Merge branch 'tz-ide-open-mr' into 'master'

Basic Setup for MR Showing

Closes #44840 and #44839

See merge request gitlab-org/gitlab-ce!17952

28 files changed, 754 insertions, 392 deletions

diff --git a/app/assets/javascripts/api.js b/app/assets/javascripts/api.js
index cbcefb2c18f..8ad3d18b302 100644
--- a/app/assets/javascripts/api.js
+++ b/app/assets/javascripts/api.js
@@ -10,6 +10,9 @@ const Api = {
   projectsPath: '/api/:version/projects.json',
   projectPath: '/api/:version/projects/:id',
   projectLabelsPath: '/:namespace_path/:project_path/labels',
+  mergeRequestPath: '/api/:version/projects/:id/merge_requests/:mrid',
+  mergeRequestChangesPath: '/api/:version/projects/:id/merge_requests/:mrid/changes',
+  mergeRequestVersionsPath: '/api/:version/projects/:id/merge_requests/:mrid/versions',
   groupLabelsPath: '/groups/:namespace_path/-/labels',
   licensePath: '/api/:version/templates/licenses/:key',
   gitignorePath: '/api/:version/templates/gitignores/:key',
@@ -22,25 +25,27 @@ const Api = {
   createBranchPath: '/api/:version/projects/:id/repository/branches',
 
   group(groupId, callback) {
-    const url = Api.buildUrl(Api.groupPath)
-      .replace(':id', groupId);
-    return axios.get(url)
-      .then(({ data }) => {
-        callback(data);
+    const url = Api.buildUrl(Api.groupPath).replace(':id', groupId);
+    return axios.get(url).then(({ data }) => {
+      callback(data);
 
-        return data;
-      });
+      return data;
+    });
   },
 
   // Return groups list. Filtered by query
   groups(query, options, callback = $.noop) {
     const url = Api.buildUrl(Api.groupsPath);
-    return axios.get(url, {
-      params: Object.assign({
-        search: query,
-        per_page: 20,
-      }, options),
-    })
+    return axios
+      .get(url, {
+        params: Object.assign(
+          {
+            search: query,
+            per_page: 20,
+          },
+          options,
+        ),
+      })
       .then(({ data }) => {
         callback(data);
 
@@ -51,12 +56,13 @@ const Api = {
   // Return namespaces list. Filtered by query
   namespaces(query, callback) {
     const url = Api.buildUrl(Api.namespacesPath);
-    return axios.get(url, {
-      params: {
-        search: query,
-        per_page: 20,
-      },
-    })
+    return axios
+      .get(url, {
+        params: {
+          search: query,
+          per_page: 20,
+        },
+      })
       .then(({ data }) => callback(data));
   },
 
@@ -73,9 +79,10 @@ const Api = {
       defaults.membership = true;
     }
 
-    return axios.get(url, {
-      params: Object.assign(defaults, options),
-    })
+    return axios
+      .get(url, {
+        params: Object.assign(defaults, options),
+      })
       .then(({ data }) => {
         callback(data);
 
@@ -85,8 +92,32 @@ const Api = {
 
   // Return single project
   project(projectPath) {
-    const url = Api.buildUrl(Api.projectPath)
-            .replace(':id', encodeURIComponent(projectPath));
+    const url = Api.buildUrl(Api.projectPath).replace(':id', encodeURIComponent(projectPath));
+
+    return axios.get(url);
+  },
+
+  // Return Merge Request for project
+  mergeRequest(projectPath, mergeRequestId) {
+    const url = Api.buildUrl(Api.mergeRequestPath)
+      .replace(':id', encodeURIComponent(projectPath))
+      .replace(':mrid', mergeRequestId);
+
+    return axios.get(url);
+  },
+
+  mergeRequestChanges(projectPath, mergeRequestId) {
+    const url = Api.buildUrl(Api.mergeRequestChangesPath)
+      .replace(':id', encodeURIComponent(projectPath))
+      .replace(':mrid', mergeRequestId);
+
+    return axios.get(url);
+  },
+
+  mergeRequestVersions(projectPath, mergeRequestId) {
+    const url = Api.buildUrl(Api.mergeRequestVersionsPath)
+      .replace(':id', encodeURIComponent(projectPath))
+      .replace(':mrid', mergeRequestId);
 
     return axios.get(url);
   },
@@ -102,30 +133,30 @@ const Api = {
       url = Api.buildUrl(Api.groupLabelsPath).replace(':namespace_path', namespacePath);
     }
 
-    return axios.post(url, {
-      label: data,
-    })
+    return axios
+      .post(url, {
+        label: data,
+      })
       .then(res => callback(res.data))
       .catch(e => callback(e.response.data));
   },
 
   // Return group projects list. Filtered by query
   groupProjects(groupId, query, callback) {
-    const url = Api.buildUrl(Api.groupProjectsPath)
-      .replace(':id', groupId);
-    return axios.get(url, {
-      params: {
-        search: query,
-        per_page: 20,
-      },
-    })
+    const url = Api.buildUrl(Api.groupProjectsPath).replace(':id', groupId);
+    return axios
+      .get(url, {
+        params: {
+          search: query,
+          per_page: 20,
+        },
+      })
       .then(({ data }) => callback(data));
   },
 
   commitMultiple(id, data) {
     // see https://docs.gitlab.com/ce/api/commits.html#create-a-commit-with-multiple-files-and-actions
-    const url = Api.buildUrl(Api.commitPath)
-      .replace(':id', encodeURIComponent(id));
+    const url = Api.buildUrl(Api.commitPath).replace(':id', encodeURIComponent(id));
     return axios.post(url, JSON.stringify(data), {
       headers: {
         'Content-Type': 'application/json; charset=utf-8',
@@ -136,39 +167,34 @@ const Api = {
   branchSingle(id, branch) {
     const url = Api.buildUrl(Api.branchSinglePath)
       .replace(':id', encodeURIComponent(id))
-      .replace(':branch', branch);
+      .replace(':branch', encodeURIComponent(branch));
 
     return axios.get(url);
   },
 
   // Return text for a specific license
   licenseText(key, data, callback) {
-    const url = Api.buildUrl(Api.licensePath)
-      .replace(':key', key);
-    return axios.get(url, {
-      params: data,
-    })
+    const url = Api.buildUrl(Api.licensePath).replace(':key', key);
+    return axios
+      .get(url, {
+        params: data,
+      })
       .then(res => callback(res.data));
   },
 
   gitignoreText(key, callback) {
-    const url = Api.buildUrl(Api.gitignorePath)
-      .replace(':key', key);
-    return axios.get(url)
-      .then(({ data }) => callback(data));
+    const url = Api.buildUrl(Api.gitignorePath).replace(':key', key);
+    return axios.get(url).then(({ data }) => callback(data));
   },
 
   gitlabCiYml(key, callback) {
-    const url = Api.buildUrl(Api.gitlabCiYmlPath)
-      .replace(':key', key);
-    return axios.get(url)
-      .then(({ data }) => callback(data));
+    const url = Api.buildUrl(Api.gitlabCiYmlPath).replace(':key', key);
+    return axios.get(url).then(({ data }) => callback(data));
   },
 
   dockerfileYml(key, callback) {
     const url = Api.buildUrl(Api.dockerfilePath).replace(':key', key);
-    return axios.get(url)
-      .then(({ data }) => callback(data));
+    return axios.get(url).then(({ data }) => callback(data));
   },
 
   issueTemplate(namespacePath, projectPath, key, type, callback) {
@@ -177,7 +203,8 @@ const Api = {
       .replace(':type', type)
       .replace(':project_path', projectPath)
       .replace(':namespace_path', namespacePath);
-    return axios.get(url)
+    return axios
+      .get(url)
       .then(({ data }) => callback(null, data))
       .catch(callback);
   },
@@ -185,10 +212,13 @@ const Api = {
   users(query, options) {
     const url = Api.buildUrl(this.usersPath);
     return axios.get(url, {
-      params: Object.assign({
-        search: query,
-        per_page: 20,
-      }, options),
+      params: Object.assign(
+        {
+          search: query,
+          per_page: 20,
+        },
+        options,
+      ),
     });
   },
 
diff --git a/app/assets/javascripts/ide/components/changed_file_icon.vue b/app/assets/javascripts/ide/components/changed_file_icon.vue
index 0c54c992e51..037e3efb4ce 100644
--- a/app/assets/javascripts/ide/components/changed_file_icon.vue
+++ b/app/assets/javascripts/ide/components/changed_file_icon.vue
@@ -1,25 +1,25 @@
 <script>
-  import icon from '~/vue_shared/components/icon.vue';
+import icon from '~/vue_shared/components/icon.vue';
 
