Basic Setup for MR Showing

23 files changed, 1006 insertions, 314 deletions

diff --git a/app/assets/javascripts/api.js b/app/assets/javascripts/api.js
index cbcefb2c18f..bed20b36868 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',
   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 +92,28 @@ 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);
+  },
+
+  // Return Merge Request Changes
+  mergeRequestChanges(projectPath, mergeRequestId) {
+    const url = Api.buildUrl(Api.mergeRequestChangesPath)
+      .replace(':id', encodeURIComponent(projectPath))
+      .replace(':mrid', mergeRequestId);
 
     return axios.get(url);
   },
@@ -99,33 +126,39 @@ const Api = {
         .replace(':namespace_path', namespacePath)
         .replace(':project_path', projectPath);
     } else {
-      url = Api.buildUrl(Api.groupLabelsPath).replace(':namespace_path', namespacePath);
+      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 +169,34 @@ 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 +205,8 @@ 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 +214,13 @@ 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/editor_mode_dropdown.vue b/app/assets/javascripts/ide/components/editor_mode_dropdown.vue
index 170347881e0..42b00b5d9df 100644
--- a/app/assets/javascripts/ide/components/editor_mode_dropdown.vue
+++ b/app/assets/javascripts/ide/components/editor_mode_dropdown.vue
@@ -1,31 +1,36 @@
 <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: {
+    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,
-      },
+    hasMergeRequest: {
+      type: Boolean,
+      required: false,
+      default: false,
     },
-    methods: {
-      changeMode(mode) {
-        this.$emit('click', mode);
-      },
+    viewer: {
+      type: String,
+      required: true,
     },
-  };
+    showShadow: {
+      type: Boolean,
+      required: true,
+    },
+  },
+  methods: {
+    changeMode(mode) {
+      this.$emit('click', mode);
+    },
+  },
+};
 </script>
 
 <template>
@@ -43,7 +48,10 @@
       }"
       data-toggle="dropdown"
     >
-      <template v-if="viewer === 'editor'">
+      <template v-if="viewer === 'mrdiff'">
+        {{ __('Reviewing (merge request)') }}
+      </template>
+      <template v-else-if="viewer === 'editor'">
         {{ __('Editing') }}
       </template>
       <template v-else>
@@ -57,6 +65,21 @@
     </button>
     <div class="dropdown-menu dropdown-menu-selectable dropdown-open-left">
       <ul>
+        <li v-if="hasMergeRequest">
+          <a
+            href="#"
+            @click.prevent="changeMode('mrdiff')"
+            :class="{
+              'is-active': viewer === 'mrdiff',
+            }"
+          >
+            <strong class="dropdown-menu-inner-title">{{ __('Reviewing (merge request)') }}</strong>
+            <span class="dropdown-menu-inner-content">
+              {{ __('Compare changes of the merge request') }}
+            </span>
+          </a>
+        </li>
+        <li v-if="hasMergeRequest" role="separator" class="divider"></li>
         <li>
           <a
             href="#"
diff --git a/app/assets/javascripts/ide/components/ide.vue b/app/assets/javascripts/ide/components/ide.vue
index 015e750525a..f300afa24ac 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']),
+    ...mapGetters(['activeFile', 'hasChanges', 'hasMergeRequest']),
+  },
+  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"
+          :has-merge-request="hasMergeRequest"
         />
         <repo-editor
           class="multi-file-edit-pane-content"
diff --git a/app/assets/javascripts/ide/components/repo_editor.vue b/app/assets/javascripts/ide/components/repo_editor.vue
index e73d1ce839f..d647d3b87fb 100644
--- a/app/assets/javascripts/ide/components/repo_editor.vue
+++ b/app/assets/javascripts/ide/components/repo_editor.vue
@@ -70,7 +70,9 @@ export default {
 
       this.getRawFileData(this.file)
         .then(() => {
-          const viewerPromise = this.delayViewerUpdated ? this.updateViewer('editor') : Promise.resolve();
+          const viewerPromise = this.delayViewerUpdated
+            ? this.updateViewer('editor')
+            : Promise.resolve();
 
           return viewerPromise;
         })
@@ -78,8 +80,15 @@ export default {
           this.updateDelayViewerUpdated(false);
           this.createEditorInstance();
         })
-        .catch((err) => {
-          flash('Error setting up monaco. Please try again.', 'alert', document, null, false, true);
+        .catch(err => {
+          flash(
+            'Error setting up monaco. Please try again.',
+            'alert',
+            document,
+            null,
+            false,
+            true,
+          );
           throw err;
         });
     },
@@ -101,9 +110,13 @@ 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_tabs.vue b/app/assets/javascripts/ide/components/repo_tabs.vue
index 8ea64ddf84a..37e90d3ba7e 100644
--- a/app/assets/javascripts/ide/components/repo_tabs.vue
+++ b/app/assets/javascripts/ide/components/repo_tabs.vue
@@ -1,42 +1,47 @@
 <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.$refs.tabsScroller.offsetWidth;
-    },
-    methods: {
-      ...mapActions(['updateViewer']),
+    hasMergeRequest: {
+      type: Boolean,
+      required: true,
+      default: false,
     },
-  };
+  },
+  data() {
+    return {
+      showShadow: false,
+    };
+  },
+  updated() {
+    if (!this.$refs.tabsScroller) return;
+
+    this.showShadow =
+      this.$refs.tabsScroller.scrollWidth > this.$refs.tabsScroller.offsetWidth;
+  },
+  methods: {
+    ...mapActions(['updateViewer']),
+  },
+};
 </script>
 
