js.es6
new file mode 100644
index 00000000000..d278678085b
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/mixins/namespace.js.es6
@@ -0,0 +1,9 @@
+((w) => {
+  w.ButtonMixins = {
+    computed: {
+      namespace: function () {
+        return `${this.namespacePath}/${this.projectPath}`;
+      }
+    }
+  };
+})(window);
diff --git a/app/assets/javascripts/diff_notes/models/discussion.js.es6 b/app/assets/javascripts/diff_notes/models/discussion.js.es6
new file mode 100644
index 00000000000..488714e4870
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/models/discussion.js.es6
@@ -0,0 +1,87 @@
+class DiscussionModel {
+  constructor (discussionId) {
+    this.id = discussionId;
+    this.notes = {};
+    this.loading = false;
+    this.canResolve = false;
+  }
+
+  createNote (noteId, canResolve, resolved, resolved_by) {
+    Vue.set(this.notes, noteId, new NoteModel(this.id, noteId, canResolve, resolved, resolved_by));
+  }
+
+  deleteNote (noteId) {
+    Vue.delete(this.notes, noteId);
+  }
+
+  getNote (noteId) {
+    return this.notes[noteId];
+  }
+
+  notesCount() {
+    return Object.keys(this.notes).length;
+  }
+
+  isResolved () {
+    for (const noteId in this.notes) {
+      const note = this.notes[noteId];
+
+      if (!note.resolved) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  resolveAllNotes (resolved_by) {
+    for (const noteId in this.notes) {
+      const note = this.notes[noteId];
+
+      if (!note.resolved) {
+        note.resolved = true;
+        note.resolved_by = resolved_by;
+      }
+    }
+  }
+
+  unResolveAllNotes () {
+    for (const noteId in this.notes) {
+      const note = this.notes[noteId];
+
+      if (note.resolved) {
+        note.resolved = false;
+        note.resolved_by = null;
+      }
+    }
+  }
+
+  updateHeadline (data) {
+    const $discussionHeadline = $(`.discussion[data-discussion-id="${this.id}"] .js-discussion-headline`);
+
+    if (data.discussion_headline_html) {
+      if ($discussionHeadline.length) {
+        $discussionHeadline.replaceWith(data.discussion_headline_html);
+      } else {
+        $(`.discussion[data-discussion-id="${this.id}"] .discussion-header`).append(data.discussion_headline_html);
+      }
+    } else {
+       $discussionHeadline.remove();
+    }
+  }
+
+  isResolvable () {
+    if (!this.canResolve) {
+      return false;
+    }
+    
+    for (const noteId in this.notes) {
+      const note = this.notes[noteId];
+
+      if (note.canResolve) {
+        return true;
+      }
+    }
+
+    return false;
+  }
+}
diff --git a/app/assets/javascripts/diff_notes/models/note.js.es6 b/app/assets/javascripts/diff_notes/models/note.js.es6
new file mode 100644
index 00000000000..f2d2d389c38
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/models/note.js.es6
@@ -0,0 +1,9 @@
+class NoteModel {
+  constructor (discussionId, noteId, canResolve, resolved, resolved_by) {
+    this.discussionId = discussionId;
+    this.id = noteId;
+    this.canResolve = canResolve;
+    this.resolved = resolved;
+    this.resolved_by = resolved_by;
+  }
+}
diff --git a/app/assets/javascripts/diff_notes/services/resolve.js.es6 b/app/assets/javascripts/diff_notes/services/resolve.js.es6
new file mode 100644
index 00000000000..de771ff814b
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/services/resolve.js.es6
@@ -0,0 +1,88 @@
+((w) => {
+  class ResolveServiceClass {
+    constructor() {
+      this.noteResource = Vue.resource('notes{/noteId}/resolve');
+      this.discussionResource = Vue.resource('merge_requests{/mergeRequestId}/discussions{/discussionId}/resolve');
+    }
+
+    setCSRF() {
+      Vue.http.headers.common['X-CSRF-Token'] = $.rails.csrfToken();
+    }
+
+    prepareRequest(namespace) {
+      this.setCSRF();
+      Vue.http.options.root = `/${namespace}`;
+    }
+
+    resolve(namespace, noteId) {
+      this.prepareRequest(namespace);
+
+      return this.noteResource.save({ noteId }, {});
+    }
+
+    unresolve(namespace, noteId) {
+      this.prepareRequest(namespace);
+
+      return this.noteResource.delete({ noteId }, {});
+    }
+
+    toggleResolveForDiscussion(namespace, mergeRequestId, discussionId) {
+      const discussion = CommentsStore.state[discussionId],
+            isResolved = discussion.isResolved();
+      let promise;
+
+      if (isResolved) {
+        promise = this.unResolveAll(namespace, mergeRequestId, discussionId);
+      } else {
+        promise = this.resolveAll(namespace, mergeRequestId, discussionId);
+      }
+
+      promise.then((response) => {
+        discussion.loading = false;
+
+        if (response.status === 200) {
+          const data = response.json();
+          const resolved_by = data ? data.resolved_by : null;
+
+          if (isResolved) {
+            discussion.unResolveAllNotes();
+          } else {
+            discussion.resolveAllNotes(resolved_by);
+          }
+
+          discussion.updateHeadline(data);
+        } else {
+          new Flash('An error occurred when trying to resolve a discussion. Please try again.', 'alert');
+        }
+      })
+    }
+
+    resolveAll(namespace, mergeRequestId, discussionId) {
+      const discussion = CommentsStore.state[discussionId];
+
+      this.prepareRequest(namespace);
+
+      discussion.loading = true;
+
+      return this.discussionResource.save({
+        mergeRequestId,
+        discussionId
+      }, {});
+    }
+
+    unResolveAll(namespace, mergeRequestId, discussionId) {
+      const discussion = CommentsStore.state[discussionId];
+
+      this.prepareRequest(namespace);
+
+      discussion.loading = true;
+
+      return this.discussionResource.delete({
+        mergeRequestId,
+        discussionId
+      }, {});
+    }
+  }
+
+  w.ResolveService = new ResolveServiceClass();
+})(window);
diff --git a/app/assets/javascripts/diff_notes/stores/comments.js.es6 b/app/assets/javascripts/diff_notes/stores/comments.js.es6
new file mode 100644
index 00000000000..69522e1dac5
--- /dev/null
+++ b/app/assets/javascripts/diff_notes/stores/comments.js.es6
@@ -0,0 +1,53 @@
+((w) => {
+  w.CommentsStore = {
+    state: {},
+    get: function (discussionId, noteId) {
+      return this.state[discussionId].getNote(noteId);
+    },
+    createDiscussion: function (discussionId, canResolve) {
+      let discussion = this.state[discussionId];
+      if (!this.state[discussionId]) {
+        discussion = new DiscussionModel(discussionId);
+        Vue.set(this.state, discussionId, discussion);
+      }
+
+      if (canResolve !== undefined) {
+        discussion.canResolve = canResolve;
+      }
+
+      return discussion;
+    },
+    create: function (discussionId, noteId, canResolve, resolved, resolved_by) {
+      const discussion = this.createDiscussion(discussionId);
+
+      discussion.createNote(noteId, canResolve, resolved, resolved_by);
+    },
+    update: function (discussionId, noteId, resolved, resolved_by) {
+      const discussion = this.state[discussionId];
+      const note = discussion.getNote(noteId);
+      note.resolved = resolved;
+      note.resolved_by = resolved_by;
+    },
+    delete: function (discussionId, noteId) {
+      const discussion = this.state[discussionId];
+      discussion.deleteNote(noteId);
+
+      if (discussion.notesCount() === 0) {
+        Vue.delete(this.state, discussionId);
+      }
+    },
+    unresolvedDiscussionIds: function () {
+      let ids = [];
+
+      for (const discussionId in this.state) {
+        const discussion = this.state[discussionId];
+
+        if (!discussion.isResolved()) {
+          ids.push(discussion.id);
+        }
+      }
+
+      return ids;
+    }
+  };
+})(window);
diff --git a/app/assets/javascripts/merge_request.js b/app/assets/javascripts/merge_request.js
index 47e6dd1084d..56ebf84c4f6 100644
--- a/app/assets/javascripts/merge_request.js
+++ b/app/assets/javascripts/merge_request.js
@@ -34,7 +34,7 @@
 
     MergeRequest.prototype.initTabs = function() {
       if (this.opts.action !== 'new') {
-        return new MergeRequestTabs(this.opts);
+        window.mrTabs = new MergeRequestTabs(this.opts);
       } else {
         return $('.merge-request-tabs a[data-toggle="tab"]:first').tab('show');
       }
diff --git a/app/assets/javascripts/merge_request_tabs.js b/app/assets/javascripts/merge_request_tabs.js
index 4e2273f5aa8..ad08209d61e 100644
--- a/app/assets/javascripts/merge_request_tabs.js
+++ b/app/assets/javascripts/merge_request_tabs.js
@@ -89,6 +89,7 @@
       if (action === 'show') {
         action = 'notes';
       }
+      this.currentAction = action;
       new_state = this._location.pathname.replace(/\/(commits|diffs|builds|pipelines)(\.html)?\/?$/, '');
       if (action !== 'notes') {
         new_state += "/" + action;
@@ -127,6 +128,11 @@
         success: (function(_this) {
           return function(data) {
             $('#diffs').html(data.html);
+
+            if (typeof DiffNotesApp !== 'undefined') {
+              DiffNotesApp.compileComponents();
+            }
+
             gl.utils.localTimeAgo($('.js-timeago', 'div#diffs'));
             $('#diffs .js-syntax-highlight').syntaxHighlight();
             $('#diffs .diff-file').singleFileDiff();
diff --git a/app/assets/javascripts/notes.js b/app/assets/javascripts/notes.js
index 2484a07f363..d0d5cad813a 100644
--- a/app/assets/javascripts/notes.js
+++ b/app/assets/javascripts/notes.js
@@ -68,6 +68,7 @@
       $(document).on("click", ".note-edit-cancel", this.cancelEdit);
       $(document).on("click", ".js-comment-button", this.updateCloseButton);
       $(document).on("keyup input", ".js-note-text", this.updateTargetButtons);
+      $(document).on('click', '.js-comment-resolve-button', this.resolveDiscussion);
       $(document).on("click", ".js-note-delete", this.removeNote);
       $(document).on("click", ".js-note-attachment-delete", this.removeAttachment);
       $(document).on("ajax:complete", ".js-main-target-form", this.reenableTargetFormSubmitButton);
@@ -100,6 +101,7 @@
       $(document).off("click", ".js-note-target-close");
       $(document).off("click", ".js-note-discard");
       $(document).off("keydown", ".js-note-text");
+      $(document).off('click', '.js-comment-resolve-button');
       $('.note .js-task-list-container').taskList('disable');
       return $(document).off('tasklist:changed', '.note .js-task-list-container');
     };
@@ -304,6 +306,11 @@
       } else {
         discussionContainer.append(note_html);
       }
+
+      if (typeof DiffNotesApp !== 'undefined') {
+        DiffNotesApp.compileComponents();
+      }
+
       gl.utils.localTimeAgo($('.js-timeago', note_html), false);
       return this.updateNotesCount(1);
     };
@@ -350,6 +357,7 @@
       form.find("#note_line_code").remove();
       form.find("#note_position").remove();
       form.find("#note_type").remove();
+      form.find('.js-comment-resolve-button').closest('comment-and-resolve-btn').remove();
       return this.parentTimeline = form.parents('.timeline');
     };
 
@@ -393,8 +401,22 @@
      */
 
     Notes.prototype.addDiscussionNote = function(xhr, note, status) {
+      var $form = $(xhr.target);
+
+      if ($form.attr('data-resolve-all') != null) {
+        var namespacePath = $form.attr('data-namespace-path'),
+            projectPath = $form.attr('data-project-path')
+            discussionId = $form.attr('data-discussion-id'),
+            mergeRequestId = $form.attr('data-noteable-iid'),
+            namespace = namespacePath + '/' + projectPath;
+
+        if (ResolveService != null) {
+          ResolveService.toggleResolveForDiscussion(namespace, mergeRequestId, discussionId);
+        }
+      }
+
       this.renderDiscussionNote(note);
-      return this.removeDiscussionNoteForm($(xhr.target));
+      this.removeDiscussionNoteForm($form);
     };
 
 
@@ -411,7 +433,12 @@
       $html.syntaxHighlight();
       $html.find('.js-task-list-container').taskList('enable');
       $note_li = $('.note-row-' + note.id);
-      return $note_li.replaceWith($html);
+
+      $note_li.replaceWith($html);
+
+      if (typeof DiffNotesApp !== 'undefined') {
+        DiffNotesApp.compileComponents();
+      }
     };
 
 
@@ -492,6 +519,15 @@
           var note, notes;
           note = $(el);
           notes = note.closest(".notes");
+
+          if (typeof DiffNotesApp !== "undefined" && DiffNotesApp !== null) {
+            ref = DiffNotesApp.$refs[noteId];
+
+            if (ref) {
+              ref.$destroy(true);
+            }
+          }
+
           if (notes.find(".note").length === 1) {
             notes.closest(".timeline-entry").remove();
             notes.closest("tr").remove();
@@ -530,8 +566,10 @@
       var form, replyLink;
       form = this.formClone.clone();
       replyLink = $(e.target).closest(".js-discussion-reply-button");
-      replyLink.hide();
-      replyLink.after(form);
+      replyLink
+        .closest('.discussion-reply-holder')
+        .hide()
+        .after(form);
       return this.setupDiscussionNoteForm(replyLink, form);
     };
 
@@ -556,9 +594,23 @@
       form.find("#note_noteable_type").val(dataHolder.data("noteableType"));
       form.find("#note_noteable_id").val(dataHolder.data("noteableId"));
       form.find('.js-note-discard').show().removeClass('js-note-discard').addClass('js-close-discussion-note-form').text(form.find('.js-close-discussion-note-form').data('cancel-text'));
+      form.find('.js-note-target-close').remove();
       this.setupNoteForm(form);
+
+      if (typeof DiffNotesApp !== 'undefined') {
+        var $commentBtn = form.find('comment-and-resolve-btn');
+        $commentBtn
+          .attr(':discussion-id', "'" + dataHolder.data('discussionId') + "'");
+        DiffNotesApp.$compile($commentBtn.get(0));
+      }
+
       form.find(".js-note-text").focus();
-      return form.removeClass('js-main-target-form').addClass("discussion-form js-discussion-note-form");
+      form
+        .find('.js-comment-resolve-button')
+        .attr('data-discussion-id', dataHolder.data('discussionId'));
+      form
+        .removeClass('js-main-target-form')
+        .addClass("discussion-form js-discussion-note-form");
     };
 
 
@@ -577,16 +629,19 @@
       nextRow = row.next();
       hasNotes = nextRow.is(".notes_holder");
       addForm = false;
-      targetContent = ".notes_content";
-      rowCssToAdd = "<tr class=\"notes_holder js-temp-notes-holder\"><td class=\"notes_line\" colspan=\"2\"></td><td class=\"notes_content\"></td></tr>";
+      notesContentSelector = ".notes_content";
+      rowCssToAdd = "<tr class=\"notes_holder js-temp-notes-holder\"><td class=\"notes_line\" colspan=\"2\"></td><td class=\"notes_content\"><div class=\"content\"></div></td></tr>";
       if (this.isParallelView()) {
         lineType = $link.data("lineType");
-        targetContent += "." + lineType;
-        rowCssToAdd = "<tr class=\"notes_holder js-temp-notes-holder\"><td class=\"notes_line\"></td><td class=\"notes_content parallel old\"></td><td class=\"notes_line\"></td><td class=\"notes_content parallel new\"></td></tr>";
+        notesContentSelector += "." + lineType;
+        rowCssToAdd = "<tr class=\"notes_holder js-temp-notes-holder\"><td class=\"notes_line old\"></td><td class=\"notes_content parallel old\"><div class=\"content\"></div></td><td class=\"notes_line new\"></td><td class=\"notes_content parallel new\"><div class=\"content\"></div></td></tr>";
       }
+      notesContentSelector += " .content";
       if (hasNotes) {
-        notesContent = nextRow.find(targetContent);
+        nextRow.show();
+        notesContent = nextRow.find(notesContentSelector);
         if (notesContent.length) {
+          notesContent.show();
           replyButton = notesContent.find(".js-discussion-reply-button:visible");
           if (replyButton.length) {
             e.target = replyButton[0];
@@ -600,11 +655,13 @@
         }
       } else {
         row.after(rowCssToAdd);
+        nextRow = row.next();
+        notesContent = nextRow.find(notesContentSelector);
         addForm = true;
       }
       if (addForm) {
         newForm = this.formClone.clone();
-        newForm.appendTo(row.next().find(targetContent));
+        newForm.appendTo(notesContent);
         return this.setupDiscussionNoteForm($link, newForm);
       }
     };
@@ -623,7 +680,9 @@
       glForm = form.data('gl-form');
       glForm.destroy();
       form.find(".js-note-text").data("autosave").reset();
-      form.prev(".js-discussion-reply-button").show();
+      form
+        .prev('.discussion-reply-holder')
+        .show();
       if (row.is(".js-temp-notes-holder")) {
         return row.remove();
       } else {
@@ -732,6 +791,18 @@
       return this.notesCountBadge.text(parseInt(this.notesCountBadge.text()) + updateCount);
     };
 