-  export default {
-    components: {
-      icon,
+export default {
+  components: {
+    icon,
+  },
+  props: {
+    file: {
+      type: Object,
+      required: true,
     },
-    props: {
-      file: {
-        type: Object,
-        required: true,
-      },
+  },
+  computed: {
+    changedIcon() {
+      return this.file.tempFile ? 'file-addition' : 'file-modified';
     },
-    computed: {
-      changedIcon() {
-        return this.file.tempFile ? 'file-addition' : 'file-modified';
-      },
-      changedIconClass() {
-        return `multi-${this.changedIcon}`;
-      },
+    changedIconClass() {
+      return `multi-${this.changedIcon}`;
     },
-  };
+  },
+};
 </script>
 
 <template>
diff --git a/app/assets/javascripts/ide/components/editor_mode_dropdown.vue b/app/assets/javascripts/ide/components/editor_mode_dropdown.vue
index 170347881e0..0c44a755f56 100644
--- a/app/assets/javascripts/ide/components/editor_mode_dropdown.vue
+++ b/app/assets/javascripts/ide/components/editor_mode_dropdown.vue
@@ -1,31 +1,44 @@
 <script>
-  import Icon from '~/vue_shared/components/icon.vue';
+import Icon from '~/vue_shared/components/icon.vue';
+import { __, sprintf } from '~/locale';
 
-  export default {
-    components: {
-      Icon,
+export default {
+  components: {
+    Icon,
+  },
+  props: {
+    hasChanges: {
+      type: Boolean,
+      required: false,
+      default: false,
     },
-    props: {
-      hasChanges: {
-        type: Boolean,
-        required: false,
-        default: false,
-      },
-      viewer: {
-        type: String,
-        required: true,
-      },
-      showShadow: {
-        type: Boolean,
-        required: true,
-      },
+    mergeRequestId: {
+      type: String,
+      required: false,
+      default: '',
     },
-    methods: {
-      changeMode(mode) {
-        this.$emit('click', mode);
-      },
+    viewer: {
+      type: String,
+      required: true,
     },
-  };
+    showShadow: {
+      type: Boolean,
+      required: true,
+    },
+  },
+  computed: {
+    mergeReviewLine() {
+      return sprintf(__('Reviewing (merge request !%{mergeRequestId})'), {
+        mergeRequestId: this.mergeRequestId,
+      });
+    },
+  },
+  methods: {
+    changeMode(mode) {
+      this.$emit('click', mode);
+    },
+  },
+};
 </script>
 
 <template>
@@ -43,7 +56,10 @@
       }"
       data-toggle="dropdown"
     >
-      <template v-if="viewer === 'editor'">
+      <template v-if="viewer === 'mrdiff' && mergeRequestId">
+        {{ mergeReviewLine }}
+      </template>
+      <template v-else-if="viewer === 'editor'">
         {{ __('Editing') }}
       </template>
       <template v-else>
@@ -57,6 +73,29 @@
     </button>
     <div class="dropdown-menu dropdown-menu-selectable dropdown-open-left">
       <ul>
+        <template v-if="mergeRequestId">
+          <li>
+            <a
+              href="#"
+              @click.prevent="changeMode('mrdiff')"
+              :class="{
+                'is-active': viewer === 'mrdiff',
+              }"
+            >
+              <strong class="dropdown-menu-inner-title">
+                {{ mergeReviewLine }}
+              </strong>
+              <span class="dropdown-menu-inner-content">
+                {{ __('Compare changes with the merge request target branch') }}
+              </span>
+            </a>
+          </li>
+          <li
+            role="separator"
+            class="divider"
+          >
+          </li>
+        </template>
         <li>
           <a
             href="#"
diff --git a/app/assets/javascripts/ide/components/ide.vue b/app/assets/javascripts/ide/components/ide.vue
index 015e750525a..5e44af01241 100644
--- a/app/assets/javascripts/ide/components/ide.vue
+++ b/app/assets/javascripts/ide/components/ide.vue
@@ -1,51 +1,51 @@
 <script>
-  import { mapState, mapGetters } from 'vuex';
-  import ideSidebar from './ide_side_bar.vue';
-  import ideContextbar from './ide_context_bar.vue';
-  import repoTabs from './repo_tabs.vue';
-  import repoFileButtons from './repo_file_buttons.vue';
-  import ideStatusBar from './ide_status_bar.vue';
-  import repoEditor from './repo_editor.vue';
+import { mapState, mapGetters } from 'vuex';
+import ideSidebar from './ide_side_bar.vue';
+import ideContextbar from './ide_context_bar.vue';
+import repoTabs from './repo_tabs.vue';
+import repoFileButtons from './repo_file_buttons.vue';
+import ideStatusBar from './ide_status_bar.vue';
+import repoEditor from './repo_editor.vue';
 
-  export default {
-    components: {
-      ideSidebar,
-      ideContextbar,
-      repoTabs,
-      repoFileButtons,
-      ideStatusBar,
-      repoEditor,
+export default {
+  components: {
+    ideSidebar,
+    ideContextbar,
+    repoTabs,
+    repoFileButtons,
+    ideStatusBar,
+    repoEditor,
+  },
+  props: {
+    emptyStateSvgPath: {
+      type: String,
+      required: true,
     },
-    props: {
-      emptyStateSvgPath: {
-        type: String,
-        required: true,
-      },
-      noChangesStateSvgPath: {
-        type: String,
-        required: true,
-      },
-      committedStateSvgPath: {
-        type: String,
-        required: true,
-      },
+    noChangesStateSvgPath: {
+      type: String,
+      required: true,
     },
-    computed: {
-      ...mapState(['changedFiles', 'openFiles', 'viewer']),
-      ...mapGetters(['activeFile', 'hasChanges']),
+    committedStateSvgPath: {
+      type: String,
+      required: true,
     },
-    mounted() {
-      const returnValue = 'Are you sure you want to lose unsaved changes?';
-      window.onbeforeunload = e => {
-        if (!this.changedFiles.length) return undefined;
+  },
+  computed: {
+    ...mapState(['changedFiles', 'openFiles', 'viewer', 'currentMergeRequestId']),
+    ...mapGetters(['activeFile', 'hasChanges']),
+  },
+  mounted() {
+    const returnValue = 'Are you sure you want to lose unsaved changes?';
+    window.onbeforeunload = e => {
+      if (!this.changedFiles.length) return undefined;
 
-        Object.assign(e, {
-          returnValue,
-        });
-        return returnValue;
-      };
-    },
-  };
+      Object.assign(e, {
+        returnValue,
+      });
+      return returnValue;
+    };
+  },
+};
 </script>
 