 <template>
@@ -55,6 +60,7 @@
       :viewer="viewer"
       :show-shadow="showShadow"
       :has-changes="hasChanges"
+      :has-merge-request="hasMergeRequest"
       @click="updateViewer"
     />
   </div>
diff --git a/app/assets/javascripts/ide/ide_router.js b/app/assets/javascripts/ide/ide_router.js
index db89c1d44db..f054a0a0364 100644
--- a/app/assets/javascripts/ide/ide_router.js
+++ b/app/assets/javascripts/ide/ide_router.js
@@ -2,6 +2,7 @@ import Vue from 'vue';
 import VueRouter from 'vue-router';
 import flash from '~/flash';
 import store from './stores';
+import { getTreeEntry } from './stores/utils';
 
 Vue.use(VueRouter);
 
@@ -44,7 +45,7 @@ const router = new VueRouter({
           component: EmptyRouterComponent,
         },
         {
-          path: 'mr/:mrid',
+          path: 'merge_requests/:mrid',
           component: EmptyRouterComponent,
         },
       ],
@@ -96,6 +97,84 @@ 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,
+              });
+
+              store
+                .dispatch('getFiles', {
+                  projectId: fullProjectId,
+                  branchId: mr.source_branch,
+                })
+                .then(() => {
+                  store
+                    .dispatch('getMergeRequestChanges', {
+                      projectId: fullProjectId,
+                      mergeRequestId: to.params.mrid,
+                    })
+                    .then(mrChanges => {
+                      if (mrChanges.changes.length > 0) {
+                      }
+                      mrChanges.changes.forEach((change, ind) => {
+                        console.log(`CHANGE : ${ind} : `, change);
+
+                        const changeTreeEntry =
+                          store.state.entries[change.new_path];
+
+                        console.log(
+                          'Tree Entry for the change ',
+                          changeTreeEntry,
+                          change.diff,
+                        );
+
+                        if (changeTreeEntry) {
+                          store.dispatch('setFileMrDiff', {
+                            file: changeTreeEntry,
+                            mrDiff: change.diff,
+                          });
+                          store.dispatch('setFileTargetBranch', {
+                            file: changeTreeEntry,
+                            targetBranch: mrChanges.target_branch,
+                          });
+
+                          if (ind === 0) {
+                            store.dispatch('getFileData', change.new_path);
+                          } else {
+                            // TODO : Implement Tab reloading
+                            store.dispatch('preloadFileTab', changeTreeEntry);
+                          }
+                        } else {
+                          console.warn(`No Tree Entry for ${change.new_path}`);
+                        }
+                      });
+                    })
+                    .catch(e => {
+                      flash(
+                        'Error while loading the merge request changes. Please try again.',
+                      );
+                      throw e;
+                    });
+                })
+                .catch(e => {
+                  flash(
+                    'Error while loading the branch files. Please try again.',
+                  );
+                  throw e;
+                });
+            })
+            .catch(e => {
+              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..8e16df99a03 100644
--- a/app/assets/javascripts/ide/lib/common/model.js
+++ b/app/assets/javascripts/ide/lib/common/model.js
@@ -22,6 +22,16 @@ export default class Model {
       )),
     );
 
+    if (this.file.targetBranch) {
+      this.disposable.add(
+        (this.targetModel = this.monaco.editor.createModel(
+          this.file.targetRaw,
+          undefined,
+          new this.monaco.Uri(null, null, `target/${this.file.path}`),
+        )),
+      );
+    }
+
     this.events = new Map();
 
     this.updateContent = this.updateContent.bind(this);
@@ -58,6 +68,10 @@ export default class Model {
     return this.originalModel;
   }
 