+    Notes.prototype.resolveDiscussion = function () {
+      var $this = $(this),
+          discussionId = $this.attr('data-discussion-id');
+
+      $this
+        .closest('form')
+        .attr('data-discussion-id', discussionId)
+        .attr('data-resolve-all', 'true')
+        .attr('data-namespace-path', $this.attr('data-namespace-path'))
+        .attr('data-project-path', $this.attr('data-project-path'));
+    };
+
     return Notes;
 
   })();
diff --git a/app/assets/javascripts/single_file_diff.js b/app/assets/javascripts/single_file_diff.js
index b9ae497b0e5..156b9b8abec 100644
--- a/app/assets/javascripts/single_file_diff.js
+++ b/app/assets/javascripts/single_file_diff.js
@@ -35,10 +35,16 @@
       this.isOpen = !this.isOpen;
       if (!this.isOpen && !this.hasError) {
         this.content.hide();
-        return this.collapsedContent.show();
+        this.collapsedContent.show();
+        if (typeof DiffNotesApp !== 'undefined') {
+          DiffNotesApp.compileComponents();
+        }
       } else if (this.content) {
         this.collapsedContent.hide();
-        return this.content.show();
+        this.content.show();
+        if (typeof DiffNotesApp !== 'undefined') {
+          DiffNotesApp.compileComponents();
+        }
       } else {
         return this.getContentHTML();
       }
@@ -57,7 +63,11 @@
             _this.hasError = true;
             _this.content = $(ERROR_HTML);
           }
-          return _this.collapsedContent.after(_this.content);
+          _this.collapsedContent.after(_this.content);
+
+          if (typeof DiffNotesApp !== 'undefined') {
+            DiffNotesApp.compileComponents();
+          }
         };
       })(this));
     };
diff --git a/app/assets/stylesheets/behaviors.scss b/app/assets/stylesheets/behaviors.scss
index a6b9efc49c9..897bc49e7df 100644
--- a/app/assets/stylesheets/behaviors.scss
+++ b/app/assets/stylesheets/behaviors.scss
@@ -21,7 +21,7 @@
   }
 }
 
-
-[v-cloak] {
-  display: none;
+// Hide element if Vue is still working on rendering it fully.
+[v-cloak="true"] {
+  display: none !important;
 }
diff --git a/app/assets/stylesheets/pages/note_form.scss b/app/assets/stylesheets/pages/note_form.scss
index 3784010348a..bd875b9823f 100644
--- a/app/assets/stylesheets/pages/note_form.scss
+++ b/app/assets/stylesheets/pages/note_form.scss
@@ -159,6 +159,32 @@
   }
 }
 
+.discussion-with-resolve-btn {
+  display: table;
+  width: 100%;
+  border-collapse: separate;
+  table-layout: auto;
+
+  .btn-group {
+    display: table-cell;
+    float: none;
+    width: 1%;
+
+    &:first-child {
+      width: 100%;
+      padding-right: 5px;
+    }
+
+    &:last-child {
+      padding-left: 5px;
+    }
+  }
+
+  .btn {
+    width: 100%;
+  }
+}
+
 .discussion-notes-count {
   font-size: 16px;
 }
diff --git a/app/assets/stylesheets/pages/notes.scss b/app/assets/stylesheets/pages/notes.scss
index a2b5437e503..08d1692c888 100644
--- a/app/assets/stylesheets/pages/notes.scss
+++ b/app/assets/stylesheets/pages/notes.scss
@@ -383,3 +383,80 @@ ul.notes {
     color: $gl-link-color;
   }
 }
+
+.line-resolve-all-container {
+  .btn-group {
+    margin-top: -1px;
+    margin-left: -4px;
+  }
+
+  .discussion-next-btn {
+    border-top-left-radius: 0;
+    border-bottom-left-radius: 0;
+  }
+}
+
+.line-resolve-all {
+  display: inline-block;
+  padding: 5px 10px;
+  background-color: $background-color;
+  border: 1px solid $border-color;
+  border-radius: $border-radius-default;
+
+  &.has-next-btn {
+    border-top-right-radius: 0;
+    border-bottom-right-radius: 0;
+  }
+
+  .line-resolve-btn {
+    vertical-align: middle;
+    margin-right: 5px;
+  }
+}
+
+.line-resolve-text {
+  vertical-align: middle;
+}
+
+.line-resolve-btn {
+  display: inline-block;
+  position: relative;
+  top: 2px;
+  padding: 0;
+  background-color: transparent;
+  border: none;
+  outline: 0;
+
+  &.is-disabled {
+    cursor: default;
+  }
+
+  &:not(.is-disabled):hover,
+  &:not(.is-disabled):focus,
+  &.is-active {
+    color: $gl-text-green;
+
+    svg path {
+      fill: $gl-text-green;
+    }
+  }
+
+  svg {
+    position: relative;
+    color: $notes-action-color;
+
+    path {
+      fill: $notes-action-color;
+    }
+  }
+}
+
+.discussion-next-btn {
+  svg {
+    margin: 0;
+    
+    path {
+      fill: $gray-darkest;
+    }
+  }
+}
diff --git a/app/controllers/projects/discussions_controller.rb b/app/controllers/projects/discussions_controller.rb
new file mode 100644
index 00000000000..b2e8733ccb7
--- /dev/null
+++ b/app/controllers/projects/discussions_controller.rb
@@ -0,0 +1,43 @@
+class Projects::DiscussionsController < Projects::ApplicationController
+  before_action :module_enabled
+  before_action :merge_request
+  before_action :discussion
+  before_action :authorize_resolve_discussion!
+
+  def resolve
+    discussion.resolve!(current_user)
+
+    MergeRequests::ResolvedDiscussionNotificationService.new(project, current_user).execute(merge_request)
+
+    render json: {
+      resolved_by: discussion.resolved_by.try(:name),
+      discussion_headline_html: view_to_html_string('discussions/_headline', discussion: discussion)
+    }
+  end
+
+  def unresolve
+    discussion.unresolve!
+
+    render json: {
+      discussion_headline_html: view_to_html_string('discussions/_headline', discussion: discussion)
+    }
+  end
+
+  private
+
+  def merge_request
+    @merge_request ||= @project.merge_requests.find_by!(iid: params[:merge_request_id])
+  end
+
+  def discussion
+    @discussion ||= @merge_request.find_diff_discussion(params[:id]) || render_404
+  end
+
+  def authorize_resolve_discussion!
+    access_denied! unless discussion.can_resolve?(current_user)
+  end
+
+  def module_enabled
+    render_404 unless @project.merge_requests_enabled
+  end
+end
diff --git a/app/controllers/projects/merge_requests_controller.rb b/app/controllers/projects/merge_requests_controller.rb
index 0f52a5f96a3..d3fe441c4d2 100644
--- a/app/controllers/projects/merge_requests_controller.rb
+++ b/app/controllers/projects/merge_requests_controller.rb
@@ -435,12 +435,9 @@ class Projects::MergeRequestsController < Projects::ApplicationController
   # :show, :diff, :commits, :builds. but not when request the data through AJAX
   def define_discussion_vars
     # Build a note object for comment form
-    @note = @project.notes.new(noteable: @noteable)
+    @note = @project.notes.new(noteable: @merge_request)
 
-    @discussions = @noteable.mr_and_commit_notes.
-      inc_author_project_award_emoji.
-      fresh.
-      discussions
+    @discussions = @merge_request.discussions
 
     preload_noteable_for_regular_notes(@discussions.flat_map(&:notes))
 
@@ -474,7 +471,7 @@ class Projects::MergeRequestsController < Projects::ApplicationController
     }
 
     @use_legacy_diff_notes = !@merge_request.has_complete_diff_refs?
-    @grouped_diff_discussions = @merge_request.notes.inc_author_project_award_emoji.grouped_diff_discussions
+    @grouped_diff_discussions = @merge_request.notes.inc_relations_for_view.grouped_diff_discussions
 
     Banzai::NoteRenderer.render(
       @grouped_diff_discussions.values.flat_map(&:notes),
diff --git a/app/controllers/projects/notes_controller.rb b/app/controllers/projects/notes_controller.rb
index f2422729364..0948ad21649 100644
--- a/app/controllers/projects/notes_controller.rb
+++ b/app/controllers/projects/notes_controller.rb
@@ -5,6 +5,7 @@ class Projects::NotesController < Projects::ApplicationController
   before_action :authorize_read_note!
   before_action :authorize_create_note!, only: [:create]
   before_action :authorize_admin_note!, only: [:update, :destroy]
+  before_action :authorize_resolve_note!, only: [:resolve, :unresolve]
   before_action :find_current_user_notes, only: [:index]
 
   def index
@@ -66,6 +67,33 @@ class Projects::NotesController < Projects::ApplicationController
     end
   end
 
+  def resolve
+    return render_404 unless note.resolvable?
+
+    note.resolve!(current_user)
+
+    MergeRequests::ResolvedDiscussionNotificationService.new(project, current_user).execute(note.noteable)
+
+    discussion = note.discussion
+
+    render json: {
+      resolved_by: note.resolved_by.try(:name),
+      discussion_headline_html: (view_to_html_string('discussions/_headline', discussion: discussion) if discussion)
+    }
+  end
+
+  def unresolve
+    return render_404 unless note.resolvable?
+
+    note.unresolve!
+
+    discussion = note.discussion
+
+    render json: {
+      discussion_headline_html: (view_to_html_string('discussions/_headline', discussion: discussion) if discussion)
+    }
+  end
+
   private
 
   def note
@@ -138,7 +166,7 @@ class Projects::NotesController < Projects::ApplicationController
       }
 
       if note.diff_note?
-        discussion = Discussion.new([note])
+        discussion = note.to_discussion
 
         attrs.merge!(
           diff_discussion_html: diff_discussion_html(discussion),
@@ -175,6 +203,10 @@ class Projects::NotesController < Projects::ApplicationController
     return access_denied! unless can?(current_user, :admin_note, note)
   end
 
+  def authorize_resolve_note!
+    return access_denied! unless can?(current_user, :resolve_note, note)
+  end
+
   def note_params
     params.require(:note).permit(
       :note, :noteable, :noteable_id, :noteable_type, :project_id,
diff --git a/app/helpers/appearances_helper.rb b/app/helpers/appearances_helper.rb
index e12a1052988..de13e7a1fc2 100644
--- a/app/helpers/appearances_helper.rb
+++ b/app/helpers/appearances_helper.rb
@@ -32,6 +32,8 @@ module AppearancesHelper
   end
 
   def custom_icon(icon_name, size: 16)
+    # We can't simply do the below, because there are some .erb SVGs.
+    #  File.read(Rails.root.join("app/views/shared/icons/_#{icon_name}.svg")).html_safe
     render "shared/icons/#{icon_name}.svg", size: size
   end
 end
diff --git a/app/helpers/notes_helper.rb b/app/helpers/notes_helper.rb
index 26bde2230a9..da230f76bae 100644
--- a/app/helpers/notes_helper.rb
+++ b/app/helpers/notes_helper.rb
@@ -49,7 +49,7 @@ module NotesHelper
     }
 
     if use_legacy_diff_note
-      discussion_id = LegacyDiffNote.build_discussion_id(
+      discussion_id = LegacyDiffNote.discussion_id(
         @comments_target[:noteable_type],
         @comments_target[:noteable_id] || @comments_target[:commit_id],
         line_code
@@ -60,7 +60,7 @@ module NotesHelper
         discussion_id: discussion_id
       )
     else
-      discussion_id = DiffNote.build_discussion_id(
+      discussion_id = DiffNote.discussion_id(
         @comments_target[:noteable_type],
         @comments_target[:noteable_id] || @comments_target[:commit_id],
         position
@@ -81,10 +81,8 @@ module NotesHelper
 
     data = discussion.reply_attributes.merge(line_type: line_type)
 
-    content_tag(:div, class: "discussion-reply-holder") do
-      button_tag 'Reply...', class: 'btn btn-text-field js-discussion-reply-button',
-                             data: data, title: 'Add a reply'
-    end
+    button_tag 'Reply...', class: 'btn btn-text-field js-discussion-reply-button',
+                           data: data, title: 'Add a reply'
   end
 
   def preload_max_access_for_authors(notes, project)
diff --git a/app/mailers/emails/merge_requests.rb b/app/mailers/emails/merge_requests.rb
index 95810b0ac6e..ec27ac517db 100644
--- a/app/mailers/emails/merge_requests.rb
+++ b/app/mailers/emails/merge_requests.rb
@@ -47,6 +47,13 @@ module Emails
       mail_answer_thread(@merge_request, merge_request_thread_options(updated_by_user_id, recipient_id))
     end
 
+    def resolved_all_discussions_email(recipient_id, merge_request_id, resolved_by_user_id)
+      setup_merge_request_mail(merge_request_id, recipient_id)
+
+      @resolved_by = User.find(resolved_by_user_id)
+      mail_answer_thread(@merge_request, merge_request_thread_options(resolved_by_user_id, recipient_id))
+    end
+
     private
 
     def setup_merge_request_mail(merge_request_id, recipient_id)
diff --git a/app/models/ability.rb b/app/models/ability.rb
index 55265c3cfcb..07f703f205d 100644
--- a/app/models/ability.rb
+++ b/app/models/ability.rb
@@ -276,6 +276,7 @@ class Ability
         :create_merge_request,
         :create_wiki,
         :push_code,
+        :resolve_note,
         :create_container_image,
         :update_container_image,
         :create_environment,
@@ -457,7 +458,8 @@ class Ability
         rules += [
           :read_note,
           :update_note,
-          :admin_note
+          :admin_note,
+          :resolve_note
         ]
       end
 
@@ -465,6 +467,10 @@ class Ability
         rules += project_abilities(user, note.project)
       end
 
+      if note.for_merge_request? && note.noteable.author == user
+        rules << :resolve_note
+      end
+
       rules
     end
 
diff --git a/app/models/diff_note.rb b/app/models/diff_note.rb
index e02a3d54c36..f56c3d74ae3 100644
--- a/app/models/diff_note.rb
+++ b/app/models/diff_note.rb
@@ -9,11 +9,13 @@ class DiffNote < Note
   validates :diff_line, presence: true
   validates :line_code, presence: true, line_code: true
   validates :noteable_type, inclusion: { in: ['Commit', 'MergeRequest'] }
+  validates :resolved_by, presence: true, if: :resolved?
   validate :positions_complete
   validate :verify_supported
 
+  after_initialize :ensure_original_discussion_id
   before_validation :set_original_position, :update_position, on: :create
-  before_validation :set_line_code
+  before_validation :set_line_code, :set_original_discussion_id
   after_save :keep_around_commits
 
   class << self
@@ -30,14 +32,6 @@ class DiffNote < Note
     { position: position.to_json }
   end
 
-  def discussion_id
-    @discussion_id ||= self.class.build_discussion_id(noteable_type, noteable_id || commit_id, position)
-  end
-
-  def original_discussion_id
-    @original_discussion_id ||= self.class.build_discussion_id(noteable_type, noteable_id || commit_id, original_position)
-  end
-
   def position=(new_position)
     if new_position.is_a?(String)
       new_position = JSON.parse(new_position) rescue nil
@@ -72,10 +66,48 @@ class DiffNote < Note
     self.position.diff_refs == diff_refs
   end
 