 <template>
@@ -63,6 +63,7 @@
           :files="openFiles"
           :viewer="viewer"
           :has-changes="hasChanges"
+          :merge-request-id="currentMergeRequestId"
         />
         <repo-editor
           class="multi-file-edit-pane-content"
diff --git a/app/assets/javascripts/ide/components/mr_file_icon.vue b/app/assets/javascripts/ide/components/mr_file_icon.vue
new file mode 100644
index 00000000000..8a440902dfc
--- /dev/null
+++ b/app/assets/javascripts/ide/components/mr_file_icon.vue
@@ -0,0 +1,23 @@
+<script>
+import icon from '~/vue_shared/components/icon.vue';
+import tooltip from '~/vue_shared/directives/tooltip';
+
+export default {
+  components: {
+    icon,
+  },
+  directives: {
+    tooltip,
+  },
+};
+</script>
+
+<template>
+  <icon
+    name="git-merge"
+    v-tooltip
+    title="__('Part of merge request changes')"
+    css-classes="ide-file-changed-icon"
+    :size="12"
+  />
+</template>
diff --git a/app/assets/javascripts/ide/components/repo_editor.vue b/app/assets/javascripts/ide/components/repo_editor.vue
index e73d1ce839f..b6f8f8a1c99 100644
--- a/app/assets/javascripts/ide/components/repo_editor.vue
+++ b/app/assets/javascripts/ide/components/repo_editor.vue
@@ -1,6 +1,6 @@
 <script>
 /* global monaco */
-import { mapState, mapActions } from 'vuex';
+import { mapState, mapGetters, mapActions } from 'vuex';
 import flash from '~/flash';
 import monacoLoader from '../monaco_loader';
 import Editor from '../lib/editor';
@@ -13,12 +13,8 @@ export default {
     },
   },
   computed: {
-    ...mapState([
-      'leftPanelCollapsed',
-      'rightPanelCollapsed',
-      'viewer',
-      'delayViewerUpdated',
-    ]),
+    ...mapState(['leftPanelCollapsed', 'rightPanelCollapsed', 'viewer', 'delayViewerUpdated']),
+    ...mapGetters(['currentMergeRequest']),
     shouldHideEditor() {
       return this.file && this.file.binary && !this.file.raw;
     },
@@ -68,9 +64,14 @@ export default {
 
       this.editor.clearEditor();
 
-      this.getRawFileData(this.file)
+      this.getRawFileData({
+        path: this.file.path,
+        baseSha: this.currentMergeRequest ? this.currentMergeRequest.baseCommitSha : '',
+      })
         .then(() => {
-          const viewerPromise = this.delayViewerUpdated ? this.updateViewer('editor') : Promise.resolve();
+          const viewerPromise = this.delayViewerUpdated
+            ? this.updateViewer('editor')
+            : Promise.resolve();
 
           return viewerPromise;
         })
@@ -78,7 +79,7 @@ export default {
           this.updateDelayViewerUpdated(false);
           this.createEditorInstance();
         })
-        .catch((err) => {
+        .catch(err => {
           flash('Error setting up monaco. Please try again.', 'alert', document, null, false, true);
           throw err;
         });
@@ -101,9 +102,13 @@ export default {
 
       this.model = this.editor.createModel(this.file);
 
-      this.editor.attachModel(this.model);
+      if (this.viewer === 'mrdiff') {
+        this.editor.attachMergeRequestModel(this.model);
+      } else {
+        this.editor.attachModel(this.model);
+      }
 
-      this.model.onChange((model) => {
+      this.model.onChange(model => {
         const { file } = model;
 
         if (file.active) {
diff --git a/app/assets/javascripts/ide/components/repo_file.vue b/app/assets/javascripts/ide/components/repo_file.vue
index 297b9c2628f..1935ee1a4bb 100644
--- a/app/assets/javascripts/ide/components/repo_file.vue
+++ b/app/assets/javascripts/ide/components/repo_file.vue
@@ -6,6 +6,7 @@ import router from '../ide_router';
 import newDropdown from './new_dropdown/index.vue';
 import fileStatusIcon from './repo_file_status_icon.vue';
 import changedFileIcon from './changed_file_icon.vue';
+import mrFileIcon from './mr_file_icon.vue';
 
 export default {
   name: 'RepoFile',
@@ -15,6 +16,7 @@ export default {
     fileStatusIcon,
     fileIcon,
     changedFileIcon,
+    mrFileIcon,
   },
   props: {
     file: {
@@ -56,10 +58,7 @@ export default {
     ...mapActions(['toggleTreeOpen', 'updateDelayViewerUpdated']),
     clickFile() {
       // Manual Action if a tree is selected/opened
-      if (
-        this.isTree &&
-        this.$router.currentRoute.path === `/project${this.file.url}`
-      ) {
+      if (this.isTree && this.$router.currentRoute.path === `/project${this.file.url}`) {
         this.toggleTreeOpen(this.file.path);
       }
 
@@ -102,11 +101,15 @@ export default {
             :file="file"
           />
         </span>
-        <changed-file-icon
-          :file="file"
-          v-if="file.changed || file.tempFile"
-          class="prepend-top-5 pull-right"
-        />
+        <span class="pull-right">
+          <mr-file-icon
+            v-if="file.mrChange"
+          />
+          <changed-file-icon
+            :file="file"
+            v-if="file.changed || file.tempFile"
+          />
+        </span>
         <new-dropdown
           v-if="isTree"
           :project-id="file.projectId"
diff --git a/app/assets/javascripts/ide/components/repo_file_status_icon.vue b/app/assets/javascripts/ide/components/repo_file_status_icon.vue
index 25d311142d5..97589e116c5 100644
--- a/app/assets/javascripts/ide/components/repo_file_status_icon.vue
+++ b/app/assets/javascripts/ide/components/repo_file_status_icon.vue
@@ -1,27 +1,27 @@
 <script>
-  import icon from '~/vue_shared/components/icon.vue';
-  import tooltip from '~/vue_shared/directives/tooltip';
-  import '~/lib/utils/datetime_utility';
+import icon from '~/vue_shared/components/icon.vue';
+import tooltip from '~/vue_shared/directives/tooltip';
+import '~/lib/utils/datetime_utility';
 
-  export default {
-    components: {
-      icon,
+export default {
+  components: {
+    icon,
+  },
+  directives: {
+    tooltip,
+  },
+  props: {
+    file: {
+      type: Object,
+      required: true,
     },
-    directives: {
-      tooltip,
+  },
+  computed: {
+    lockTooltip() {
+      return `Locked by ${this.file.file_lock.user.name}`;
     },
-    props: {
-      file: {
-        type: Object,
-        required: true,
-      },
-    },
-    computed: {
-      lockTooltip() {
-        return `Locked by ${this.file.file_lock.user.name}`;
-      },
-    },
-  };
+  },
+};
 </script>
 
 <template>
diff --git a/app/assets/javascripts/ide/components/repo_tabs.vue b/app/assets/javascripts/ide/components/repo_tabs.vue
index 8ea64ddf84a..a44e418b2eb 100644
--- a/app/assets/javascripts/ide/components/repo_tabs.vue
+++ b/app/assets/javascripts/ide/components/repo_tabs.vue
@@ -1,42 +1,46 @@
 <script>
-  import { mapActions } from 'vuex';
-  import RepoTab from './repo_tab.vue';
-  import EditorMode from './editor_mode_dropdown.vue';
+import { mapActions } from 'vuex';
+import RepoTab from './repo_tab.vue';
+import EditorMode from './editor_mode_dropdown.vue';
 
-  export default {
-    components: {
-      RepoTab,
-      EditorMode,
+export default {
+  components: {
+    RepoTab,
+    EditorMode,
+  },
+  props: {
+    files: {
+      type: Array,
+      required: true,
     },
-    props: {
-      files: {
-        type: Array,
-        required: true,
-      },
-      viewer: {
-        type: String,
-        required: true,
-      },
-      hasChanges: {
-        type: Boolean,
-        required: true,
-      },
+    viewer: {
+      type: String,
+      required: true,
     },
-    data() {
-      return {
-        showShadow: false,
-      };
+    hasChanges: {
+      type: Boolean,
+      required: true,
     },
-    updated() {
-      if (!this.$refs.tabsScroller) return;
-
-      this.showShadow =
-        this.$refs.tabsScroller.scrollWidth > this.$refs.tabsScroller.offsetWidth;
-    },
-    methods: {
-      ...mapActions(['updateViewer']),
+    mergeRequestId: {
+      type: String,
+      required: false,
+      default: '',
     },
-  };
+  },
+  data() {
+    return {
+      showShadow: false,
+    };
+  },
+  updated() {
+    if (!this.$refs.tabsScroller) return;
+
+    this.showShadow = this.$refs.tabsScroller.scrollWidth > this.$refs.tabsScroller.offsetWidth;
+  },
+  methods: {
+    ...mapActions(['updateViewer']),
+  },
+};
 </script>
 
 <template>
@@ -55,6 +59,7 @@
       :viewer="viewer"
       :show-shadow="showShadow"
       :has-changes="hasChanges"
+      :merge-request-id="mergeRequestId"
       @click="updateViewer"
     />
   </div>
diff --git a/app/assets/javascripts/ide/ide_router.js b/app/assets/javascripts/ide/ide_router.js
index db89c1d44db..be2c12c0487 100644
--- a/app/assets/javascripts/ide/ide_router.js
+++ b/app/assets/javascripts/ide/ide_router.js
@@ -44,7 +44,7 @@ const router = new VueRouter({
           component: EmptyRouterComponent,
         },
         {
-          path: 'mr/:mrid',
+          path: 'merge_requests/:mrid',
           component: EmptyRouterComponent,
         },
       ],
@@ -76,9 +76,7 @@ router.beforeEach((to, from, next) => {
             .then(() => {
               if (to.params[0]) {
                 const path =
-                  to.params[0].slice(-1) === '/'
-                    ? to.params[0].slice(0, -1)
-                    : to.params[0];
+                  to.params[0].slice(-1) === '/' ? to.params[0].slice(0, -1) : to.params[0];
                 const treeEntry = store.state.entries[path];
                 if (treeEntry) {
                   store.dispatch('handleTreeEntryAction', treeEntry);
@@ -96,6 +94,60 @@ router.beforeEach((to, from, next) => {
               );
               throw e;
             });
+        } else if (to.params.mrid) {
+          store.dispatch('updateViewer', 'mrdiff');
+
+          store
+            .dispatch('getMergeRequestData', {
+              projectId: fullProjectId,
+              mergeRequestId: to.params.mrid,
+            })
+            .then(mr => {
+              store.dispatch('getBranchData', {
+                projectId: fullProjectId,
+                branchId: mr.source_branch,
+              });
+
+              return store.dispatch('getFiles', {
+                projectId: fullProjectId,
+                branchId: mr.source_branch,
+              });
+            })
+            .then(() =>
+              store.dispatch('getMergeRequestVersions', {
+                projectId: fullProjectId,
+                mergeRequestId: to.params.mrid,
+              }),
+            )
+            .then(() =>
+              store.dispatch('getMergeRequestChanges', {
+                projectId: fullProjectId,
+                mergeRequestId: to.params.mrid,
+              }),
+            )
+            .then(mrChanges => {
+              mrChanges.changes.forEach((change, ind) => {
+                const changeTreeEntry = store.state.entries[change.new_path];
+
+                if (changeTreeEntry) {
+                  store.dispatch('setFileMrChange', {
+                    file: changeTreeEntry,
+                    mrChange: change,
+                  });
+
+                  if (ind < 10) {
+                    store.dispatch('getFileData', {
+                      path: change.new_path,
+                      makeFileActive: ind === 0,
+                    });
+                  }
+                }
+              });
+            })
+            .catch(e => {
+              flash('Error while loading the merge request. Please try again.');
+              throw e;
+            });
         }
       })
       .catch(e => {
diff --git a/app/assets/javascripts/ide/lib/common/model.js b/app/assets/javascripts/ide/lib/common/model.js
index 73cd684351c..d372c2aaad8 100644
--- a/app/assets/javascripts/ide/lib/common/model.js
+++ b/app/assets/javascripts/ide/lib/common/model.js
@@ -21,6 +21,15 @@ export default class Model {
         new this.monaco.Uri(null, null, this.file.path),
       )),
     );
+    if (this.file.mrChange) {
+      this.disposable.add(
+        (this.baseModel = this.monaco.editor.createModel(
+          this.file.baseRaw,
+          undefined,
+          new this.monaco.Uri(null, null, `target/${this.file.path}`),
+        )),
+      );
+    }
 
     this.events = new Map();
 
@@ -28,10 +37,7 @@ export default class Model {
     this.dispose = this.dispose.bind(this);
 
     eventHub.$on(`editor.update.model.dispose.${this.file.path}`, this.dispose);
-    eventHub.$on(
-      `editor.update.model.content.${this.file.path}`,
-      this.updateContent,
-    );
+    eventHub.$on(`editor.update.model.content.${this.file.path}`, this.updateContent);
   }
 
   get url() {
@@ -58,6 +64,10 @@ export default class Model {
     return this.originalModel;
   }
 
+  getBaseModel() {
+    return this.baseModel;
+  }
+
   setValue(value) {
     this.getModel().setValue(value);
   }
@@ -78,13 +88,7 @@ export default class Model {
     this.disposable.dispose();
     this.events.clear();
 
-    eventHub.$off(
-      `editor.update.model.dispose.${this.file.path}`,
-      this.dispose,
-    );
-    eventHub.$off(
-      `editor.update.model.content.${this.file.path}`,
-      this.updateContent,
-    );
+    eventHub.$off(`editor.update.model.dispose.${this.file.path}`, this.dispose);
+    eventHub.$off(`editor.update.model.content.${this.file.path}`, this.updateContent);
   }
 }
diff --git a/app/assets/javascripts/ide/lib/editor.js b/app/assets/javascripts/ide/lib/editor.js
index 887dd7e39b1..6b4ba30e086 100644
--- a/app/assets/javascripts/ide/lib/editor.js
+++ b/app/assets/javascripts/ide/lib/editor.js
@@ -109,11 +109,19 @@ export default class Editor {
     if (this.dirtyDiffController) this.dirtyDiffController.reDecorate(model);
   }
 
+  attachMergeRequestModel(model) {
+    this.instance.setModel({
+      original: model.getBaseModel(),
+      modified: model.getModel(),
+    });
+
+    this.monaco.editor.createDiffNavigator(this.instance, {
+      alwaysRevealFirst: true,
+    });
+  }
+
   setupMonacoTheme() {
-    this.monaco.editor.defineTheme(
-      gitlabTheme.themeName,
-      gitlabTheme.monacoTheme,
-    );
+    this.monaco.editor.defineTheme(gitlabTheme.themeName, gitlabTheme.monacoTheme);
 
     this.monaco.editor.setTheme('gitlab');
   }
@@ -161,8 +169,6 @@ export default class Editor {
   onPositionChange(cb) {
     if (!this.instance.onDidChangeCursorPosition) return;
 
-    this.disposable.add(
-      this.instance.onDidChangeCursorPosition(e => cb(this.instance, e)),
-    );
+    this.disposable.add(this.instance.onDidChangeCursorPosition(e => cb(this.instance, e)));
   }
 }
diff --git a/app/assets/javascripts/ide/services/index.js b/app/assets/javascripts/ide/services/index.js
index 5f1fb6cf843..a12e637616a 100644
--- a/app/assets/javascripts/ide/services/index.js
+++ b/app/assets/javascripts/ide/services/index.js
@@ -20,12 +20,35 @@ export default {
       return Promise.resolve(file.raw);
     }
 