+  def resolvable?
+    !system? && for_merge_request?
+  end
+
+  def resolved?
+    return false unless resolvable?
+
+    self.resolved_at.present?
+  end
+
+  def resolve!(current_user)
+    return unless resolvable?
+    return if resolved?
+
+    self.resolved_at = Time.now
+    self.resolved_by = current_user
+    save!
+  end
+
+  def unresolve!
+    return unless resolvable?
+    return unless resolved?
+
+    self.resolved_at = nil
+    self.resolved_by = nil
+    save!
+  end
+
+  def discussion
+    return unless resolvable?
+
+    self.noteable.find_diff_discussion(self.discussion_id)
+  end
+
+  def to_discussion
+    Discussion.new([self])
+  end
+
   private
 
   def supported?
-    !self.for_merge_request? || self.noteable.has_complete_diff_refs?
+    for_commit? || self.noteable.has_complete_diff_refs?
   end
 
   def noteable_diff_refs
@@ -94,6 +126,26 @@ class DiffNote < Note
     self.line_code = self.position.line_code(self.project.repository)
   end
 
+  def ensure_original_discussion_id
+    return unless self.persisted?
+    return if self.original_discussion_id
+
+    set_original_discussion_id
+    update_column(:original_discussion_id, self.original_discussion_id)
+  end
+
+  def set_original_discussion_id
+    self.original_discussion_id = Digest::SHA1.hexdigest(build_original_discussion_id)
+  end
+
+  def build_discussion_id
+    self.class.build_discussion_id(noteable_type, noteable_id || commit_id, position)
+  end
+
+  def build_original_discussion_id
+    self.class.build_discussion_id(noteable_type, noteable_id || commit_id, original_position)
+  end
+
   def update_position
     return unless supported?
     return if for_commit?
diff --git a/app/models/discussion.rb b/app/models/discussion.rb
index e2218a5f02b..3fddc084af2 100644
--- a/app/models/discussion.rb
+++ b/app/models/discussion.rb
@@ -1,7 +1,7 @@
 class Discussion
   NUMBER_OF_TRUNCATED_DIFF_LINES = 16
 
-  attr_reader :first_note, :notes
+  attr_reader :first_note, :last_note, :notes
 
   delegate  :created_at,
             :project,
@@ -18,6 +18,12 @@ class Discussion
 
             to: :first_note
 
+  delegate  :resolved_at,
+            :resolved_by,
+
+            to: :last_resolved_note,
+            allow_nil: true
+
   delegate :blob, :highlighted_diff_lines, to: :diff_file, allow_nil: true
 
   def self.for_notes(notes)
@@ -30,13 +36,30 @@ class Discussion
 
   def initialize(notes)
     @first_note = notes.first
+    @last_note = notes.last
     @notes = notes
   end
 
+  def last_resolved_note
+    return unless resolved?
+
+    @last_resolved_note ||= resolved_notes.sort_by(&:resolved_at).last
+  end
+
+  def last_updated_at
+    last_note.created_at
+  end
+
+  def last_updated_by
+    last_note.author
+  end
+
   def id
     first_note.discussion_id
   end
 
+  alias_method :to_param, :id
+
   def diff_discussion?
     first_note.diff_note?
   end
@@ -45,6 +68,50 @@ class Discussion
     notes.any?(&:legacy_diff_note?)
   end
 
+  def resolvable?
+    return @resolvable if defined?(@resolvable)
+
+    @resolvable = diff_discussion? && notes.any?(&:resolvable?)
+  end
+
+  def resolved?
+    return @resolved if defined?(@resolved)
+
+    @resolved = resolvable? && notes.none?(&:to_be_resolved?)
+  end
+
+  def resolved_notes
+    notes.select(&:resolved?)
+  end
+
+  def to_be_resolved?
+    resolvable? && !resolved?
+  end
+
+  def can_resolve?(current_user)
+    return false unless current_user
+    return false unless resolvable?
+
+    current_user == self.noteable.author ||
+      current_user.can?(:resolve_note, self.project)
+  end
+
+  def resolve!(current_user)
+    return unless resolvable?
+
+    notes.each do |note|
+      note.resolve!(current_user) if note.resolvable?
+    end
+  end
+
+  def unresolve!
+    return unless resolvable?
+
+    notes.each do |note|
+      note.unresolve! if note.resolvable?
+    end
+  end
+
   def for_target?(target)
     self.noteable == target && !diff_discussion?
   end
@@ -55,8 +122,20 @@ class Discussion
     @active = first_note.active?
   end
 
+  def collapsed?
+    return false unless diff_discussion?
+
+    if resolvable?
+      # New diff discussions only disappear once they are marked resolved
+      resolved?
+    else
+      # Old diff discussions disappear once they become outdated
+      !active?
+    end
+  end
+
   def expanded?
-    !diff_discussion? || active?
+    !collapsed?
   end
 
   def reply_attributes
diff --git a/app/models/legacy_diff_note.rb b/app/models/legacy_diff_note.rb
index 6ed66001513..8e26cbe9835 100644
--- a/app/models/legacy_diff_note.rb
+++ b/app/models/legacy_diff_note.rb
@@ -8,8 +8,8 @@ class LegacyDiffNote < Note
   before_create :set_diff
 
   class << self
-    def build_discussion_id(noteable_type, noteable_id, line_code, active = true)
-      [super(noteable_type, noteable_id), line_code, active].join("-")
+    def build_discussion_id(noteable_type, noteable_id, line_code)
+      [super(noteable_type, noteable_id), line_code].join("-")
     end
   end
 
@@ -21,10 +21,6 @@ class LegacyDiffNote < Note
     { line_code: line_code }
   end
 
-  def discussion_id
-    @discussion_id ||= self.class.build_discussion_id(noteable_type, noteable_id || commit_id, line_code)
-  end
-
   def project_repository
     if RequestStore.active?
       RequestStore.fetch("project:#{project_id}:repository") { self.project.repository }
@@ -119,4 +115,8 @@ class LegacyDiffNote < Note
     diffs = noteable.raw_diffs(Commit.max_diff_options)
     diffs.find { |d| d.new_path == self.diff.new_path }
   end
+
+  def build_discussion_id
+    self.class.build_discussion_id(noteable_type, noteable_id || commit_id, line_code)
+  end
 end
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 4304ef04767..5330a07ee35 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -418,6 +418,32 @@ class MergeRequest < ActiveRecord::Base
     )
   end
 
+  def discussions
+    @discussions ||= self.mr_and_commit_notes.
+      inc_relations_for_view.
+      fresh.
+      discussions
+  end
+
+  def diff_discussions
+    @diff_discussions ||= self.notes.diff_notes.discussions
+  end
+
+  def find_diff_discussion(discussion_id)
+    notes = self.notes.diff_notes.where(discussion_id: discussion_id).fresh.to_a
+    return if notes.empty?
+
+    Discussion.new(notes)
+  end
+
+  def discussions_resolvable?
+    diff_discussions.any?(&:resolvable?)
+  end
+
+  def discussions_resolved?
+    discussions_resolvable? && diff_discussions.none?(&:to_be_resolved?)
+  end
+
   def hook_attrs
     attrs = {
       source: source_project.try(:hook_attrs),
diff --git a/app/models/note.rb b/app/models/note.rb
index ddcd7f9d034..3bbf5db0b70 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -25,6 +25,9 @@ class Note < ActiveRecord::Base
   belongs_to :author, class_name: "User"
   belongs_to :updated_by, class_name: "User"
 
+  # Only used by DiffNote, but defined here so that it can be used in `Note.includes`
+  belongs_to :resolved_by, class_name: "User"
+
   has_many :todos, dependent: :destroy
   has_many :events, as: :target, dependent: :destroy
 
@@ -59,7 +62,7 @@ class Note < ActiveRecord::Base
   scope :fresh, ->{ order(created_at: :asc, id: :asc) }
   scope :inc_author_project, ->{ includes(:project, :author) }
   scope :inc_author, ->{ includes(:author) }
-  scope :inc_author_project_award_emoji, ->{ includes(:project, :author, :award_emoji) }
+  scope :inc_relations_for_view, ->{ includes(:project, :author, :updated_by, :resolved_by, :award_emoji) }
 
   scope :diff_notes, ->{ where(type: ['LegacyDiffNote', 'DiffNote']) }
   scope :non_diff_notes, ->{ where(type: ['Note', nil]) }
@@ -70,7 +73,9 @@ class Note < ActiveRecord::Base
              project: [:project_members, { group: [:group_members] }])
   end
 
+  after_initialize :ensure_discussion_id
   before_validation :nullify_blank_type, :nullify_blank_line_code
+  before_validation :set_discussion_id
   after_save :keep_around_commit
 
   class << self
@@ -82,13 +87,18 @@ class Note < ActiveRecord::Base
       [:discussion, noteable_type.try(:underscore), noteable_id].join("-")
     end
 
+    def discussion_id(*args)
+      Digest::SHA1.hexdigest(build_discussion_id(*args))
+    end
+
     def discussions
       Discussion.for_notes(all)
     end
 
     def grouped_diff_discussions
-      notes = diff_notes.fresh.select(&:active?)
-      Discussion.for_diff_notes(notes).map { |d| [d.line_code, d] }.to_h
+      active_notes = diff_notes.fresh.select(&:active?)
+      Discussion.for_diff_notes(active_notes).
+        map { |d| [d.line_code, d] }.to_h
     end
 
     # Searches for notes matching the given query.
@@ -129,13 +139,16 @@ class Note < ActiveRecord::Base
     true
   end
 
-  def discussion_id
-    @discussion_id ||=
-      if for_merge_request?
-        [:discussion, :note, id].join("-")
-      else
-        self.class.build_discussion_id(noteable_type, noteable_id || commit_id)
-      end
+  def resolvable?
+    false
+  end
+
+  def resolved?
+    false
+  end
+
+  def to_be_resolved?
+    resolvable? && !resolved?
   end
 
   def max_attachment_size
@@ -243,4 +256,26 @@ class Note < ActiveRecord::Base
   def nullify_blank_line_code
     self.line_code = nil if self.line_code.blank?
   end
+
+  def ensure_discussion_id
+    return unless self.persisted?
+    return if self.discussion_id
+
+    set_discussion_id
+    update_column(:discussion_id, self.discussion_id)
+  end
+
+  def set_discussion_id
+    self.discussion_id = Digest::SHA1.hexdigest(build_discussion_id)
+  end
+
+  def build_discussion_id
+    if for_merge_request?
+      # Notes on merge requests are always in a discussion of their own,
+      # so we generate a unique discussion ID.
+      [:discussion, :note, SecureRandom.hex].join("-")
+    else
+      self.class.build_discussion_id(noteable_type, noteable_id || commit_id)
+    end
+  end
 end
diff --git a/app/services/merge_requests/resolved_discussion_notification_service.rb b/app/services/merge_requests/resolved_discussion_notification_service.rb
new file mode 100644
index 00000000000..3a09350c847
--- /dev/null
+++ b/app/services/merge_requests/resolved_discussion_notification_service.rb
@@ -0,0 +1,10 @@
+module MergeRequests
+  class ResolvedDiscussionNotificationService < MergeRequests::BaseService
+    def execute(merge_request)
+      return unless merge_request.discussions_resolved?
+
+      SystemNoteService.resolve_all_discussions(merge_request, project, current_user)
+      notification_service.resolve_all_discussions(merge_request, current_user)
+    end
+  end
+end
diff --git a/app/services/notification_service.rb b/app/services/notification_service.rb
index 2291bc0f127..66a838b3d13 100644
--- a/app/services/notification_service.rb
+++ b/app/services/notification_service.rb
@@ -148,6 +148,14 @@ class NotificationService
     )
   end
 
+  def resolve_all_discussions(merge_request, current_user)
+    recipients = build_recipients(merge_request, merge_request.target_project, current_user, action: "resolve_all_discussions")
+
+    recipients.each do |recipient|
+      mailer.resolved_all_discussions_email(recipient.id, merge_request.id, current_user.id).deliver_later
+    end
+  end
+
   # Notify new user with email after creation
   def new_user(user, token = nil)
     # Don't email omniauth created users
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index e13dc9265b8..546a8f11330 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -158,6 +158,12 @@ module SystemNoteService
     create_note(noteable: noteable, project: project, author: author, note: body)
   end
 
+  def self.resolve_all_discussions(merge_request, project, author)
+    body = "Resolved all discussions"
+
+    create_note(noteable: merge_request, project: project, author: author, note: body)
+  end
+
   # Called when the title of a Noteable is changed
   #
   # noteable  - Noteable object that responds to `title`
diff --git a/app/views/discussions/_diff_discussion.html.haml b/app/views/discussions/_diff_discussion.html.haml
index fa1ad9efa73..1411daeb4a6 100644
--- a/app/views/discussions/_diff_discussion.html.haml
+++ b/app/views/discussions/_diff_discussion.html.haml
@@ -1,6 +1,6 @@
-%tr.notes_holder
+- expanded = local_assigns.fetch(:expanded, true)
+%tr.notes_holder{class: ('hide' unless expanded)}
   %td.notes_line{ colspan: 2 }
   %td.notes_content
-    %ul.notes{ data: { discussion_id: discussion.id } }
-      = render partial: "projects/notes/note", collection: discussion.notes, as: :note
-    = link_to_reply_discussion(discussion)
+    .content
+      = render "discussions/notes", discussion: discussion
diff --git a/app/views/discussions/_diff_with_notes.html.haml b/app/views/discussions/_diff_with_notes.html.haml
index 02b159ffd45..b2e55f7647a 100644
--- a/app/views/discussions/_diff_with_notes.html.haml
+++ b/app/views/discussions/_diff_with_notes.html.haml
@@ -7,8 +7,11 @@
 
   .diff-content.code.js-syntax-highlight
     %table
-      - discussion.truncated_diff_lines.each do |line|
-        = render "projects/diffs/line", line: line, diff_file: diff_file, plain: true
-
-        - if discussion.for_line?(line)
-          = render "discussions/diff_discussion", discussion: discussion
+      - discussions = { discussion.line_code => discussion }
+      = render partial: "projects/diffs/line",
+        collection: discussion.truncated_diff_lines,
+        as: :line,
+        locals: { diff_file: diff_file,
+          discussions: discussions,
+          discussion_expanded: true,
+          plain: true }
diff --git a/app/views/discussions/_discussion.html.haml b/app/views/discussions/_discussion.html.haml
index 49702e048aa..077e8e64e5f 100644
--- a/app/views/discussions/_discussion.html.haml
+++ b/app/views/discussions/_discussion.html.haml
@@ -5,8 +5,17 @@
       = link_to user_path(discussion.author) do
         = image_tag avatar_icon(discussion.author), class: "avatar s40"
     .timeline-content
-      .discussion.js-toggle-container{ class: discussion.id }
+      .discussion.js-toggle-container{ class: discussion.id, data: { discussion_id: discussion.id } }
         .discussion-header
+          .discussion-actions
+            = link_to "#", class: "note-action-button discussion-toggle-button js-toggle-button" do
+              - if expanded
+                = icon("chevron-up")
+              - else
+                = icon("chevron-down")
+
+              Toggle discussion
+
           = link_to_member(@project, discussion.author, avatar: false)
 
           .inline.discussion-headline-light
@@ -29,17 +38,11 @@
 
             = time_ago_with_tooltip(discussion.created_at, placement: "bottom", html_class: "note-created-ago")
 
-          .discussion-actions
-            = link_to "#", class: "note-action-button discussion-toggle-button js-toggle-button" do
-              - if expanded
-                = icon("chevron-up")
-              - else
-                = icon("chevron-down")
-
-              Toggle discussion
+          = render "discussions/headline", discussion: discussion
 