-    return Vue.http.get(file.rawPath, { params: { format: 'json' } })
+    return Vue.http.get(file.rawPath, { params: { format: 'json' } }).then(res => res.text());
+  },
+  getBaseRawFileData(file, sha) {
+    if (file.tempFile) {
+      return Promise.resolve(file.baseRaw);
+    }
+
+    if (file.baseRaw) {
+      return Promise.resolve(file.baseRaw);
+    }
+
+    return Vue.http
+      .get(file.rawPath.replace(`/raw/${file.branchId}/${file.path}`, `/raw/${sha}/${file.path}`), {
+        params: { format: 'json' },
+      })
       .then(res => res.text());
   },
   getProjectData(namespace, project) {
     return Api.project(`${namespace}/${project}`);
   },
+  getProjectMergeRequestData(projectId, mergeRequestId) {
+    return Api.mergeRequest(projectId, mergeRequestId);
+  },
+  getProjectMergeRequestChanges(projectId, mergeRequestId) {
+    return Api.mergeRequestChanges(projectId, mergeRequestId);
+  },
+  getProjectMergeRequestVersions(projectId, mergeRequestId) {
+    return Api.mergeRequestVersions(projectId, mergeRequestId);
+  },
   getBranchData(projectId, currentBranchId) {
     return Api.branchSingle(projectId, currentBranchId);
   },
diff --git a/app/assets/javascripts/ide/stores/actions.js b/app/assets/javascripts/ide/stores/actions.js
index 7e920aa9f30..0a74f4f8925 100644
--- a/app/assets/javascripts/ide/stores/actions.js
+++ b/app/assets/javascripts/ide/stores/actions.js
@@ -6,8 +6,7 @@ import FilesDecoratorWorker from './workers/files_decorator_worker';
 
 export const redirectToUrl = (_, url) => visitUrl(url);
 
-export const setInitialData = ({ commit }, data) =>
-  commit(types.SET_INITIAL_DATA, data);
+export const setInitialData = ({ commit }, data) => commit(types.SET_INITIAL_DATA, data);
 
 export const discardAllChanges = ({ state, commit, dispatch }) => {
   state.changedFiles.forEach(file => {
@@ -43,14 +42,11 @@ export const createTempEntry = (
 ) =>
   new Promise(resolve => {
     const worker = new FilesDecoratorWorker();
-    const fullName =
-      name.slice(-1) !== '/' && type === 'tree' ? `${name}/` : name;
+    const fullName = name.slice(-1) !== '/' && type === 'tree' ? `${name}/` : name;
 
     if (state.entries[name]) {
       flash(
-        `The name "${name
-          .split('/')
-          .pop()}" is already taken in this directory.`,
+        `The name "${name.split('/').pop()}" is already taken in this directory.`,
         'alert',
         document,
         null,
@@ -119,3 +115,4 @@ export const updateDelayViewerUpdated = ({ commit }, delay) => {
 export * from './actions/tree';
 export * from './actions/file';
 export * from './actions/project';
+export * from './actions/merge_request';
diff --git a/app/assets/javascripts/ide/stores/actions/file.js b/app/assets/javascripts/ide/stores/actions/file.js
index ddc4b757bf9..c21c1a3f5d4 100644
--- a/app/assets/javascripts/ide/stores/actions/file.js
+++ b/app/assets/javascripts/ide/stores/actions/file.js
@@ -46,53 +46,63 @@ export const setFileActive = ({ commit, state, getters, dispatch }, path) => {
   commit(types.SET_CURRENT_BRANCH, file.branchId);
 };
 
-export const getFileData = ({ state, commit, dispatch }, file) => {
+export const getFileData = ({ state, commit, dispatch }, { path, makeFileActive = true }) => {
+  const file = state.entries[path];
   commit(types.TOGGLE_LOADING, { entry: file });
-
   return service
     .getFileData(file.url)
     .then(res => {
       const pageTitle = decodeURI(normalizeHeaders(res.headers)['PAGE-TITLE']);
-
       setPageTitle(pageTitle);
 
       return res.json();
     })
     .then(data => {
       commit(types.SET_FILE_DATA, { data, file });
-      commit(types.TOGGLE_FILE_OPEN, file.path);
-      dispatch('setFileActive', file.path);
+      commit(types.TOGGLE_FILE_OPEN, path);
+      if (makeFileActive) dispatch('setFileActive', path);
       commit(types.TOGGLE_LOADING, { entry: file });
     })
     .catch(() => {
       commit(types.TOGGLE_LOADING, { entry: file });
-      flash(
-        'Error loading file data. Please try again.',
-        'alert',
-        document,
-        null,
-        false,
-        true,
-      );
+      flash('Error loading file data. Please try again.', 'alert', document, null, false, true);
     });
 };
 
-export const getRawFileData = ({ commit, dispatch }, file) =>
-  service
-    .getRawFileData(file)
-    .then(raw => {
-      commit(types.SET_FILE_RAW_DATA, { file, raw });
-    })
-    .catch(() =>
-      flash(
-        'Error loading file content. Please try again.',
-        'alert',
-        document,
-        null,
-        false,
-        true,
-      ),
-    );
+export const setFileMrChange = ({ state, commit }, { file, mrChange }) => {
+  commit(types.SET_FILE_MERGE_REQUEST_CHANGE, { file, mrChange });
+};
+
+export const getRawFileData = ({ state, commit, dispatch }, { path, baseSha }) => {
+  const file = state.entries[path];
+  return new Promise((resolve, reject) => {
+    service
+      .getRawFileData(file)
+      .then(raw => {
+        commit(types.SET_FILE_RAW_DATA, { file, raw });
+        if (file.mrChange && file.mrChange.new_file === false) {
+          service
+            .getBaseRawFileData(file, baseSha)
+            .then(baseRaw => {
+              commit(types.SET_FILE_BASE_RAW_DATA, {
+                file,
+                baseRaw,
+              });
+              resolve(raw);
+            })
+            .catch(e => {
+              reject(e);
+            });
+        } else {
+          resolve(raw);
+        }
+      })
+      .catch(() => {
+        flash('Error loading file content. Please try again.');
+        reject();
+      });
+  });
+};
 
 export const changeFileContent = ({ state, commit }, { path, content }) => {
   const file = state.entries[path];
@@ -119,10 +129,7 @@ export const setFileEOL = ({ getters, commit }, { eol }) => {
   }
 };
 
-export const setEditorPosition = (
-  { getters, commit },
-  { editorRow, editorColumn },
-) => {
+export const setEditorPosition = ({ getters, commit }, { editorRow, editorColumn }) => {
   if (getters.activeFile) {
     commit(types.SET_FILE_POSITION, {
       file: getters.activeFile,
diff --git a/app/assets/javascripts/ide/stores/actions/merge_request.js b/app/assets/javascripts/ide/stores/actions/merge_request.js
new file mode 100644
index 00000000000..da73034fd7d
--- /dev/null
+++ b/app/assets/javascripts/ide/stores/actions/merge_request.js
@@ -0,0 +1,84 @@
+import flash from '~/flash';
+import service from '../../services';
+import * as types from '../mutation_types';
+
+export const getMergeRequestData = (
+  { commit, state, dispatch },
+  { projectId, mergeRequestId, force = false } = {},
+) =>
+  new Promise((resolve, reject) => {
+    if (!state.projects[projectId].mergeRequests[mergeRequestId] || force) {
+      service
+        .getProjectMergeRequestData(projectId, mergeRequestId)
+        .then(res => res.data)
+        .then(data => {
+          commit(types.SET_MERGE_REQUEST, {
+            projectPath: projectId,
+            mergeRequestId,
+            mergeRequest: data,
+          });
+          if (!state.currentMergeRequestId) {
+            commit(types.SET_CURRENT_MERGE_REQUEST, mergeRequestId);
+          }
+          resolve(data);
+        })
+        .catch(() => {
+          flash('Error loading merge request data. Please try again.');
+          reject(new Error(`Merge Request not loaded ${projectId}`));
+        });
+    } else {
+      resolve(state.projects[projectId].mergeRequests[mergeRequestId]);
+    }
+  });
+
+export const getMergeRequestChanges = (
+  { commit, state, dispatch },
+  { projectId, mergeRequestId, force = false } = {},
+) =>
+  new Promise((resolve, reject) => {
+    if (!state.projects[projectId].mergeRequests[mergeRequestId].changes.length || force) {
+      service
+        .getProjectMergeRequestChanges(projectId, mergeRequestId)
+        .then(res => res.data)
+        .then(data => {
+          commit(types.SET_MERGE_REQUEST_CHANGES, {
+            projectPath: projectId,
+            mergeRequestId,
+            changes: data,
+          });
+          resolve(data);
+        })
+        .catch(() => {
+          flash('Error loading merge request changes. Please try again.');
+          reject(new Error(`Merge Request Changes not loaded ${projectId}`));
+        });
+    } else {
+      resolve(state.projects[projectId].mergeRequests[mergeRequestId].changes);
+    }
+  });
+
+export const getMergeRequestVersions = (
+  { commit, state, dispatch },
+  { projectId, mergeRequestId, force = false } = {},
+) =>
+  new Promise((resolve, reject) => {
+    if (!state.projects[projectId].mergeRequests[mergeRequestId].versions.length || force) {
+      service
+        .getProjectMergeRequestVersions(projectId, mergeRequestId)
+        .then(res => res.data)
+        .then(data => {
+          commit(types.SET_MERGE_REQUEST_VERSIONS, {
+            projectPath: projectId,
+            mergeRequestId,
+            versions: data,
+          });
+          resolve(data);
+        })
+        .catch(() => {
+          flash('Error loading merge request versions. Please try again.');
+          reject(new Error(`Merge Request Versions not loaded ${projectId}`));
+        });
+    } else {
+      resolve(state.projects[projectId].mergeRequests[mergeRequestId].versions);
+    }
+  });
diff --git a/app/assets/javascripts/ide/stores/actions/tree.js b/app/assets/javascripts/ide/stores/actions/tree.js
index 70a969a0325..6536be04f0a 100644
--- a/app/assets/javascripts/ide/stores/actions/tree.js
+++ b/app/assets/javascripts/ide/stores/actions/tree.js
@@ -2,9 +2,7 @@ import { normalizeHeaders } from '~/lib/utils/common_utils';
 import flash from '~/flash';
 import service from '../../services';
 import * as types from '../mutation_types';
-import {
-  findEntry,
-} from '../utils';
+import { findEntry } from '../utils';
 import FilesDecoratorWorker from '../workers/files_decorator_worker';
 
 export const toggleTreeOpen = ({ commit, dispatch }, path) => {
@@ -21,23 +19,24 @@ export const handleTreeEntryAction = ({ commit, dispatch }, row) => {
 
     dispatch('setFileActive', row.path);
   } else {
-    dispatch('getFileData', row);
+    dispatch('getFileData', { path: row.path });
   }
 };
 
 export const getLastCommitData = ({ state, commit, dispatch, getters }, tree = state) => {
   if (!tree || tree.lastCommitPath === null || !tree.lastCommitPath) return;
 
-  service.getTreeLastCommit(tree.lastCommitPath)
-    .then((res) => {
+  service
+    .getTreeLastCommit(tree.lastCommitPath)
+    .then(res => {
       const lastCommitPath = normalizeHeaders(res.headers)['MORE-LOGS-URL'] || null;
 
       commit(types.SET_LAST_COMMIT_URL, { tree, url: lastCommitPath });
 
       return res.json();
     })
-    .then((data) => {
-      data.forEach((lastCommit) => {
+    .then(data => {
+      data.forEach(lastCommit => {
         const entry = findEntry(tree.tree, lastCommit.type, lastCommit.file_name);
 
         if (entry) {
@@ -50,44 +49,47 @@ export const getLastCommitData = ({ state, commit, dispatch, getters }, tree = s
     .catch(() => flash('Error fetching log data.', 'alert', document, null, false, true));
 };
 
-export const getFiles = (
-  { state, commit, dispatch },
-  { projectId, branchId } = {},
-) => new Promise((resolve, reject) => {
-  if (!state.trees[`${projectId}/${branchId}`]) {
-    const selectedProject = state.projects[projectId];
-    commit(types.CREATE_TREE, { treePath: `${projectId}/${branchId}` });
-
-    service
-      .getFiles(selectedProject.web_url, branchId)
-      .then(res => res.json())
-      .then((data) => {
-        const worker = new FilesDecoratorWorker();
-        worker.addEventListener('message', (e) => {
-          const { entries, treeList } = e.data;
-          const selectedTree = state.trees[`${projectId}/${branchId}`];
-
-          commit(types.SET_ENTRIES, entries);
-          commit(types.SET_DIRECTORY_DATA, { treePath: `${projectId}/${branchId}`, data: treeList });
-          commit(types.TOGGLE_LOADING, { entry: selectedTree, forceValue: false });
-
-          worker.terminate();
-
-          resolve();
-        });
-
-        worker.postMessage({
-          data,
-          projectId,
-          branchId,
+export const getFiles = ({ state, commit, dispatch }, { projectId, branchId } = {}) =>
+  new Promise((resolve, reject) => {
+    if (!state.trees[`${projectId}/${branchId}`]) {
+      const selectedProject = state.projects[projectId];
+      commit(types.CREATE_TREE, { treePath: `${projectId}/${branchId}` });
+
+      service
+        .getFiles(selectedProject.web_url, branchId)
+        .then(res => res.json())
+        .then(data => {
+          const worker = new FilesDecoratorWorker();
+          worker.addEventListener('message', e => {
+            const { entries, treeList } = e.data;
+            const selectedTree = state.trees[`${projectId}/${branchId}`];
+
+            commit(types.SET_ENTRIES, entries);
+            commit(types.SET_DIRECTORY_DATA, {
+              treePath: `${projectId}/${branchId}`,
+              data: treeList,
+            });
+            commit(types.TOGGLE_LOADING, {
+              entry: selectedTree,
+              forceValue: false,
+            });
+
+            worker.terminate();
+
+            resolve();
+          });
+
+          worker.postMessage({
+            data,
+            projectId,
+            branchId,
+          });
+        })
+        .catch(e => {
+          flash('Error loading tree data. Please try again.', 'alert', document, null, false, true);
+          reject(e);
         });
-      })
-      .catch((e) => {
-        flash('Error loading tree data. Please try again.', 'alert', document, null, false, true);
-        reject(e);
-      });
-  } else {
-    resolve();
-  }
-});
-
+    } else {
+      resolve();
+    }
+  });
diff --git a/app/assets/javascripts/ide/stores/getters.js b/app/assets/javascripts/ide/stores/getters.js
index eba325a31df..a77cdbc13c8 100644
--- a/app/assets/javascripts/ide/stores/getters.js
+++ b/app/assets/javascripts/ide/stores/getters.js
@@ -1,10 +1,8 @@
-export const activeFile = state =>
-  state.openFiles.find(file => file.active) || null;
+export const activeFile = state => state.openFiles.find(file => file.active) || null;
 
 export const addedFiles = state => state.changedFiles.filter(f => f.tempFile);
 
-export const modifiedFiles = state =>
-  state.changedFiles.filter(f => !f.tempFile);
+export const modifiedFiles = state => state.changedFiles.filter(f => !f.tempFile);
 
 export const projectsWithTrees = state =>
   Object.keys(state.projects).map(projectId => {
@@ -23,8 +21,17 @@ export const projectsWithTrees = state =>
     };
   });
 