         .discussion-body.js-toggle-content{ class: ("hide" unless expanded) }
           - if discussion.diff_discussion? && discussion.diff_file
             = render "discussions/diff_with_notes", discussion: discussion
           - else
-            = render "discussions/notes", discussion: discussion
+            .panel.panel-default
+              = render "discussions/notes", discussion: discussion
diff --git a/app/views/discussions/_headline.html.haml b/app/views/discussions/_headline.html.haml
new file mode 100644
index 00000000000..c1dabeed387
--- /dev/null
+++ b/app/views/discussions/_headline.html.haml
@@ -0,0 +1,14 @@
+- if discussion.resolved?
+  .discussion-headline-light.js-discussion-headline
+    Resolved
+    - if discussion.resolved_by
+      by
+      = link_to_member(@project, discussion.resolved_by, avatar: false)
+    = time_ago_with_tooltip(discussion.resolved_at, placement: "bottom")
+- elsif discussion.last_updated_at != discussion.created_at
+  .discussion-headline-light.js-discussion-headline
+    Last updated
+    - if discussion.last_updated_by
+      by
+      = link_to_member(@project, discussion.last_updated_by, avatar: false)
+    = time_ago_with_tooltip(discussion.last_updated_at, placement: "bottom")
diff --git a/app/views/discussions/_jump_to_next.html.haml b/app/views/discussions/_jump_to_next.html.haml
new file mode 100644
index 00000000000..69bd416c4de
--- /dev/null
+++ b/app/views/discussions/_jump_to_next.html.haml
@@ -0,0 +1,9 @@
+- discussion = local_assigns.fetch(:discussion, nil)
+- if current_user
+  %jump-to-discussion{ "inline-template" => true, ":discussion-id" => "'#{discussion.try(:id)}'" }
+    .btn-group{ role: "group", "v-show" => "!allResolved", "v-if" => "showButton" }
+      %button.btn.btn-default.discussion-next-btn.has-tooltip{ "@click" => "jumpToNextUnresolvedDiscussion",
+        title: "Jump to next unresolved discussion",
+        "aria-label" => "Jump to next unresolved discussion",
+        data: { container: "body" } }
+        = custom_icon("next_discussion")
diff --git a/app/views/discussions/_notes.html.haml b/app/views/discussions/_notes.html.haml
index a2642b839f6..fbe470bed2c 100644
--- a/app/views/discussions/_notes.html.haml
+++ b/app/views/discussions/_notes.html.haml
@@ -1,5 +1,15 @@
-.panel.panel-default
-  .notes{ data: { discussion_id: discussion.id } }
-    %ul.notes.timeline
-      = render partial: "projects/notes/note", collection: discussion.notes, as: :note
-  = link_to_reply_discussion(discussion)
+%ul.notes{ data: { discussion_id: discussion.id } }
+  = render partial: "projects/notes/note", collection: discussion.notes, as: :note
+
+- if current_user
+  .discussion-reply-holder
+    - if discussion.diff_discussion?
+      - line_type = local_assigns.fetch(:line_type, nil)
+
+      .btn-group-justified.discussion-with-resolve-btn{ role: "group" }
+        .btn-group{ role: "group" }
+          = link_to_reply_discussion(discussion, line_type)
+        = render "discussions/resolve_all", discussion: discussion
+        = render "discussions/jump_to_next", discussion: discussion
+    - else
+      = link_to_reply_discussion(discussion)
diff --git a/app/views/discussions/_parallel_diff_discussion.html.haml b/app/views/discussions/_parallel_diff_discussion.html.haml
index a798c438ea0..f1072ce0feb 100644
--- a/app/views/discussions/_parallel_diff_discussion.html.haml
+++ b/app/views/discussions/_parallel_diff_discussion.html.haml
@@ -1,22 +1,21 @@
-%tr.notes_holder
+- expanded = discussion_left.try(:expanded?) || discussion_right.try(:expanded?)
+%tr.notes_holder{class: ('hide' unless expanded)}
   - if discussion_left
     %td.notes_line.old
     %td.notes_content.parallel.old
-      %ul.notes{ data: { discussion_id: discussion_left.id } }
-        = render partial: "projects/notes/note", collection: discussion_left.notes, as: :note
-
-      = link_to_reply_discussion(discussion_left, 'old')
+      .content{class: ('hide' unless discussion_left.expanded?)}
+        = render "discussions/notes", discussion: discussion_left, line_type: 'old'
   - else
     %td.notes_line.old= ""
-    %td.notes_content.parallel.old= ""
+    %td.notes_content.parallel.old
+      .content
 
   - if discussion_right
     %td.notes_line.new
     %td.notes_content.parallel.new
-      %ul.notes{ data: { discussion_id: discussion_right.id } }
-        = render partial: "projects/notes/note", collection: discussion_right.notes, as: :note
-
-      = link_to_reply_discussion(discussion_right, 'new')
+      .content{class: ('hide' unless discussion_right.expanded?)}
+        = render "discussions/notes", discussion: discussion_right, line_type: 'new'
   - else
     %td.notes_line.new= ""
-    %td.notes_content.parallel.new= ""
+    %td.notes_content.parallel.new
+      .content
diff --git a/app/views/discussions/_resolve_all.html.haml b/app/views/discussions/_resolve_all.html.haml
new file mode 100644
index 00000000000..7a8767ddba0
--- /dev/null
+++ b/app/views/discussions/_resolve_all.html.haml
@@ -0,0 +1,11 @@
+- if discussion.for_merge_request?
+  %resolve-discussion-btn{ ":namespace-path" => "'#{discussion.project.namespace.path}'",
+      ":project-path" => "'#{discussion.project.path}'",
+      ":discussion-id" => "'#{discussion.id}'",
+      ":merge-request-id" => discussion.noteable.iid,
+      ":can-resolve" => discussion.can_resolve?(current_user),
+      "inline-template" => true }
+    .btn-group{ role: "group", "v-if" => "showButton" }
+      %button.btn.btn-default{ type: "button", "@click" => "resolve", ":disabled" => "loading" }
+        = icon("spinner spin", "v-show" => "loading")
+        {{ buttonText }}
diff --git a/app/views/notify/repository_push_email.html.haml b/app/views/notify/repository_push_email.html.haml
index 4dc39a72225..c0c07d65daa 100644
--- a/app/views/notify/repository_push_email.html.haml
+++ b/app/views/notify/repository_push_email.html.haml
@@ -75,8 +75,7 @@
             - blob = diff_file.blob
             - if blob && blob.respond_to?(:text?) && blob_text_viewable?(blob)
               %table.code.white
-                - diff_file.highlighted_diff_lines.each do |line|
-                  = render "projects/diffs/line", line: line, diff_file: diff_file, plain: true, email: true
+                = render partial: "projects/diffs/line", collection: diff_file.highlighted_diff_lines, as: :line, locals: { diff_file: diff_file, plain: true, email: true }
             - else
               No preview for this file type
           %br
diff --git a/app/views/notify/resolved_all_discussions_email.html.haml b/app/views/notify/resolved_all_discussions_email.html.haml
new file mode 100644
index 00000000000..522421b7cc3
--- /dev/null
+++ b/app/views/notify/resolved_all_discussions_email.html.haml
@@ -0,0 +1,2 @@
+%p
+  All discussions on Merge Request #{@merge_request.to_reference} were resolved by #{@resolved_by.name}
diff --git a/app/views/notify/resolved_all_discussions_email.text.erb b/app/views/notify/resolved_all_discussions_email.text.erb
new file mode 100644
index 00000000000..b0d380af8fc
--- /dev/null
+++ b/app/views/notify/resolved_all_discussions_email.text.erb
@@ -0,0 +1,3 @@
+All discussions on Merge Request <%= @merge_request.to_reference %> were resolved by <%= @resolved_by.name %>
+
+<%= url_for(namespace_project_merge_request_url(@merge_request.target_project.namespace, @merge_request.target_project, @merge_request)) %>
diff --git a/app/views/projects/diffs/_line.html.haml b/app/views/projects/diffs/_line.html.haml
index 891b2bd9802..7042e9f1fc9 100644
--- a/app/views/projects/diffs/_line.html.haml
+++ b/app/views/projects/diffs/_line.html.haml
@@ -1,7 +1,7 @@
 - email = local_assigns.fetch(:email, false)
 - plain = local_assigns.fetch(:plain, false)
 - type = line.type
-- line_code = diff_file.line_code(line) unless plain
+- line_code = diff_file.line_code(line)
 %tr.line_holder{ plain ? { class: type} : { class: type, id: line_code } }
   - case type
   - when 'match'
@@ -28,3 +28,10 @@
         %pre= diff_line_content(line.text, type)
       - else
         = diff_line_content(line.text, type)
+
+- discussions = local_assigns.fetch(:discussions, nil)
+- if discussions && !line.meta?
+  - discussion = discussions[line_code]
+  - if discussion
+    - discussion_expanded = local_assigns.fetch(:discussion_expanded, discussion.expanded?)
+    = render "discussions/diff_discussion", discussion: discussion, expanded: discussion_expanded
diff --git a/app/views/projects/diffs/_text_file.html.haml b/app/views/projects/diffs/_text_file.html.haml
index ab5463ba89d..f1d2d4bf268 100644
--- a/app/views/projects/diffs/_text_file.html.haml
+++ b/app/views/projects/diffs/_text_file.html.haml
@@ -5,15 +5,12 @@
 
 %table.text-file.code.js-syntax-highlight{ data: diff_view_data, class: too_big ? 'hide' : '' }
   - last_line = 0
-  - diff_file.highlighted_diff_lines.each do |line|
-    - last_line = line.new_pos
-    = render "projects/diffs/line", line: line, diff_file: diff_file
-
-    - unless @diff_notes_disabled
-      - line_code = diff_file.line_code(line)
-      - discussion = @grouped_diff_discussions[line_code] if line_code
-      - if discussion
-        = render "discussions/diff_discussion", discussion: discussion
+  - discussions = @grouped_diff_discussions unless @diff_notes_disabled
+  = render partial: "projects/diffs/line",
+    collection: diff_file.highlighted_diff_lines,
+    as: :line,
+    locals: { diff_file: diff_file, discussions: discussions }
 
+  - last_line = diff_file.highlighted_diff_lines.last.new_pos
   - if !diff_file.new_file && last_line > 0
     = diff_match_line last_line, last_line, bottom: true
diff --git a/app/views/projects/merge_requests/_discussion.html.haml b/app/views/projects/merge_requests/_discussion.html.haml
index 53dd300c35c..d070979bcfe 100644
--- a/app/views/projects/merge_requests/_discussion.html.haml
+++ b/app/views/projects/merge_requests/_discussion.html.haml
@@ -4,5 +4,8 @@
       = link_to 'Close merge request', merge_request_path(@merge_request, merge_request: {state_event: :close }), method: :put, class: "btn btn-nr btn-comment btn-close close-mr-link js-note-target-close", title: "Close merge request", data: {original_text: "Close merge request", alternative_text: "Comment & close merge request"}
     - if @merge_request.closed?
       = link_to 'Reopen merge request', merge_request_path(@merge_request, merge_request: {state_event: :reopen }), method: :put, class: "btn btn-nr btn-comment btn-reopen reopen-mr-link js-note-target-reopen", title: "Reopen merge request", data: {original_text: "Reopen merge request", alternative_text: "Comment & reopen merge request"}
+  %comment-and-resolve-btn{ "inline-template" => true, ":discussion-id" => "" }
+    %button.btn.btn-nr.btn-default.append-right-10.js-comment-resolve-button{ "v-if" => "showButton", type: "submit", data: { namespace_path: "#{@merge_request.project.namespace.path}", project_path: "#{@merge_request.project.path}" } }
+      {{ buttonText }}
 
 #notes= render "projects/notes/notes_with_form"
diff --git a/app/views/projects/merge_requests/_show.html.haml b/app/views/projects/merge_requests/_show.html.haml
index a1313064725..f8025fc1dbe 100644
--- a/app/views/projects/merge_requests/_show.html.haml
+++ b/app/views/projects/merge_requests/_show.html.haml
@@ -1,6 +1,8 @@
 - page_title           "#{@merge_request.title} (#{@merge_request.to_reference})", "Merge Requests"
 - page_description     @merge_request.description
 - page_card_attributes @merge_request.card_attributes
+- content_for :page_specific_javascripts do
+  = page_specific_javascript_tag('diff_notes/diff_notes_bundle.js')
 
 - if diff_view == :parallel
   - fluid_layout true
@@ -65,8 +67,18 @@
           = link_to diffs_namespace_project_merge_request_path(@project.namespace, @project, @merge_request), data: { target: 'div#diffs', action: 'diffs', toggle: 'tab' } do
             Changes
             %span.badge= @merge_request.diff_size
+        %li#resolve-count-app.line-resolve-all-container.pull-right.prepend-top-10.hidden-xs{ "v-cloak" => true }
+          %resolve-count{ "inline-template" => true, ":logged-out" => "#{current_user.nil?}"  }
+            .line-resolve-all{ "v-show" => "discussionCount > 0",
+              ":class" => "{ 'has-next-btn': !loggedOut && resolvedDiscussionCount !== discussionCount }" }
+              %span.line-resolve-btn.is-disabled{ type: "button",
+                  ":class" => "{ 'is-active': resolvedDiscussionCount === discussionCount }" }
+                = render "shared/icons/icon_status_success.svg"
+              %span.line-resolve-text
+                {{ resolvedDiscussionCount }}/{{ discussionCount }} {{ discussionCount | pluralize 'discussion' }} resolved
+            = render "discussions/jump_to_next"
 
-      .tab-content
+      .tab-content#diff-notes-app
         #notes.notes.tab-pane.voting_notes
           .content-block.content-block-small.oneline-block
             = render 'award_emoji/awards_block', awardable: @merge_request, inline: true
diff --git a/app/views/projects/notes/_form.html.haml b/app/views/projects/notes/_form.html.haml
index 759c72b2477..402f5b52f5e 100644
--- a/app/views/projects/notes/_form.html.haml
+++ b/app/views/projects/notes/_form.html.haml
@@ -1,4 +1,4 @@
-= form_for [@project.namespace.becomes(Namespace), @project, @note], remote: true, html: { :'data-type' => 'json', multipart: true, id: nil, class: "new-note js-new-note-form js-quick-submit common-note-form" }, authenticity_token: true do |f|
+= form_for [@project.namespace.becomes(Namespace), @project, @note], remote: true, html: { :'data-type' => 'json', multipart: true, id: nil, class: "new-note js-new-note-form js-quick-submit common-note-form", "data-noteable-iid" => @note.noteable.try(:iid), }, authenticity_token: true do |f|
   = hidden_field_tag :view, diff_view
   = hidden_field_tag :line_type
   = note_target_fields(@note)
diff --git a/app/views/projects/notes/_note.html.haml b/app/views/projects/notes/_note.html.haml
index 71da8ac9d7c..d2ac1ce2b9a 100644
--- a/app/views/projects/notes/_note.html.haml
+++ b/app/views/projects/notes/_note.html.haml
@@ -1,5 +1,6 @@
 - return unless note.author
 - return if note.cross_reference_not_visible_for?(current_user)
+- can_resolve = can?(current_user, :resolve_note, note)
 