+export const currentMergeRequest = state => {
+  if (state.projects[state.currentProjectId]) {
+    return state.projects[state.currentProjectId].mergeRequests[state.currentMergeRequestId];
+  }
+  return null;
+};
+
 // eslint-disable-next-line no-confusing-arrow
 export const currentIcon = state =>
   state.rightPanelCollapsed ? 'angle-double-left' : 'angle-double-right';
 
 export const hasChanges = state => !!state.changedFiles.length;
+
+export const hasMergeRequest = state => !!state.currentMergeRequestId;
diff --git a/app/assets/javascripts/ide/stores/mutation_types.js b/app/assets/javascripts/ide/stores/mutation_types.js
index e28f190897c..e06be0a3fe9 100644
--- a/app/assets/javascripts/ide/stores/mutation_types.js
+++ b/app/assets/javascripts/ide/stores/mutation_types.js
@@ -11,6 +11,12 @@ export const SET_PROJECT = 'SET_PROJECT';
 export const SET_CURRENT_PROJECT = 'SET_CURRENT_PROJECT';
 export const TOGGLE_PROJECT_OPEN = 'TOGGLE_PROJECT_OPEN';
 
+// Merge Request Mutation Types
+export const SET_MERGE_REQUEST = 'SET_MERGE_REQUEST';
+export const SET_CURRENT_MERGE_REQUEST = 'SET_CURRENT_MERGE_REQUEST';
+export const SET_MERGE_REQUEST_CHANGES = 'SET_MERGE_REQUEST_CHANGES';
+export const SET_MERGE_REQUEST_VERSIONS = 'SET_MERGE_REQUEST_VERSIONS';
+
 // Branch Mutation Types
 export const SET_BRANCH = 'SET_BRANCH';
 export const SET_BRANCH_WORKING_REFERENCE = 'SET_BRANCH_WORKING_REFERENCE';
@@ -28,6 +34,7 @@ export const SET_FILE_DATA = 'SET_FILE_DATA';
 export const TOGGLE_FILE_OPEN = 'TOGGLE_FILE_OPEN';
 export const SET_FILE_ACTIVE = 'SET_FILE_ACTIVE';
 export const SET_FILE_RAW_DATA = 'SET_FILE_RAW_DATA';
+export const SET_FILE_BASE_RAW_DATA = 'SET_FILE_BASE_RAW_DATA';
 export const UPDATE_FILE_CONTENT = 'UPDATE_FILE_CONTENT';
 export const SET_FILE_LANGUAGE = 'SET_FILE_LANGUAGE';
 export const SET_FILE_POSITION = 'SET_FILE_POSITION';
@@ -39,5 +46,6 @@ export const TOGGLE_FILE_CHANGED = 'TOGGLE_FILE_CHANGED';
 export const SET_CURRENT_BRANCH = 'SET_CURRENT_BRANCH';
 export const SET_ENTRIES = 'SET_ENTRIES';
 export const CREATE_TMP_ENTRY = 'CREATE_TMP_ENTRY';
+export const SET_FILE_MERGE_REQUEST_CHANGE = 'SET_FILE_MERGE_REQUEST_CHANGE';
 export const UPDATE_VIEWER = 'UPDATE_VIEWER';
 export const UPDATE_DELAY_VIEWER_CHANGE = 'UPDATE_DELAY_VIEWER_CHANGE';
diff --git a/app/assets/javascripts/ide/stores/mutations.js b/app/assets/javascripts/ide/stores/mutations.js
index da41fc9285c..5e5eb831662 100644
--- a/app/assets/javascripts/ide/stores/mutations.js
+++ b/app/assets/javascripts/ide/stores/mutations.js
@@ -1,5 +1,6 @@
 import * as types from './mutation_types';
 import projectMutations from './mutations/project';
+import mergeRequestMutation from './mutations/merge_request';
 import fileMutations from './mutations/file';
 import treeMutations from './mutations/tree';
 import branchMutations from './mutations/branch';
@@ -11,10 +12,7 @@ export default {
   [types.TOGGLE_LOADING](state, { entry, forceValue = undefined }) {
     if (entry.path) {
       Object.assign(state.entries[entry.path], {
-        loading:
-          forceValue !== undefined
-            ? forceValue
-            : !state.entries[entry.path].loading,
+        loading: forceValue !== undefined ? forceValue : !state.entries[entry.path].loading,
       });
     } else {
       Object.assign(entry, {
@@ -83,9 +81,7 @@ export default {
 
     if (!foundEntry) {
       Object.assign(state.trees[`${projectId}/${branchId}`], {
-        tree: state.trees[`${projectId}/${branchId}`].tree.concat(
-          data.treeList,
-        ),
+        tree: state.trees[`${projectId}/${branchId}`].tree.concat(data.treeList),
       });
     }
   },
@@ -100,6 +96,7 @@ export default {
     });
   },
   ...projectMutations,
+  ...mergeRequestMutation,
   ...fileMutations,
   ...treeMutations,
   ...branchMutations,
diff --git a/app/assets/javascripts/ide/stores/mutations/file.js b/app/assets/javascripts/ide/stores/mutations/file.js
index 2500f13db7c..692fe39b38e 100644
--- a/app/assets/javascripts/ide/stores/mutations/file.js
+++ b/app/assets/javascripts/ide/stores/mutations/file.js
@@ -28,6 +28,8 @@ export default {
       rawPath: data.raw_path,
       binary: data.binary,
       renderError: data.render_error,
+      raw: null,
+      baseRaw: null,
     });
   },
   [types.SET_FILE_RAW_DATA](state, { file, raw }) {
@@ -35,6 +37,11 @@ export default {
       raw,
     });
   },
+  [types.SET_FILE_BASE_RAW_DATA](state, { file, baseRaw }) {
+    Object.assign(state.entries[file.path], {
+      baseRaw,
+    });
+  },
   [types.UPDATE_FILE_CONTENT](state, { path, content }) {
     const changed = content !== state.entries[path].raw;
 
@@ -59,6 +66,11 @@ export default {
       editorColumn,
     });
   },
+  [types.SET_FILE_MERGE_REQUEST_CHANGE](state, { file, mrChange }) {
+    Object.assign(state.entries[file.path], {
+      mrChange,
+    });
+  },
   [types.DISCARD_FILE_CHANGES](state, path) {
     Object.assign(state.entries[path], {
       content: state.entries[path].raw,
diff --git a/app/assets/javascripts/ide/stores/mutations/merge_request.js b/app/assets/javascripts/ide/stores/mutations/merge_request.js
new file mode 100644
index 00000000000..334819fe702
--- /dev/null
+++ b/app/assets/javascripts/ide/stores/mutations/merge_request.js
@@ -0,0 +1,33 @@
+import * as types from '../mutation_types';
+
+export default {
+  [types.SET_CURRENT_MERGE_REQUEST](state, currentMergeRequestId) {
+    Object.assign(state, {
+      currentMergeRequestId,
+    });
+  },
+  [types.SET_MERGE_REQUEST](state, { projectPath, mergeRequestId, mergeRequest }) {
+    Object.assign(state.projects[projectPath], {
+      mergeRequests: {
+        [mergeRequestId]: {
+          ...mergeRequest,
+          active: true,
+          changes: [],
+          versions: [],
+          baseCommitSha: null,
+        },
+      },
+    });
+  },
+  [types.SET_MERGE_REQUEST_CHANGES](state, { projectPath, mergeRequestId, changes }) {
+    Object.assign(state.projects[projectPath].mergeRequests[mergeRequestId], {
+      changes,
+    });
+  },
+  [types.SET_MERGE_REQUEST_VERSIONS](state, { projectPath, mergeRequestId, versions }) {
+    Object.assign(state.projects[projectPath].mergeRequests[mergeRequestId], {
+      versions,
+      baseCommitSha: versions.length ? versions[0].base_commit_sha : null,
+    });
+  },
+};
diff --git a/app/assets/javascripts/ide/stores/mutations/project.js b/app/assets/javascripts/ide/stores/mutations/project.js
index 2816562a919..284b39a2c72 100644
--- a/app/assets/javascripts/ide/stores/mutations/project.js
+++ b/app/assets/javascripts/ide/stores/mutations/project.js
@@ -11,6 +11,7 @@ export default {
     Object.assign(project, {
       tree: [],
       branches: {},
+      mergeRequests: {},
       active: true,
     });
 
diff --git a/app/assets/javascripts/ide/stores/state.js b/app/assets/javascripts/ide/stores/state.js
index 6110f54951c..e5cc8814000 100644
--- a/app/assets/javascripts/ide/stores/state.js
+++ b/app/assets/javascripts/ide/stores/state.js
@@ -1,6 +1,7 @@
 export default () => ({
   currentProjectId: '',
   currentBranchId: '',
+  currentMergeRequestId: '',
   changedFiles: [],
   endpoints: {},
   lastCommitMsg: '',
diff --git a/app/assets/javascripts/ide/stores/utils.js b/app/assets/javascripts/ide/stores/utils.js
index 487ea1ead8e..3389eeeaa2e 100644
--- a/app/assets/javascripts/ide/stores/utils.js
+++ b/app/assets/javascripts/ide/stores/utils.js
@@ -38,7 +38,7 @@ export const dataStructure = () => ({
   eol: '',
 });
 