 - note_editable = note_editable?(note)
 %li.timeline-entry{ id: dom_id(note), class: ["note", "note-row-#{note.id}", ('system-note' if note.system)], data: {author_id: note.author.id, editable: note_editable} }
@@ -16,19 +17,48 @@
             commented
           %a{ href: "##{dom_id(note)}" }
             = time_ago_with_tooltip(note.created_at, placement: 'bottom', html_class: 'note-created-ago')
-        .note-actions
-          - access = note_max_access_for_user(note)
-          - if access and not note.system
-            %span.note-role.hidden-xs= access
-          - if current_user and not note.system
-            = link_to '#', title: 'Award Emoji', class: 'note-action-button note-emoji-button js-add-award js-note-emoji', data: { position: 'right' } do
-              = icon('spinner spin')
-              = icon('smile-o')
-          - if note_editable
-            = link_to '#', title: 'Edit comment', class: 'note-action-button js-note-edit' do
-              = icon('pencil')
-            = link_to namespace_project_note_path(note.project.namespace, note.project, note), title: 'Remove comment', method: :delete, data: { confirm: 'Are you sure you want to remove this comment?' }, remote: true, class: 'note-action-button hidden-xs js-note-delete danger' do
-              = icon('trash-o')
+        - unless note.system?
+          .note-actions
+            - access = note_max_access_for_user(note)
+            - if access
+              %span.note-role.hidden-xs= access
+
+            - if note.resolvable?
+              %resolve-btn{ ":namespace-path" => "'#{note.project.namespace.path}'",
+                  ":project-path" => "'#{note.project.path}'",
+                  ":discussion-id" => "'#{note.discussion_id}'",
+                  ":note-id" => note.id,
+                  ":resolved" => note.resolved?,
+                  ":can-resolve" => can_resolve,
+                  ":resolved-by" => "'#{note.resolved_by.try(:name)}'",
+                  "v-show" => "#{can_resolve || note.resolved?}",
+                  "inline-template" => true,
+                  "v-ref:note_#{note.id}" => true }
+
+                .note-action-button
+                  = icon("spin spinner", "v-show" => "loading")
+                  %button.line-resolve-btn{ type: "button",
+                      class: ("is-disabled" unless can_resolve),
+                      ":class" => "{ 'is-active': isResolved }",
+                      ":aria-label" => "buttonText",
+                      "@click" => "resolve",
+                      ":title" => "buttonText",
+                      "v-show" => "!loading",
+                      "v-el:button" => true }
+
+                    = render "shared/icons/icon_status_success.svg"
+
+            - if current_user
+              - if note.emoji_awardable?
+                = link_to '#', title: 'Award Emoji', class: 'note-action-button note-emoji-button js-add-award js-note-emoji', data: { position: 'right' } do
+                  = icon('spinner spin')
+                  = icon('smile-o')
+
+              - if note_editable
+                = link_to '#', title: 'Edit comment', class: 'note-action-button js-note-edit' do
+                  = icon('pencil')
+                = link_to namespace_project_note_path(note.project.namespace, note.project, note), title: 'Remove comment', method: :delete, data: { confirm: 'Are you sure you want to remove this comment?' }, remote: true, class: 'note-action-button hidden-xs js-note-delete danger' do
+                  = icon('trash-o')
       .note-body{class: note_editable ? 'js-task-list-container' : ''}
         .note-text.md
           = preserve do
diff --git a/app/views/shared/icons/_next_discussion.svg b/app/views/shared/icons/_next_discussion.svg
new file mode 100644
index 00000000000..43559a60cb0
--- /dev/null
+++ b/app/views/shared/icons/_next_discussion.svg
@@ -0,0 +1 @@
+<svg viewBox="0 0 20 19" ><path d="M15.21 7.783h-3.317c-.268 0-.472.218-.472.486v.953c0 .28.212.486.473.486h3.318v1.575c0 .36.233.452.52.23l3.06-2.37c.274-.213.286-.582 0-.804l-3.06-2.37c-.275-.213-.52-.12-.52.23v1.583zm.57-3.66c-1.558-1.22-3.783-1.98-6.254-1.98C4.816 2.143 1 4.91 1 8.333c0 1.964 1.256 3.715 3.216 4.846-.447 1.615-1.132 2.195-1.732 2.882-.142.174-.304.32-.256.56v.01c.047.213.218.368.41.368h.046c.37-.048.743-.116 1.085-.213 1.645-.425 3.13-1.22 4.377-2.34.447.048.913.077 1.38.077 2.092 0 4.01-.546 5.492-1.454-.416-.208-.798-.475-1.134-.792-1.227.63-2.743 1.008-4.36 1.008-.41 0-.828-.03-1.237-.078l-.543-.058-.41.368c-.78.696-1.655 1.248-2.616 1.654.248-.445.486-.977.667-1.664l.257-.928-.828-.484c-1.646-.948-2.598-2.32-2.598-3.763 0-2.69 3.35-4.952 7.308-4.952 1.893 0 3.647.518 4.962 1.353.393-.266.827-.473 1.29-.61z" /></svg>
diff --git a/config/application.rb b/config/application.rb
index 0c136623477..6b80f8ddafa 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -85,6 +85,7 @@ module Gitlab
     config.assets.precompile << "users/users_bundle.js"
     config.assets.precompile << "network/network_bundle.js"
     config.assets.precompile << "profile/profile_bundle.js"
+    config.assets.precompile << "diff_notes/diff_notes_bundle.js"
     config.assets.precompile << "boards/boards_bundle.js"
     config.assets.precompile << "boards/test_utils/simulate_drag.js"
     config.assets.precompile << "lib/utils/*.js"
diff --git a/config/routes.rb b/config/routes.rb
index 5c48bf233d6..66f77aee06a 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -749,6 +749,13 @@ Rails.application.routes.draw do
             get :update_branches
             get :diff_for_path
           end
+
+          resources :discussions, only: [], constraints: { id: /\h{40}/ } do
+            member do
+              post :resolve
+              delete :resolve, action: :unresolve
+            end
+          end
         end
 
         resources :branches, only: [:index, :new, :create, :destroy], constraints: { id: Gitlab::Regex.git_reference_regex }
@@ -858,6 +865,8 @@ Rails.application.routes.draw do
           member do
             post :toggle_award_emoji
             delete :delete_attachment
+            post :resolve
+            delete :resolve, action: :unresolve
           end
         end
 
diff --git a/db/migrate/20160724205507_add_resolved_to_notes.rb b/db/migrate/20160724205507_add_resolved_to_notes.rb
new file mode 100644
index 00000000000..b8ebcdbd156
--- /dev/null
+++ b/db/migrate/20160724205507_add_resolved_to_notes.rb
@@ -0,0 +1,10 @@
+class AddResolvedToNotes < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    add_column :notes, :resolved_at, :datetime
+    add_column :notes, :resolved_by_id, :integer
+  end
+end
diff --git a/db/migrate/20160817154936_add_discussion_ids_to_notes.rb b/db/migrate/20160817154936_add_discussion_ids_to_notes.rb
new file mode 100644
index 00000000000..61facce665a
--- /dev/null
+++ b/db/migrate/20160817154936_add_discussion_ids_to_notes.rb
@@ -0,0 +1,13 @@
+# See http://doc.gitlab.com/ce/development/migration_style_guide.html
+# for more information on how to write migrations for GitLab.
+
+class AddDiscussionIdsToNotes < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+
+  def change
+    add_column :notes, :discussion_id, :string
+    add_column :notes, :original_discussion_id, :string
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index fa56db332b3..82d4590f6b5 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -11,7 +11,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20160816161312) do
+ActiveRecord::Schema.define(version: 20160817154936) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -684,12 +684,16 @@ ActiveRecord::Schema.define(version: 20160816161312) do
     t.string   "line_code"
     t.string   "commit_id"
     t.integer  "noteable_id"
-    t.boolean  "system",            default: false, null: false
+    t.boolean  "system",                 default: false, null: false
     t.text     "st_diff"
     t.integer  "updated_by_id"
     t.string   "type"
     t.text     "position"
     t.text     "original_position"
+    t.datetime "resolved_at"
+    t.integer  "resolved_by_id"
+    t.string   "discussion_id"
+    t.string   "original_discussion_id"
   end
 
   add_index "notes", ["author_id"], name: "index_notes_on_author_id", using: :btree
diff --git a/doc/user/project/merge_requests/img/discussion_view.png b/doc/user/project/merge_requests/img/discussion_view.png
new file mode 100644
index 00000000000..83bb60acce2
--- /dev/null
+++ b/doc/user/project/merge_requests/img/discussion_view.png
diff --git a/doc/user/project/merge_requests/img/discussions_resolved.png b/doc/user/project/merge_requests/img/discussions_resolved.png
new file mode 100644
index 00000000000..85428129ac8
--- /dev/null
+++ b/doc/user/project/merge_requests/img/discussions_resolved.png
diff --git a/doc/user/project/merge_requests/img/resolve_comment_button.png b/doc/user/project/merge_requests/img/resolve_comment_button.png
new file mode 100644
index 00000000000..2c4ab2f5d53
--- /dev/null
+++ b/doc/user/project/merge_requests/img/resolve_comment_button.png
diff --git a/doc/user/project/merge_requests/img/resolve_discussion_button.png b/doc/user/project/merge_requests/img/resolve_discussion_button.png
new file mode 100644
index 00000000000..73f265bb101
--- /dev/null
+++ b/doc/user/project/merge_requests/img/resolve_discussion_button.png
diff --git a/doc/user/project/merge_requests/merge_request_discussion_resolution.md b/doc/user/project/merge_requests/merge_request_discussion_resolution.md
new file mode 100644
index 00000000000..2559f5f5250
--- /dev/null
+++ b/doc/user/project/merge_requests/merge_request_discussion_resolution.md
@@ -0,0 +1,40 @@
+# Merge Request discussion resolution
+
+> [Introduced][ce-5022] in GitLab 8.11.
+
+Discussion resolution helps keep track of progress during code review.
+Resolving comments prevents you from forgetting to address feedback and lets you
+hide discussions that are no longer relevant.
+
+!["A discussion between two people on a piece of code"][discussion-view]
+
+Comments and discussions can be resolved by anyone with at least Developer
+access to the project, as well as by the author of the merge request.
+
+## Marking a comment or discussion as resolved
+
+You can mark a discussion as resolved by clicking the "Resolve discussion"
+button at the bottom of the discussion.
+
+!["Resolve discussion" button][resolve-discussion-button]
+
+Alternatively, you can mark each comment as resolved individually.
+
+!["Resolve comment" button][resolve-comment-button]
+
+## Jumping between unresolved discussions
+
+When a merge request has a large number of comments it can be difficult to track
+what remains unresolved. You can jump between unresolved discussions with the
+Jump button next to the Reply field on a discussion.
+
+You can also jump to the first unresolved discussion from the button next to the
+resolved discussions tracker.
+
+!["3/4 discussions resolved"][discussions-resolved]
+
+[ce-5022]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/5022
+[resolve-discussion-button]: img/resolve_discussion_button.png
+[resolve-comment-button]: img/resolve_comment_button.png
+[discussion-view]: img/discussion_view.png
+[discussions-resolved]: img/discussions_resolved.png
diff --git a/spec/controllers/projects/discussions_controller_spec.rb b/spec/controllers/projects/discussions_controller_spec.rb
new file mode 100644
index 00000000000..ff617fea847
--- /dev/null
+++ b/spec/controllers/projects/discussions_controller_spec.rb
@@ -0,0 +1,125 @@
+require 'spec_helper'
+
+describe Projects::DiscussionsController do
+  let(:user)    { create(:user) }
+  let(:project) { create(:project) }
+  let(:merge_request) { create(:merge_request, source_project: project) }
+  let(:note) { create(:diff_note_on_merge_request, noteable: merge_request, project: project) }
+  let(:discussion) { note.discussion }
+
+  let(:request_params) do
+    {
+      namespace_id: project.namespace,
+      project_id: project,
+      merge_request_id: merge_request,
+      id: note.discussion_id
+    }
+  end
+
+  describe 'POST resolve' do
+    before do
+      sign_in user
+    end
+
+    context "when the user is not authorized to resolve the discussion" do
+      it "returns status 404" do
+        post :resolve, request_params
+
+        expect(response).to have_http_status(404)
+      end
+    end
+
+    context "when the user is authorized to resolve the discussion" do
+      before do
+        project.team << [user, :developer]
+      end
+
+      context "when the discussion is not resolvable" do
+        before do
+          note.update(system: true)
+        end
+
+        it "returns status 404" do
+          post :resolve, request_params
+
+          expect(response).to have_http_status(404)
+        end
+      end
+
+      context "when the discussion is resolvable" do
+        it "resolves the discussion" do
+          post :resolve, request_params
+
+          expect(note.reload.discussion.resolved?).to be true
+          expect(note.reload.discussion.resolved_by).to eq(user)
+        end
+
+        it "sends notifications if all discussions are resolved" do
+          expect_any_instance_of(MergeRequests::ResolvedDiscussionNotificationService).to receive(:execute).with(merge_request)
+
+          post :resolve, request_params
+        end
+
+        it "returns the name of the resolving user" do
+          post :resolve, request_params
+
+          expect(JSON.parse(response.body)["resolved_by"]).to eq(user.name)
+        end
+
+        it "returns status 200" do
+          post :resolve, request_params
+
+          expect(response).to have_http_status(200)
+        end
+      end
+    end
+  end
+
+  describe 'DELETE unresolve' do
+    before do
+      sign_in user
+
+      note.discussion.resolve!(user)
+    end
+
+    context "when the user is not authorized to resolve the discussion" do
+      it "returns status 404" do
+        delete :unresolve, request_params
+
+        expect(response).to have_http_status(404)
+      end
+    end
+
+    context "when the user is authorized to resolve the discussion" do
+      before do
+        project.team << [user, :developer]
+      end
+
+      context "when the discussion is not resolvable" do
+        before do
+          note.update(system: true)
+        end
+
+        it "returns status 404" do
+          delete :unresolve, request_params
+
+          expect(response).to have_http_status(404)
+        end
+      end
+
+      context "when the discussion is resolvable" do
+        it "unresolves the discussion" do
+          delete :unresolve, request_params
+
+          expect(note.reload.discussion.resolved?).to be false
+        end
+
+        it "returns status 200" do
+          delete :unresolve, request_params
+
+          expect(response).to have_http_status(200)
+        end
+      end
+    end
+  end
+end
diff --git a/spec/controllers/projects/notes_controller_spec.rb b/spec/controllers/projects/notes_controller_spec.rb
index 75590c1ed4f..92e38b02615 100644
--- a/spec/controllers/projects/notes_controller_spec.rb
+++ b/spec/controllers/projects/notes_controller_spec.rb
@@ -1,4 +1,4 @@
-require('spec_helper')
+require 'spec_helper'
 
 describe Projects::NotesController do
   let(:user)    { create(:user) }
@@ -6,7 +6,15 @@ describe Projects::NotesController do
   let(:issue)   { create(:issue, project: project) }
   let(:note)    { create(:note, noteable: issue, project: project) }
 
-  describe 'POST #toggle_award_emoji' do
+  let(:request_params) do
+    {
+      namespace_id: project.namespace,
+      project_id: project,
+      id: note
+    }
+  end
+
+  describe 'POST toggle_award_emoji' do
     before do
       sign_in(user)
       project.team << [user, :developer]
@@ -14,23 +22,132 @@ describe Projects::NotesController do
 
     it "toggles the award emoji" do
       expect do
-        post(:toggle_award_emoji, namespace_id: project.namespace.path,
-                                  project_id: project.path, id: note.id, name: "thumbsup")
+        post(:toggle_award_emoji, request_params.merge(name: "thumbsup"))
       end.to change { note.award_emoji.count }.by(1)
 
       expect(response).to have_http_status(200)
     end
 
     it "removes the already awarded emoji" do
-      post(:toggle_award_emoji, namespace_id: project.namespace.path,
-                                project_id: project.path, id: note.id, name: "thumbsup")
+      post(:toggle_award_emoji, request_params.merge(name: "thumbsup"))
 
       expect do
-        post(:toggle_award_emoji, namespace_id: project.namespace.path,
-                                  project_id: project.path, id: note.id, name: "thumbsup")
+        post(:toggle_award_emoji, request_params.merge(name: "thumbsup"))
       end.to change { AwardEmoji.count }.by(-1)
 
       expect(response).to have_http_status(200)
     end
   end
+
+  describe "resolving and unresolving" do
+    let(:merge_request) { create(:merge_request, source_project: project) }
+    let(:note) { create(:diff_note_on_merge_request, noteable: merge_request, project: project) }
+
+    describe 'POST resolve' do
+      before do
+        sign_in user
+      end
+
+      context "when the user is not authorized to resolve the note" do
+        it "returns status 404" do
+          post :resolve, request_params
+
+          expect(response).to have_http_status(404)
+        end
+      end
+
+      context "when the user is authorized to resolve the note" do
+        before do
+          project.team << [user, :developer]
+        end
+
+        context "when the note is not resolvable" do
+          before do
+            note.update(system: true)
+          end
+
+          it "returns status 404" do
+            post :resolve, request_params
+
+            expect(response).to have_http_status(404)
+          end
+        end
+
+        context "when the note is resolvable" do
+          it "resolves the note" do
+            post :resolve, request_params
+
+            expect(note.reload.resolved?).to be true
+            expect(note.reload.resolved_by).to eq(user)
+          end
+
+          it "sends notifications if all discussions are resolved" do
+            expect_any_instance_of(MergeRequests::ResolvedDiscussionNotificationService).to receive(:execute).with(merge_request)
+
+            post :resolve, request_params
+          end
+
+          it "returns the name of the resolving user" do
+            post :resolve, request_params
+
+            expect(JSON.parse(response.body)["resolved_by"]).to eq(user.name)
+          end
+
+          it "returns status 200" do
+            post :resolve, request_params
+
+            expect(response).to have_http_status(200)
+          end
+        end
+      end
+    end
+
+    describe 'DELETE unresolve' do
+      before do
+        sign_in user
+
+        note.resolve!(user)
+      end
+
+      context "when the user is not authorized to resolve the note" do
+        it "returns status 404" do
+          delete :unresolve, request_params
+
+          expect(response).to have_http_status(404)
+        end
+      end
+
+      context "when the user is authorized to resolve the note" do
+        before do
+          project.team << [user, :developer]
+        end
+
+        context "when the note is not resolvable" do
+          before do
+            note.update(system: true)
+          end
+
+          it "returns status 404" do
+            delete :unresolve, request_params
+
+            expect(response).to have_http_status(404)
+          end
+        end
+
+        context "when the note is resolvable" do
+          it "unresolves the note" do
+            delete :unresolve, request_params
+
+            expect(note.reload.resolved?).to be false
+          end
+
+          it "returns status 200" do
+            delete :unresolve, request_params
+
+            expect(response).to have_http_status(200)
+          end
+        end
+      end
+    end
+  end
 end
diff --git a/spec/features/merge_requests/diff_notes_resolve_spec.rb b/spec/features/merge_requests/diff_notes_resolve_spec.rb
new file mode 100644
index 00000000000..c6adf7e4c56
--- /dev/null
+++ b/spec/features/merge_requests/diff_notes_resolve_spec.rb
@@ -0,0 +1,497 @@
+require 'spec_helper'
+
+feature 'Diff notes resolve', feature: true, js: true do
+  let(:user)          { create(:user) }
+  let(:project)       { create(:project, :public) }
+  let(:merge_request) { create(:merge_request_with_diffs, source_project: project, author: user, title: "Bug NS-04") }
+  let!(:note)         { create(:diff_note_on_merge_request, project: project, noteable: merge_request) }
+  let(:path)          { "files/ruby/popen.rb" }
+  let(:position) do
+    Gitlab::Diff::Position.new(
+      old_path: path,
+      new_path: path,
+      old_line: nil,
+      new_line: 9,
+      diff_refs: merge_request.diff_refs
+    )
+  end
+
+  context 'no discussions' do
+    before do
+      project.team << [user, :master]
+      login_as user
+      note.destroy
+      visit_merge_request
+    end
+
+    it 'displays no discussion resolved data' do
+      expect(page).not_to have_content('discussion resolved')
+      expect(page).not_to have_selector('.discussion-next-btn')
+    end
+  end
+
+  context 'as authorized user' do
+    before do
+      project.team << [user, :master]
+      login_as user
+      visit_merge_request
+    end
+
+    context 'single discussion' do
+      it 'shows text with how many discussions' do
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+
+      it 'allows user to mark a note as resolved' do
+        page.within '.diff-content .note' do
+          find('.line-resolve-btn').click
+
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+          expect(find('.line-resolve-btn')['data-original-title']).to eq("Resolved by #{user.name}")
+        end
+
+        page.within '.diff-content' do
+          expect(page).to have_selector('.btn', text: 'Unresolve discussion')
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to mark discussion as resolved' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+        end
+
+        page.within '.diff-content .note' do
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+
+          expect(find('.line-resolve-btn')['data-original-title']).to eq("Resolved by #{user.name}")
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to unresolve discussion' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+          click_button 'Unresolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+
+      it 'hides resolved discussion' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+        end
+
+        visit_merge_request
+
+        expect(page).to have_selector('.discussion-body', visible: false)
+      end
+
+      it 'allows user to resolve from reply form without a comment' do
+        page.within '.diff-content' do
+          click_button 'Reply...'
+
+          click_button 'Resolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to unresolve from reply form without a comment' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+          sleep 1
+
+          click_button 'Reply...'
+
+          click_button 'Unresolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+          expect(page).not_to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to comment & resolve discussion' do
+        page.within '.diff-content' do
+          click_button 'Reply...'
+
+          find('.js-note-text').set 'testing'
+
+          click_button 'Comment & resolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to comment & unresolve discussion' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+
+          click_button 'Reply...'
+
+          find('.js-note-text').set 'testing'
+
+          click_button 'Comment & unresolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+
+      it 'allows user to quickly scroll to next unresolved discussion' do
+        page.within '.line-resolve-all-container' do
+          page.find('.discussion-next-btn').click
+        end
+
+        expect(page.evaluate_script("$('body').scrollTop()")).to be > 0
+      end
+
+      it 'hides jump to next button when all resolved' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+        end
+
+        expect(page).to have_selector('.discussion-next-btn', visible: false)
+      end
+
+      it 'updates updated text after resolving note' do
+        page.within '.diff-content .note' do
+          find('.line-resolve-btn').click
+        end
+
+        expect(page).to have_content("Resolved by #{user.name}")
+      end
+
+      it 'hides jump to next discussion button' do
+        page.within '.discussion-reply-holder' do
+          expect(page).not_to have_selector('.discussion-next-btn')
+        end
+      end
+    end
+
+    context 'multiple notes' do
+      before do
+        create(:diff_note_on_merge_request, project: project, noteable: merge_request)
+      end
+
+      it 'does not mark discussion as resolved when resolving single note' do
+        page.within '.diff-content .note' do
+          first('.line-resolve-btn').click
+          sleep 1
+          expect(first('.line-resolve-btn')['data-original-title']).to eq("Resolved by #{user.name}")
+        end
+
+        expect(page).to have_content('Last updated')
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+
+      it 'resolves discussion' do
+        page.all('.note').each do |note|
+          note.find('.line-resolve-btn').click
+        end
+
+        expect(page).to have_content('Resolved by')
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+        end
+      end
+    end
+
+    context 'muliple discussions' do
+      before do
+        create(:diff_note_on_merge_request, project: project, position: position, noteable: merge_request)
+        visit_merge_request
+      end
+
+      it 'shows text with how many discussions' do
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/2 discussions resolved')
+        end
+      end
+
+      it 'allows user to mark a single note as resolved' do
+        click_button('Resolve discussion', match: :first)
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/2 discussions resolved')
+        end
+      end
+
+      it 'allows user to mark all notes as resolved' do
+        page.all('.line-resolve-btn').each do |btn|
+          btn.click
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('2/2 discussions resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user user to mark all discussions as resolved' do
+        page.all('.discussion-reply-holder').each do |reply_holder|
+          page.within reply_holder do
+            click_button 'Resolve discussion'
+          end
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('2/2 discussions resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to quickly scroll to next unresolved discussion' do
+        page.within first('.discussion-reply-holder') do
+          click_button 'Resolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          page.find('.discussion-next-btn').click
+        end
+
+        expect(page.evaluate_script("$('body').scrollTop()")).to be > 0
+      end
+
+      it 'updates updated text after resolving note' do
+        page.within first('.diff-content .note') do
+          find('.line-resolve-btn').click
+        end
+
+        expect(page).to have_content("Resolved by #{user.name}")
+      end
+
+      it 'shows jump to next discussion button' do
+        page.all('.discussion-reply-holder').each do |holder|
+          expect(holder).to have_selector('.discussion-next-btn')
+        end
+      end
+      
+      it 'displays next discussion even if hidden' do
+        page.all('.note-discussion').each do |discussion|
+          page.within discussion do
+            click_link 'Toggle discussion'
+          end
+        end
+
+        page.within('.issuable-discussion #notes') do
+          expect(page).not_to have_selector('.btn', text: 'Resolve discussion')
+        end
+
+        page.within '.line-resolve-all-container' do
+          page.find('.discussion-next-btn').click
+        end
+
+        expect(find('.discussion-with-resolve-btn')).to have_selector('.btn', text: 'Resolve discussion')
+      end
+    end
+
+    context 'changes tab' do
+      it 'shows text with how many discussions' do
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+
+      it 'allows user to mark a note as resolved' do
+        page.within '.diff-content .note' do
+          find('.line-resolve-btn').click
+
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+
+        page.within '.diff-content' do
+          expect(page).to have_selector('.btn', text: 'Unresolve discussion')
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to mark discussion as resolved' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+        end
+
+        page.within '.diff-content .note' do
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to unresolve discussion' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+          click_button 'Unresolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+
+      it 'allows user to comment & resolve discussion' do
+        page.within '.diff-content' do
+          click_button 'Reply...'
+
+          find('.js-note-text').set 'testing'
+
+          click_button 'Comment & resolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+
+      it 'allows user to comment & unresolve discussion' do
+        page.within '.diff-content' do
+          click_button 'Resolve discussion'
+
+          click_button 'Reply...'
+
+          find('.js-note-text').set 'testing'
+
+          click_button 'Comment & unresolve discussion'
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+    end
+  end
+
+  context 'as a guest' do
+    let(:guest) { create(:user) }
+
+    before do
+      project.team << [guest, :guest]
+      login_as guest
+    end
+
+    context 'someone elses merge request' do
+      before do
+        visit_merge_request
+      end
+
+      it 'does not allow user to mark note as resolved' do
+        page.within '.diff-content .note' do
+          expect(page).not_to have_selector('.line-resolve-btn')
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+
+      it 'does not allow user to mark discussion as resolved' do
+        page.within '.diff-content .note' do
+          expect(page).not_to have_selector('.btn', text: 'Resolve discussion')
+        end
+      end
+    end
+
+    context 'guest users merge request' do
+      before do
+        mr = create(:merge_request_with_diffs, source_project: project, source_branch: 'markdown', author: guest, title: "Bug")
+        create(:diff_note_on_merge_request, project: project, noteable: mr)
+        visit_merge_request(mr)
+      end
+
+      it 'allows user to mark a note as resolved' do
+        page.within '.diff-content .note' do
+          find('.line-resolve-btn').click
+
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+
+        page.within '.diff-content' do
+          expect(page).to have_selector('.btn', text: 'Unresolve discussion')
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('1/1 discussion resolved')
+          expect(page).to have_selector('.line-resolve-btn.is-active')
+        end
+      end
+    end
+  end
+
+  context 'unauthorized user' do
+    context 'no resolved comments' do
+      before do
+        visit_merge_request
+      end
+
+      it 'does not allow user to mark note as resolved' do
+        page.within '.diff-content .note' do
+          expect(page).not_to have_selector('.line-resolve-btn')
+        end
+
+        page.within '.line-resolve-all-container' do
+          expect(page).to have_content('0/1 discussion resolved')
+        end
+      end
+    end
+
+    context 'resolved comment' do
+      before do
+        note.resolve!(user)
+        visit_merge_request
+      end
+
+      it 'shows resolved icon' do
+        expect(page).to have_content '1/1 discussion resolved'
+
+        click_link 'Toggle discussion'
+        expect(page).to have_selector('.line-resolve-btn.is-active')
+      end
+
+      it 'does not allow user to click resolve button' do
+        expect(page).to have_selector('.line-resolve-btn.is-disabled')
+        click_link 'Toggle discussion'
+
+        expect(page).to have_selector('.line-resolve-btn.is-disabled')
+      end
+    end
+  end
+
+  def visit_merge_request(mr = nil)
+    mr = mr || merge_request
+    visit namespace_project_merge_request_path(mr.project.namespace, mr.project, mr)
+  end
+end
diff --git a/spec/javascripts/diff_comments_store_spec.js.es6 b/spec/javascripts/diff_comments_store_spec.js.es6
new file mode 100644
index 00000000000..22293d4de87
--- /dev/null
+++ b/spec/javascripts/diff_comments_store_spec.js.es6
@@ -0,0 +1,122 @@
+//= require vue
+//= require diff_notes/models/discussion
+//= require diff_notes/models/note
+//= require diff_notes/stores/comments
+(() => {
+  function createDiscussion(noteId = 1, resolved = true) {
+    CommentsStore.create('a', noteId, true, resolved, 'test');
+  };
+
+  beforeEach(() => {
+    CommentsStore.state = {};
+  });
+
+  describe('New discussion', () => {
+    it('creates new discussion', () => {
+      expect(Object.keys(CommentsStore.state).length).toBe(0);
+      createDiscussion();
+      expect(Object.keys(CommentsStore.state).length).toBe(1);
+    });
+
+    it('creates new note in discussion', () => {
+      createDiscussion();
+      createDiscussion(2);
+
+      const discussion = CommentsStore.state['a'];
+      expect(Object.keys(discussion.notes).length).toBe(2);
+    });
+  });
+
+  describe('Get note', () => {
+    beforeEach(() => {
+      expect(Object.keys(CommentsStore.state).length).toBe(0);
+      createDiscussion();
+    });
+
+    it('gets note by ID', () => {
+      const note = CommentsStore.get('a', 1);
+      expect(note).toBeDefined();
+      expect(note.id).toBe(1);
+    });
+  });
+
+  describe('Delete discussion', () => {
+    beforeEach(() => {
+      expect(Object.keys(CommentsStore.state).length).toBe(0);
+      createDiscussion();
+    });
+
+    it('deletes discussion by ID', () => {
+      CommentsStore.delete('a', 1);
+      expect(Object.keys(CommentsStore.state).length).toBe(0);
+    });
+
+    it('deletes discussion when no more notes', () => {
+      createDiscussion();
+      createDiscussion(2);
+      expect(Object.keys(CommentsStore.state).length).toBe(1);
+      expect(Object.keys(CommentsStore.state['a'].notes).length).toBe(2);
+
+      CommentsStore.delete('a', 1);
+      CommentsStore.delete('a', 2);
+      expect(Object.keys(CommentsStore.state).length).toBe(0);
+    });
+  });
+
+  describe('Update note', () => {
+    beforeEach(() => {
+      expect(Object.keys(CommentsStore.state).length).toBe(0);
+      createDiscussion();
+    });
+
+    it('updates note to be unresolved', () => {
+      CommentsStore.update('a', 1, false, 'test');
+
+      const note = CommentsStore.get('a', 1);
+      expect(note.resolved).toBe(false);
+    });
+  });
+
+  describe('Discussion resolved', () => {
+    beforeEach(() => {
+      expect(Object.keys(CommentsStore.state).length).toBe(0);
+      createDiscussion();
+    });
+
+    it('is resolved with single note', () => {
+      const discussion = CommentsStore.state['a'];
+      expect(discussion.isResolved()).toBe(true);
+    });
+
+    it('is unresolved with 2 notes', () => {
+      const discussion = CommentsStore.state['a'];
+      createDiscussion(2, false);
+      console.log(discussion.isResolved());
+
+      expect(discussion.isResolved()).toBe(false);
+    });
+
+    it('is resolved with 2 notes', () => {
+      const discussion = CommentsStore.state['a'];
+      createDiscussion(2);
+
+      expect(discussion.isResolved()).toBe(true);
+    });
+
+    it('resolve all notes', () => {
+      const discussion = CommentsStore.state['a'];
+      createDiscussion(2, false);
+
+      discussion.resolveAllNotes();
+      expect(discussion.isResolved()).toBe(true);
+    });
+
+    it('unresolve all notes', () => {
+      const discussion = CommentsStore.state['a'];
+      createDiscussion(2);
+
+      discussion.unResolveAllNotes();
+      expect(discussion.isResolved()).toBe(false);
+    });
+  });
+})();
diff --git a/spec/mailers/emails/merge_requests_spec.rb b/spec/mailers/emails/merge_requests_spec.rb
new file mode 100644
index 00000000000..4d3811af254
--- /dev/null
+++ b/spec/mailers/emails/merge_requests_spec.rb
@@ -0,0 +1,19 @@
+require 'spec_helper'
+require 'email_spec'
+require 'mailers/shared/notify'
+
+describe Notify, "merge request notifications" do
+  include EmailSpec::Matchers
+
+  describe "#resolved_all_discussions_email" do
+    let(:user) { create(:user) }
+    let(:merge_request) { create(:merge_request) }
+    let(:current_user) { create(:user) }
+
+    subject { Notify.resolved_all_discussions_email(user.id, merge_request.id, current_user.id) }
+
+    it "includes the name of the resolver" do
+      expect(subject).to have_body_text current_user.name
+    end
+  end
+end
diff --git a/spec/models/diff_note_spec.rb b/spec/models/diff_note_spec.rb
index 1fa96eb1f15..6a640474cfe 100644
--- a/spec/models/diff_note_spec.rb
+++ b/spec/models/diff_note_spec.rb
@@ -103,7 +103,7 @@ describe DiffNote, models: true do
 
   describe "#active?" do
     context "when noteable is a commit" do
-      subject { create(:diff_note_on_commit, project: project, position: position) }
+      subject { build(:diff_note_on_commit, project: project, position: position) }
 