-export const decorateData = (entity) => {
+export const decorateData = entity => {
   const {
     id,
     projectId,
@@ -57,7 +57,6 @@ export const decorateData = (entity) => {
     base64 = false,
 
     file_lock,
-
   } = entity;
 
   return {
@@ -80,17 +79,15 @@ export const decorateData = (entity) => {
     base64,
 
     file_lock,
-
   };
 };
 
-export const findEntry = (tree, type, name, prop = 'name') => tree.find(
-  f => f.type === type && f[prop] === name,
-);
+export const findEntry = (tree, type, name, prop = 'name') =>
+  tree.find(f => f.type === type && f[prop] === name);
 
 export const findIndexOfFile = (state, file) => state.findIndex(f => f.path === file.path);
 
-export const setPageTitle = (title) => {
+export const setPageTitle = title => {
   document.title = title;
 };
 
@@ -120,6 +117,11 @@ const sortTreesByTypeAndName = (a, b) => {
   return 0;
 };
 
-export const sortTree = sortedTree => sortedTree.map(entity => Object.assign(entity, {
-  tree: entity.tree.length ? sortTree(entity.tree) : [],
-})).sort(sortTreesByTypeAndName);
+export const sortTree = sortedTree =>
+  sortedTree
+    .map(entity =>
+      Object.assign(entity, {
+        tree: entity.tree.length ? sortTree(entity.tree) : [],
+      }),
+    )
+    .sort(sortTreesByTypeAndName);
diff --git a/app/assets/javascripts/lib/utils/url_utility.js b/app/assets/javascripts/lib/utils/url_utility.js
index a266bb6771f..dd17544b656 100644
--- a/app/assets/javascripts/lib/utils/url_utility.js
+++ b/app/assets/javascripts/lib/utils/url_utility.js
@@ -51,7 +51,7 @@ export function removeParams(params) {
   const url = document.createElement('a');
   url.href = window.location.href;
 
-  params.forEach((param) => {
+  params.forEach(param => {
     url.search = removeParamQueryString(url.search, param);
   });
 
@@ -83,3 +83,11 @@ export function refreshCurrentPage() {
 export function redirectTo(url) {
   return window.location.assign(url);
 }
+
+export function webIDEUrl(route = undefined) {
+  let returnUrl = `${gon.relative_url_root}/-/ide/`;
+  if (route) {
+    returnUrl += `project${route}`;
+  }
+  return returnUrl;
+}
diff --git a/app/assets/javascripts/vue_merge_request_widget/components/mr_widget_header.vue b/app/assets/javascripts/vue_merge_request_widget/components/mr_widget_header.vue
index 3d886e7d628..18ee4c62bf1 100644
--- a/app/assets/javascripts/vue_merge_request_widget/components/mr_widget_header.vue
+++ b/app/assets/javascripts/vue_merge_request_widget/components/mr_widget_header.vue
@@ -1,53 +1,57 @@
 <script>
-  import tooltip from '~/vue_shared/directives/tooltip';
-  import { n__ } from '~/locale';
-  import icon from '~/vue_shared/components/icon.vue';
-  import clipboardButton from '~/vue_shared/components/clipboard_button.vue';
+import tooltip from '~/vue_shared/directives/tooltip';
+import { n__ } from '~/locale';
+import { webIDEUrl } from '~/lib/utils/url_utility';
+import icon from '~/vue_shared/components/icon.vue';
+import clipboardButton from '~/vue_shared/components/clipboard_button.vue';
 
-  export default {
-    name: 'MRWidgetHeader',
-    directives: {
-      tooltip,
+export default {
+  name: 'MRWidgetHeader',
+  directives: {
+    tooltip,
+  },
+  components: {
+    icon,
+    clipboardButton,
+  },
+  props: {
+    mr: {
+      type: Object,
+      required: true,
     },
-    components: {
-      icon,
-      clipboardButton,
+  },
+  computed: {
+    shouldShowCommitsBehindText() {
+      return this.mr.divergedCommitsCount > 0;
     },
-    props: {
-      mr: {
-        type: Object,
-        required: true,
-      },
+    commitsText() {
+      return n__('%d commit behind', '%d commits behind', this.mr.divergedCommitsCount);
     },
-    computed: {
-      shouldShowCommitsBehindText() {
-        return this.mr.divergedCommitsCount > 0;
-      },
-      commitsText() {
-        return n__('%d commit behind', '%d commits behind', this.mr.divergedCommitsCount);
-      },
-      branchNameClipboardData() {
-        // This supports code in app/assets/javascripts/copy_to_clipboard.js that
-        // works around ClipboardJS limitations to allow the context-specific
-        // copy/pasting of plain text or GFM.
-        return JSON.stringify({
-          text: this.mr.sourceBranch,
-          gfm: `\`${this.mr.sourceBranch}\``,
-        });
-      },
-      isSourceBranchLong() {
-        return this.isBranchTitleLong(this.mr.sourceBranch);
-      },
-      isTargetBranchLong() {
-        return this.isBranchTitleLong(this.mr.targetBranch);
-      },
+    branchNameClipboardData() {
+      // This supports code in app/assets/javascripts/copy_to_clipboard.js that
+      // works around ClipboardJS limitations to allow the context-specific
+      // copy/pasting of plain text or GFM.
+      return JSON.stringify({
+        text: this.mr.sourceBranch,
+        gfm: `\`${this.mr.sourceBranch}\``,
+      });
     },
-    methods: {
-      isBranchTitleLong(branchTitle) {
-        return branchTitle.length > 32;
-      },
+    isSourceBranchLong() {
+      return this.isBranchTitleLong(this.mr.sourceBranch);
     },
-  };
+    isTargetBranchLong() {
+      return this.isBranchTitleLong(this.mr.targetBranch);
+    },
+    webIdePath() {
+      return webIDEUrl(this.mr.statusPath.replace('.json', ''));
+    },
+  },
+  methods: {
+    isBranchTitleLong(branchTitle) {
+      return branchTitle.length > 32;
+    },
+  },
+};
 </script>
 <template>
   <div class="mr-source-target">
@@ -96,6 +100,13 @@
     </div>
 
     <div v-if="mr.isOpen">
+      <a
+        v-if="!mr.sourceBranchRemoved"
+        :href="webIdePath"
+        class="btn btn-sm btn-default inline js-web-ide"
+      >
+        {{ s__("mrWidget|Web IDE") }}
+      </a>
       <button
         data-target="#modal_merge_info"
         data-toggle="modal"
diff --git a/app/assets/stylesheets/pages/repo.scss b/app/assets/stylesheets/pages/repo.scss
index 34340853165..96e781146a7 100644
--- a/app/assets/stylesheets/pages/repo.scss
+++ b/app/assets/stylesheets/pages/repo.scss
@@ -53,6 +53,7 @@
       flex: 1;
       white-space: nowrap;
       text-overflow: ellipsis;
+      max-width: inherit;
 
       svg {
         vertical-align: middle;