       it "returns true" do
         expect(subject.active?).to be true
@@ -188,4 +188,300 @@ describe DiffNote, models: true do
       end
     end
   end
+
+  describe "#resolvable?" do
+    context "when noteable is a commit" do
+      subject { create(:diff_note_on_commit, project: project, position: position) }
+
+      it "returns false" do
+        expect(subject.resolvable?).to be false
+      end
+    end
+
+    context "when noteable is a merge request" do
+      context "when a system note" do
+        before do
+          subject.system = true
+        end
+
+        it "returns false" do
+          expect(subject.resolvable?).to be false
+        end
+      end
+
+      context "when a regular note" do
+        it "returns true" do
+          expect(subject.resolvable?).to be true
+        end
+      end
+    end
+  end
+
+  describe "#to_be_resolved?" do
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns false" do
+        expect(subject.to_be_resolved?).to be false
+      end
+    end
+
+    context "when resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when resolved" do
+        before do
+          allow(subject).to receive(:resolved?).and_return(true)
+        end
+
+        it "returns false" do
+          expect(subject.to_be_resolved?).to be false
+        end
+      end
+
+      context "when not resolved" do
+        before do
+          allow(subject).to receive(:resolved?).and_return(false)
+        end
+
+        it "returns true" do
+          expect(subject.to_be_resolved?).to be true
+        end
+      end
+    end
+  end
+
+  describe "#resolve!" do
+    let(:current_user) { create(:user) }
+
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns nil" do
+        expect(subject.resolve!(current_user)).to be_nil
+      end
+
+      it "doesn't set resolved_at" do
+        subject.resolve!(current_user)
+
+        expect(subject.resolved_at).to be_nil
+      end
+
+      it "doesn't set resolved_by" do
+        subject.resolve!(current_user)
+
+        expect(subject.resolved_by).to be_nil
+      end
+
+      it "doesn't mark as resolved" do
+        subject.resolve!(current_user)
+
+        expect(subject.resolved?).to be false
+      end
+    end
+
+    context "when resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when already resolved" do
+        let(:user) { create(:user) }
+
+        before do
+          subject.resolve!(user)
+        end
+
+        it "returns nil" do
+          expect(subject.resolve!(current_user)).to be_nil
+        end
+
+        it "doesn't change resolved_at" do
+          expect(subject.resolved_at).not_to be_nil
+
+          expect { subject.resolve!(current_user) }.not_to change { subject.resolved_at }
+        end
+
+        it "doesn't change resolved_by" do
+          expect(subject.resolved_by).to eq(user)
+
+          expect { subject.resolve!(current_user) }.not_to change { subject.resolved_by }
+        end
+
+        it "doesn't change resolved status" do
+          expect(subject.resolved?).to be true
+
+          expect { subject.resolve!(current_user) }.not_to change { subject.resolved? }
+        end
+      end
+
+      context "when not yet resolved" do
+        it "returns true" do
+          expect(subject.resolve!(current_user)).to be true
+        end
+
+        it "sets resolved_at" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved_at).not_to be_nil
+        end
+
+        it "sets resolved_by" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved_by).to eq(current_user)
+        end
+
+        it "marks as resolved" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved?).to be true
+        end
+      end
+    end
+  end
+
+  describe "#unresolve!" do
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns nil" do
+        expect(subject.unresolve!).to be_nil
+      end
+    end
+
+    context "when resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when resolved" do
+        let(:user) { create(:user) }
+
+        before do
+          subject.resolve!(user)
+        end
+
+        it "returns true" do
+          expect(subject.unresolve!).to be true
+        end
+
+        it "unsets resolved_at" do
+          subject.unresolve!
+
+          expect(subject.resolved_at).to be_nil
+        end
+
+        it "unsets resolved_by" do
+          subject.unresolve!
+
+          expect(subject.resolved_by).to be_nil
+        end
+
+        it "unmarks as resolved" do
+          subject.unresolve!
+
+          expect(subject.resolved?).to be false
+        end
+      end
+
+      context "when not resolved" do
+        it "returns nil" do
+          expect(subject.unresolve!).to be_nil
+        end
+      end
+    end
+  end
+
+  describe "#discussion" do
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns nil" do
+        expect(subject.discussion).to be_nil
+      end
+    end
+
+    context "when resolvable" do
+      let!(:diff_note2) { create(:diff_note_on_merge_request, project: project, noteable: merge_request, position: subject.position) }
+      let!(:diff_note3) { create(:diff_note_on_merge_request, project: project, noteable: merge_request, position: active_position2) }
+
+      let(:active_position2) do
+        Gitlab::Diff::Position.new(
+          old_path: "files/ruby/popen.rb",
+          new_path: "files/ruby/popen.rb",
+          old_line: 16,
+          new_line: 22,
+          diff_refs: merge_request.diff_refs
+        )
+      end
+
+      it "returns the discussion this note is in" do
+        discussion = subject.discussion
+
+        expect(discussion.id).to eq(subject.discussion_id)
+        expect(discussion.notes).to eq([subject, diff_note2])
+      end
+    end
+  end
+
+  describe "#discussion_id" do
+    let(:note) { create(:diff_note_on_merge_request) }
+
+    context "when it is newly created" do
+      it "has a discussion id" do
+        expect(note.discussion_id).not_to be_nil
+        expect(note.discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+
+    context "when it didn't store a discussion id before" do
+      before do
+        note.update_column(:discussion_id, nil)
+      end
+
+      it "has a discussion id" do
+        # The discussion_id is set in `after_initialize`, so `reload` won't work
+        reloaded_note = Note.find(note.id)
+
+        expect(reloaded_note.discussion_id).not_to be_nil
+        expect(reloaded_note.discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+  end
+
+  describe "#original_discussion_id" do
+    let(:note) { create(:diff_note_on_merge_request) }
+
+    context "when it is newly created" do
+      it "has a discussion id" do
+        expect(note.original_discussion_id).not_to be_nil
+        expect(note.original_discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+
+    context "when it didn't store a discussion id before" do
+      before do
+        note.update_column(:original_discussion_id, nil)
+      end
+
+      it "has a discussion id" do
+        # The original_discussion_id is set in `after_initialize`, so `reload` won't work
+        reloaded_note = Note.find(note.id)
+
+        expect(reloaded_note.original_discussion_id).not_to be_nil
+        expect(reloaded_note.original_discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+  end
 end
diff --git a/spec/models/discussion_spec.rb b/spec/models/discussion_spec.rb
new file mode 100644
index 00000000000..179f2e73662
--- /dev/null
+++ b/spec/models/discussion_spec.rb
@@ -0,0 +1,615 @@
+require 'spec_helper'
+
+describe Discussion, model: true do
+  subject { described_class.new([first_note, second_note, third_note]) }
+
+  let(:first_note) { create(:diff_note_on_merge_request) }
+  let(:second_note) { create(:diff_note_on_merge_request) }
+  let(:third_note) { create(:diff_note_on_merge_request) }
+
+  describe "#resolvable?" do
+    context "when a diff discussion" do
+      before do
+        allow(subject).to receive(:diff_discussion?).and_return(true)
+      end
+
+      context "when all notes are unresolvable" do
+        before do
+          allow(first_note).to receive(:resolvable?).and_return(false)
+          allow(second_note).to receive(:resolvable?).and_return(false)
+          allow(third_note).to receive(:resolvable?).and_return(false)
+        end
+
+        it "returns false" do
+          expect(subject.resolvable?).to be false
+        end
+      end
+
+      context "when some notes are unresolvable and some notes are resolvable" do
+        before do
+          allow(first_note).to receive(:resolvable?).and_return(true)
+          allow(second_note).to receive(:resolvable?).and_return(false)
+          allow(third_note).to receive(:resolvable?).and_return(true)
+        end
+
+        it "returns true" do
+          expect(subject.resolvable?).to be true
+        end
+      end
+
+      context "when all notes are resolvable" do
+        before do
+          allow(first_note).to receive(:resolvable?).and_return(true)
+          allow(second_note).to receive(:resolvable?).and_return(true)
+          allow(third_note).to receive(:resolvable?).and_return(true)
+        end
+
+        it "returns true" do
+          expect(subject.resolvable?).to be true
+        end
+      end
+    end
+
+    context "when not a diff discussion" do
+      before do
+        allow(subject).to receive(:diff_discussion?).and_return(false)
+      end
+
+      it "returns false" do
+        expect(subject.resolvable?).to be false
+      end
+    end
+  end
+
+  describe "#resolved?" do
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns false" do
+        expect(subject.resolved?).to be false
+      end
+    end
+
+    context "when resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+
+        allow(first_note).to receive(:resolvable?).and_return(true)
+        allow(second_note).to receive(:resolvable?).and_return(false)
+        allow(third_note).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when all resolvable notes are resolved" do
+        before do
+          allow(first_note).to receive(:resolved?).and_return(true)
+          allow(third_note).to receive(:resolved?).and_return(true)
+        end
+
+        it "returns true" do
+          expect(subject.resolved?).to be true
+        end
+      end
+
+      context "when some resolvable notes are not resolved" do
+        before do
+          allow(first_note).to receive(:resolved?).and_return(true)
+          allow(third_note).to receive(:resolved?).and_return(false)
+        end
+
+        it "returns false" do
+          expect(subject.resolved?).to be false
+        end
+      end
+    end
+  end
+
+  describe "#to_be_resolved?" do
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns false" do
+        expect(subject.to_be_resolved?).to be false
+      end
+    end
+
+    context "when resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+
+        allow(first_note).to receive(:resolvable?).and_return(true)
+        allow(second_note).to receive(:resolvable?).and_return(false)
+        allow(third_note).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when all resolvable notes are resolved" do
+        before do
+          allow(first_note).to receive(:resolved?).and_return(true)
+          allow(third_note).to receive(:resolved?).and_return(true)
+        end
+
+        it "returns false" do
+          expect(subject.to_be_resolved?).to be false
+        end
+      end
+
+      context "when some resolvable notes are not resolved" do
+        before do
+          allow(first_note).to receive(:resolved?).and_return(true)
+          allow(third_note).to receive(:resolved?).and_return(false)
+        end
+
+        it "returns true" do
+          expect(subject.to_be_resolved?).to be true
+        end
+      end
+    end
+  end
+
+  describe "#can_resolve?" do
+    let(:current_user) { create(:user) }
+
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns false" do
+        expect(subject.can_resolve?(current_user)).to be false
+      end
+    end
+
+    context "when resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when not signed in" do
+        let(:current_user) { nil }
+
+        it "returns false" do
+          expect(subject.can_resolve?(current_user)).to be false
+        end
+      end
+
+      context "when signed in" do
+        context "when the signed in user is the noteable author" do
+          before do
+            subject.noteable.author = current_user
+          end
+
+          it "returns true" do
+            expect(subject.can_resolve?(current_user)).to be true
+          end
+        end
+
+        context "when the signed in user can push to the project" do
+          before do
+            subject.project.team << [current_user, :master]
+          end
+
+          it "returns true" do
+            expect(subject.can_resolve?(current_user)).to be true
+          end
+        end
+
+        context "when the signed in user is a random user" do
+          it "returns false" do
+            expect(subject.can_resolve?(current_user)).to be false
+          end
+        end
+      end
+    end
+  end
+
+  describe "#resolve!" do
+    let(:current_user) { create(:user) }
+
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns nil" do
+        expect(subject.resolve!(current_user)).to be_nil
+      end
+
+      it "doesn't set resolved_at" do
+        subject.resolve!(current_user)
+
+        expect(subject.resolved_at).to be_nil
+      end
+
+      it "doesn't set resolved_by" do
+        subject.resolve!(current_user)
+
+        expect(subject.resolved_by).to be_nil
+      end
+
+      it "doesn't mark as resolved" do
+        subject.resolve!(current_user)
+
+        expect(subject.resolved?).to be false
+      end
+    end
+
+    context "when resolvable" do
+      let(:user) { create(:user) }
+
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+
+        allow(first_note).to receive(:resolvable?).and_return(true)
+        allow(second_note).to receive(:resolvable?).and_return(false)
+        allow(third_note).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when all resolvable notes are resolved" do
+        before do
+          first_note.resolve!(user)
+          third_note.resolve!(user)
+        end
+
+        it "calls resolve! on every resolvable note" do
+          expect(first_note).to receive(:resolve!).with(current_user)
+          expect(second_note).not_to receive(:resolve!)
+          expect(third_note).to receive(:resolve!).with(current_user)
+
+          subject.resolve!(current_user)
+        end
+
+        it "doesn't change resolved_at on the resolved notes" do
+          expect(first_note.resolved_at).not_to be_nil
+          expect(third_note.resolved_at).not_to be_nil
+
+          expect { subject.resolve!(current_user) }.not_to change { first_note.resolved_at }
+          expect { subject.resolve!(current_user) }.not_to change { third_note.resolved_at }
+        end
+
+        it "doesn't change resolved_by on the resolved notes" do
+          expect(first_note.resolved_by).to eq(user)
+          expect(third_note.resolved_by).to eq(user)
+
+          expect { subject.resolve!(current_user) }.not_to change { first_note.resolved_by }
+          expect { subject.resolve!(current_user) }.not_to change { third_note.resolved_by }
+        end
+
+        it "doesn't change the resolved state on the resolved notes" do
+          expect(first_note.resolved?).to be true
+          expect(third_note.resolved?).to be true
+
+          expect { subject.resolve!(current_user) }.not_to change { first_note.resolved? }
+          expect { subject.resolve!(current_user) }.not_to change { third_note.resolved? }
+        end
+
+        it "doesn't change resolved_at" do
+          expect(subject.resolved_at).not_to be_nil
+
+          expect { subject.resolve!(current_user) }.not_to change { subject.resolved_at }
+        end
+
+        it "doesn't change resolved_by" do
+          expect(subject.resolved_by).to eq(user)
+
+          expect { subject.resolve!(current_user) }.not_to change { subject.resolved_by }
+        end
+
+        it "doesn't change resolved state" do
+          expect(subject.resolved?).to be true
+
+          expect { subject.resolve!(current_user) }.not_to change { subject.resolved? }
+        end
+      end
+
+      context "when some resolvable notes are resolved" do
+        before do
+          first_note.resolve!(user)
+        end
+
+        it "calls resolve! on every resolvable note" do
+          expect(first_note).to receive(:resolve!).with(current_user)
+          expect(second_note).not_to receive(:resolve!)
+          expect(third_note).to receive(:resolve!).with(current_user)
+
+          subject.resolve!(current_user)
+        end
+
+        it "doesn't change resolved_at on the resolved note" do
+          expect(first_note.resolved_at).not_to be_nil
+
+          expect { subject.resolve!(current_user) }.not_to change { first_note.resolved_at }
+        end
+
+        it "doesn't change resolved_by on the resolved note" do
+          expect(first_note.resolved_by).to eq(user)
+
+          expect { subject.resolve!(current_user) }.not_to change { first_note.resolved_by }
+        end
+
+        it "doesn't change the resolved state on the resolved note" do
+          expect(first_note.resolved?).to be true
+
+          expect { subject.resolve!(current_user) }.not_to change { first_note.resolved? }
+        end
+
+        it "sets resolved_at on the unresolved note" do
+          subject.resolve!(current_user)
+
+          expect(third_note.resolved_at).not_to be_nil
+        end
+
+        it "sets resolved_by on the unresolved note" do
+          subject.resolve!(current_user)
+
+          expect(third_note.resolved_by).to eq(current_user)
+        end
+
+        it "marks the unresolved note as resolved" do
+          subject.resolve!(current_user)
+
+          expect(third_note.resolved?).to be true
+        end
+
+        it "sets resolved_at" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved_at).not_to be_nil
+        end
+
+        it "sets resolved_by" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved_by).to eq(current_user)
+        end
+
+        it "marks as resolved" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved?).to be true
+        end
+      end
+
+      context "when no resolvable notes are resolved" do
+        it "calls resolve! on every resolvable note" do
+          expect(first_note).to receive(:resolve!).with(current_user)
+          expect(second_note).not_to receive(:resolve!)
+          expect(third_note).to receive(:resolve!).with(current_user)
+
+          subject.resolve!(current_user)
+        end
+
+        it "sets resolved_at on the unresolved notes" do
+          subject.resolve!(current_user)
+
+          expect(first_note.resolved_at).not_to be_nil
+          expect(third_note.resolved_at).not_to be_nil
+        end
+
+        it "sets resolved_by on the unresolved notes" do
+          subject.resolve!(current_user)
+
+          expect(first_note.resolved_by).to eq(current_user)
+          expect(third_note.resolved_by).to eq(current_user)
+        end
+
+        it "marks the unresolved notes as resolved" do
+          subject.resolve!(current_user)
+
+          expect(first_note.resolved?).to be true
+          expect(third_note.resolved?).to be true
+        end
+
+        it "sets resolved_at" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved_at).not_to be_nil
+        end
+
+        it "sets resolved_by" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved_by).to eq(current_user)
+        end
+
+        it "marks as resolved" do
+          subject.resolve!(current_user)
+
+          expect(subject.resolved?).to be true
+        end
+      end
+    end
+  end
+
+  describe "#unresolve!" do
+    context "when not resolvable" do
+      before do
+        allow(subject).to receive(:resolvable?).and_return(false)
+      end
+
+      it "returns nil" do
+        expect(subject.unresolve!).to be_nil
+      end
+    end
+
+    context "when resolvable" do
+      let(:user) { create(:user) }
+
+      before do
+        allow(subject).to receive(:resolvable?).and_return(true)
+
+        allow(first_note).to receive(:resolvable?).and_return(true)
+        allow(second_note).to receive(:resolvable?).and_return(false)
+        allow(third_note).to receive(:resolvable?).and_return(true)
+      end
+
+      context "when all resolvable notes are resolved" do
+        before do
+          first_note.resolve!(user)
+          third_note.resolve!(user)
+        end
+
+        it "calls unresolve! on every resolvable note" do
+          expect(first_note).to receive(:unresolve!)
+          expect(second_note).not_to receive(:unresolve!)
+          expect(third_note).to receive(:unresolve!)
+
+          subject.unresolve!
+        end
+
+        it "unsets resolved_at on the resolved notes" do
+          subject.unresolve!
+
+          expect(first_note.resolved_at).to be_nil
+          expect(third_note.resolved_at).to be_nil
+        end
+
+        it "unsets resolved_by on the resolved notes" do
+          subject.unresolve!
+
+          expect(first_note.resolved_by).to be_nil
+          expect(third_note.resolved_by).to be_nil
+        end
+
+        it "unmarks the resolved notes as resolved" do
+          subject.unresolve!
+
+          expect(first_note.resolved?).to be false
+          expect(third_note.resolved?).to be false
+        end
+
+        it "unsets resolved_at" do
+          subject.unresolve!
+
+          expect(subject.resolved_at).to be_nil
+        end
+
+        it "unsets resolved_by" do
+          subject.unresolve!
+
+          expect(subject.resolved_by).to be_nil
+        end
+
+        it "unmarks as resolved" do
+          subject.unresolve!
+
+          expect(subject.resolved?).to be false
+        end
+      end
+
+      context "when some resolvable notes are resolved" do
+        before do
+          first_note.resolve!(user)
+        end
+
+        it "calls unresolve! on every resolvable note" do
+          expect(first_note).to receive(:unresolve!)
+          expect(second_note).not_to receive(:unresolve!)
+          expect(third_note).to receive(:unresolve!)
+
+          subject.unresolve!
+        end
+
+        it "unsets resolved_at on the resolved note" do
+          subject.unresolve!
+
+          expect(first_note.resolved_at).to be_nil
+        end
+
+        it "unsets resolved_by on the resolved note" do
+          subject.unresolve!
+
+          expect(first_note.resolved_by).to be_nil
+        end
+
+        it "unmarks the resolved note as resolved" do
+          subject.unresolve!
+
+          expect(first_note.resolved?).to be false
+        end
+      end
+
+      context "when no resolvable notes are resolved" do
+        it "calls unresolve! on every resolvable note" do
+          expect(first_note).to receive(:unresolve!)
+          expect(second_note).not_to receive(:unresolve!)
+          expect(third_note).to receive(:unresolve!)
+
+          subject.unresolve!
+        end
+      end
+    end
+  end
+
+  describe "#collapsed?" do
+    context "when a diff discussion" do
+      before do
+        allow(subject).to receive(:diff_discussion?).and_return(true)
+      end
+
+      context "when resolvable" do
+        before do
+          allow(subject).to receive(:resolvable?).and_return(true)
+        end
+
+        context "when resolved" do
+          before do
+            allow(subject).to receive(:resolved?).and_return(true)
+          end
+
+          it "returns true" do
+            expect(subject.collapsed?).to be true
+          end
+        end
+
+        context "when not resolved" do
+          before do
+            allow(subject).to receive(:resolved?).and_return(false)
+          end
+
+          it "returns false" do
+            expect(subject.collapsed?).to be false
+          end
+        end
+      end
+
+      context "when not resolvable" do
+        before do
+          allow(subject).to receive(:resolvable?).and_return(false)
+        end
+
+        context "when active" do
+          before do
+            allow(subject).to receive(:active?).and_return(true)
+          end
+
+          it "returns false" do
+            expect(subject.collapsed?).to be false
+          end
+        end
+
+        context "when outdated" do
+          before do
+            allow(subject).to receive(:active?).and_return(false)
+          end
+
+          it "returns true" do
+            expect(subject.collapsed?).to be true
+          end
+        end
+      end
+    end
+
+    context "when not a diff discussion" do
+      before do
+        allow(subject).to receive(:diff_discussion?).and_return(false)
+      end
+
+      it "returns false" do
+        expect(subject.collapsed?).to be false
+      end
+    end
+  end
+end
diff --git a/spec/models/legacy_diff_note_spec.rb b/spec/models/legacy_diff_note_spec.rb
index 2cfd26419ca..81517a18b74 100644
--- a/spec/models/legacy_diff_note_spec.rb
+++ b/spec/models/legacy_diff_note_spec.rb
@@ -73,4 +73,29 @@ describe LegacyDiffNote, models: true do
       end
     end
   end
+
+  describe "#discussion_id" do
+    let(:note) { create(:note) }
+
+    context "when it is newly created" do
+      it "has a discussion id" do
+        expect(note.discussion_id).not_to be_nil
+        expect(note.discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+
+    context "when it didn't store a discussion id before" do
+      before do
+        note.update_column(:discussion_id, nil)
+      end
+
+      it "has a discussion id" do
+        # The discussion_id is set in `after_initialize`, so `reload` won't work
+        reloaded_note = Note.find(note.id)
+
+        expect(reloaded_note.discussion_id).not_to be_nil
+        expect(reloaded_note.discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+  end
 end
diff --git a/spec/models/merge_request_spec.rb b/spec/models/merge_request_spec.rb
index f83dbefedc0..64c56d922ff 100644
--- a/spec/models/merge_request_spec.rb
+++ b/spec/models/merge_request_spec.rb
@@ -784,6 +784,98 @@ describe MergeRequest, models: true do
     end
   end
 
+  context "discussion status" do
+    let(:first_discussion) { Discussion.new([create(:diff_note_on_merge_request)]) }
+    let(:second_discussion) { Discussion.new([create(:diff_note_on_merge_request)]) }
+    let(:third_discussion) { Discussion.new([create(:diff_note_on_merge_request)]) }
+
+    before do
+      allow(subject).to receive(:diff_discussions).and_return([first_discussion, second_discussion, third_discussion])
+    end
+
+    describe "#discussions_resolvable?" do
+      context "when all discussions are unresolvable" do
+        before do
+          allow(first_discussion).to receive(:resolvable?).and_return(false)
+          allow(second_discussion).to receive(:resolvable?).and_return(false)
+          allow(third_discussion).to receive(:resolvable?).and_return(false)
+        end
+
+        it "returns false" do
+          expect(subject.discussions_resolvable?).to be false
+        end
+      end
+
+      context "when some discussions are unresolvable and some discussions are resolvable" do
+        before do
+          allow(first_discussion).to receive(:resolvable?).and_return(true)
+          allow(second_discussion).to receive(:resolvable?).and_return(false)
+          allow(third_discussion).to receive(:resolvable?).and_return(true)
+        end
+
+        it "returns true" do
+          expect(subject.discussions_resolvable?).to be true
+        end
+      end
+
+      context "when all discussions are resolvable" do
+        before do
+          allow(first_discussion).to receive(:resolvable?).and_return(true)
+          allow(second_discussion).to receive(:resolvable?).and_return(true)
+          allow(third_discussion).to receive(:resolvable?).and_return(true)
+        end
+
+        it "returns true" do
+          expect(subject.discussions_resolvable?).to be true
+        end
+      end
+    end
+
+    describe "#discussions_resolved?" do
+      context "when discussions are not resolvable" do
+        before do
+          allow(subject).to receive(:discussions_resolvable?).and_return(false)
+        end
+
+        it "returns false" do
+          expect(subject.discussions_resolved?).to be false
+        end
+      end
+
+      context "when discussions are resolvable" do
+        before do
+          allow(subject).to receive(:discussions_resolvable?).and_return(true)
+
+          allow(first_discussion).to receive(:resolvable?).and_return(true)
+          allow(second_discussion).to receive(:resolvable?).and_return(false)
+          allow(third_discussion).to receive(:resolvable?).and_return(true)
+        end
+
+        context "when all resolvable discussions are resolved" do
+          before do
+            allow(first_discussion).to receive(:resolved?).and_return(true)
+            allow(third_discussion).to receive(:resolved?).and_return(true)
+          end
+
+          it "returns true" do
+            expect(subject.discussions_resolved?).to be true
+          end
+        end
+
+        context "when some resolvable discussions are not resolved" do
+          before do
+            allow(first_discussion).to receive(:resolved?).and_return(true)
+            allow(third_discussion).to receive(:resolved?).and_return(false)
+          end
+
+          it "returns false" do
+            expect(subject.discussions_resolved?).to be false
+          end
+        end
+      end
+    end
+  end
+
   describe '#conflicts_can_be_resolved_in_ui?' do
     def create_merge_request(source_branch)
       create(:merge_request, source_branch: source_branch, target_branch: 'conflict-start') do |mr|
diff --git a/spec/models/note_spec.rb b/spec/models/note_spec.rb
index 53733d253f7..ef2747046b9 100644
--- a/spec/models/note_spec.rb
+++ b/spec/models/note_spec.rb
@@ -1,6 +1,8 @@
 require 'spec_helper'
 
 describe Note, models: true do
+  include RepoHelpers
+
   describe 'associations' do
     it { is_expected.to belong_to(:project) }
     it { is_expected.to belong_to(:noteable).touch(true) }
@@ -267,4 +269,81 @@ describe Note, models: true do
       expect(note.participants).to include(note.author)
     end
   end
+
+  describe ".grouped_diff_discussions" do
+    let!(:merge_request) { create(:merge_request) }
+    let(:project) { merge_request.project }
+    let!(:active_diff_note1) { create(:diff_note_on_merge_request, project: project, noteable: merge_request) }
+    let!(:active_diff_note2) { create(:diff_note_on_merge_request, project: project, noteable: merge_request) }
+    let!(:active_diff_note3) { create(:diff_note_on_merge_request, project: project, noteable: merge_request, position: active_position2) }
+    let!(:outdated_diff_note1) { create(:diff_note_on_merge_request, project: project, noteable: merge_request, position: outdated_position) }
+    let!(:outdated_diff_note2) { create(:diff_note_on_merge_request, project: project, noteable: merge_request, position: outdated_position) }
+
+    let(:active_position2) do
+      Gitlab::Diff::Position.new(
+        old_path: "files/ruby/popen.rb",
+        new_path: "files/ruby/popen.rb",
+        old_line: 16,
+        new_line: 22,
+        diff_refs: merge_request.diff_refs
+      )
+    end
+
+    let(:outdated_position) do
+      Gitlab::Diff::Position.new(
+        old_path: "files/ruby/popen.rb",
+        new_path: "files/ruby/popen.rb",
+        old_line: nil,
+        new_line: 9,
+        diff_refs: project.commit("874797c3a73b60d2187ed6e2fcabd289ff75171e").diff_refs
+      )
+    end
+
+    subject { merge_request.notes.grouped_diff_discussions }
+
+    it "includes active discussions" do
+      discussions = subject.values
+
+      expect(discussions.count).to eq(2)
+      expect(discussions.map(&:id)).to eq([active_diff_note1.discussion_id, active_diff_note3.discussion_id])
+      expect(discussions.all?(&:active?)).to be true
+
+      expect(discussions.first.notes).to eq([active_diff_note1, active_diff_note2])
+      expect(discussions.last.notes).to eq([active_diff_note3])
+    end
+
+    it "doesn't include outdated discussions" do
+      expect(subject.values.map(&:id)).not_to include(outdated_diff_note1.discussion_id)
+    end
+
+    it "groups the discussions by line code" do
+      expect(subject[active_diff_note1.line_code].id).to eq(active_diff_note1.discussion_id)
+      expect(subject[active_diff_note3.line_code].id).to eq(active_diff_note3.discussion_id)
+    end
+  end
+
+  describe "#discussion_id" do
+    let(:note) { create(:note) }
+
+    context "when it is newly created" do
+      it "has a discussion id" do
+        expect(note.discussion_id).not_to be_nil
+        expect(note.discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+
+    context "when it didn't store a discussion id before" do
+      before do
+        note.update_column(:discussion_id, nil)
+      end
+
+      it "has a discussion id" do
+        # The discussion_id is set in `after_initialize`, so `reload` won't work
+        reloaded_note = Note.find(note.id)
+
+        expect(reloaded_note.discussion_id).not_to be_nil
+        expect(reloaded_note.discussion_id).to match(/\A\h{40}\z/)
+      end
+    end
+  end
 end
diff --git a/spec/services/merge_requests/resolved_discussion_notification_service.rb b/spec/services/merge_requests/resolved_discussion_notification_service.rb
new file mode 100644
index 00000000000..7ddd812e513
--- /dev/null
+++ b/spec/services/merge_requests/resolved_discussion_notification_service.rb
@@ -0,0 +1,46 @@
+require 'spec_helper'
+
+describe MergeRequests::ResolvedDiscussionNotificationService, services: true do
+  let(:merge_request) { create(:merge_request) }
+  let(:user) { create(:user) }
+  let(:project) { merge_request.project }
+  subject { described_class.new(project, user) }
+
+  describe "#execute" do
+    context "when not all discussions are resolved" do
+      before do
+        allow(merge_request).to receive(:discussions_resolved?).and_return(false)
+      end
+
+      it "doesn't add a system note" do
+        expect(SystemNoteService).not_to receive(:resolve_all_discussions)
+
+        subject.execute(merge_request)
+      end
+
+      it "doesn't send a notification email" do
+        expect_any_instance_of(NotificationService).not_to receive(:resolve_all_discussions)
+
+        subject.execute(merge_request)
+      end
+    end
+
+    context "when all discussions are resolved" do
+      before do
+        allow(merge_request).to receive(:discussions_resolved?).and_return(true)
+      end
+
+      it "adds a system note" do
+        expect(SystemNoteService).to receive(:resolve_all_discussions).with(merge_request, project, user)
+
+        subject.execute(merge_request)
+      end
+
+      it "sends a notification email" do
+        expect_any_instance_of(NotificationService).to receive(:resolve_all_discussions).with(merge_request, user)
+
+        subject.execute(merge_request)
+      end
+    end
+  end
+end
diff --git a/spec/services/notification_service_spec.rb b/spec/services/notification_service_spec.rb
index 62c97e09288..18da3b1b453 100644
--- a/spec/services/notification_service_spec.rb
+++ b/spec/services/notification_service_spec.rb
@@ -1042,6 +1042,52 @@ describe NotificationService, services: true do
         end
       end
     end
+
+    describe "#resolve_all_discussions" do
+      it do
+        notification.resolve_all_discussions(merge_request, @u_disabled)
+
+        should_email(merge_request.assignee)
+        should_email(@u_watcher)
+        should_email(@u_participant_mentioned)
+        should_email(@subscriber)
+        should_email(@watcher_and_subscriber)
+        should_email(@u_guest_watcher)
+        should_not_email(@unsubscriber)
+        should_not_email(@u_participating)
+        should_not_email(@u_disabled)
+        should_not_email(@u_lazy_participant)
+      end
+
+      context 'participating' do
+        context 'by assignee' do
+          before do
+            merge_request.update_attribute(:assignee, @u_lazy_participant)
+            notification.resolve_all_discussions(merge_request, @u_disabled)
+          end
+
+          it { should_email(@u_lazy_participant) }
+        end
+
+        context 'by note' do
+          let!(:note) { create(:note_on_issue, noteable: merge_request, project_id: project.id, note: 'anything', author: @u_lazy_participant) }
+
+          before { notification.resolve_all_discussions(merge_request, @u_disabled) }
+
+          it { should_email(@u_lazy_participant) }
+        end
+
+        context 'by author' do
+          before do
+            merge_request.author = @u_lazy_participant
+            merge_request.save
+            notification.resolve_all_discussions(merge_request, @u_disabled)
+          end
+
+          it { should_email(@u_lazy_participant) }
+        end
+      end
+    end
   end
 
   describe 'Projects' do