+  getTargetModel() {
+    return this.targetModel;
+  }
+
   setValue(value) {
     this.getModel().setValue(value);
   }
diff --git a/app/assets/javascripts/ide/lib/diff/revert_patch.js b/app/assets/javascripts/ide/lib/diff/revert_patch.js
new file mode 100644
index 00000000000..21c90adedd8
--- /dev/null
+++ b/app/assets/javascripts/ide/lib/diff/revert_patch.js
@@ -0,0 +1,183 @@
+export function revertPatch(source, uniDiff, options = {}) {
+  if (typeof uniDiff === 'string') {
+    uniDiff = parsePatch(uniDiff);
+  }
+
+  if (Array.isArray(uniDiff)) {
+    if (uniDiff.length > 1) {
+      throw new Error('applyPatch only works with a single input.');
+    }
+
+    uniDiff = uniDiff[0];
+  }
+
+  // Apply the diff to the input
+  let lines = source.split(/\r\n|[\n\v\f\r\x85]/),
+    delimiters = source.match(/\r\n|[\n\v\f\r\x85]/g) || [],
+    hunks = uniDiff.hunks,
+    compareLine =
+      options.compareLine ||
+      ((lineNumber, line, operation, patchContent) => line === patchContent),
+    errorCount = 0,
+    fuzzFactor = options.fuzzFactor || 0,
+    minLine = 0,
+    offset = 0,
+    removeEOFNL,
+    addEOFNL;
+
+  /**
+   * Checks if the hunk exactly fits on the provided location
+   */
+  function hunkFits(hunk, toPos) {
+    for (let j = 0; j < hunk.lines.length; j++) {
+      let line = hunk.lines[j],
+        operation = line[0],
+        content = line.substr(1);
+
+      if (operation === ' ' || operation === '-') {
+        // Context sanity check
+        if (!compareLine(toPos + 1, lines[toPos], operation, content)) {
+          errorCount++;
+
+          if (errorCount > fuzzFactor) {
+            return false;
+          }
+        }
+        toPos++;
+      }
+    }
+
+    return true;
+  }
+
+  // Search best fit offsets for each hunk based on the previous ones
+  for (let i = 0; i < hunks.length; i++) {
+    let hunk = hunks[i],
+      maxLine = lines.length - hunk.oldLines,
+      localOffset = 0,
+      toPos = offset + hunk.oldStart - 1;
+
+    const iterator = distanceIterator(toPos, minLine, maxLine);
+
+    for (; localOffset !== undefined; localOffset = iterator()) {
+      if (hunkFits(hunk, toPos + localOffset)) {
+        hunk.offset = offset += localOffset;
+        break;
+      }
+    }
+
+    if (localOffset === undefined) {
+      return false;
+    }
+
+    // Set lower text limit to end of the current hunk, so next ones don't try
+    // to fit over already patched text
+    minLine = hunk.offset + hunk.oldStart + hunk.oldLines;
+  }
+
+  // Apply patch hunks
+  let diffOffset = 0;
+  for (let i = 0; i < hunks.length; i++) {
+    let hunk = hunks[i],
+      toPos = hunk.oldStart + hunk.offset + diffOffset - 1;
+    diffOffset += hunk.newLines - hunk.oldLines;
+
+    if (toPos < 0) {
+      // Creating a new file
+      toPos = 0;
+    }
+
+    for (let j = 0; j < hunk.lines.length; j++) {
+      let line = hunk.lines[j],
+        operation = line[0],
+        content = line.substr(1),
+        delimiter = hunk.linedelimiters[j];
+
+      // Turned around the commands to revert the applying
+      if (operation === ' ') {
+        toPos++;
+      } else if (operation === '+') {
+        lines.splice(toPos, 1);
+        delimiters.splice(toPos, 1);
+        /* istanbul ignore else */
+      } else if (operation === '-') {
+        lines.splice(toPos, 0, content);
+        delimiters.splice(toPos, 0, delimiter);
+        toPos++;
+      } else if (operation === '\\') {
+        const previousOperation = hunk.lines[j - 1]
+          ? hunk.lines[j - 1][0]
+          : null;
+        if (previousOperation === '+') {
+          removeEOFNL = true;
+        } else if (previousOperation === '-') {
+          addEOFNL = true;
+        }
+      }
+    }
+  }
+
+  // Handle EOFNL insertion/removal
+  if (removeEOFNL) {
+    while (!lines[lines.length - 1]) {
+      lines.pop();
+      delimiters.pop();
+    }
+  } else if (addEOFNL) {
+    lines.push('');
+    delimiters.push('\n');
+  }
+  for (let _k = 0; _k < lines.length - 1; _k++) {
+    lines[_k] = lines[_k] + delimiters[_k];
+  }
+  return lines.join('');
+}
+
+/**
+ * Utility Function
+ * @param {*} start
+ * @param {*} minLine
+ * @param {*} maxLine
+ */
+const distanceIterator = function(start, minLine, maxLine) {
+  let wantForward = true,
+    backwardExhausted = false,
+    forwardExhausted = false,
+    localOffset = 1;
+
+  return function iterator() {
+    if (wantForward && !forwardExhausted) {
+      if (backwardExhausted) {
+        localOffset++;
+      } else {
+        wantForward = false;
+      }
+
+      // Check if trying to fit beyond text length, and if not, check it fits
+      // after offset location (or desired location on first iteration)
+      if (start + localOffset <= maxLine) {
+        return localOffset;
+      }
+
+      forwardExhausted = true;
+    }
+
+    if (!backwardExhausted) {
+      if (!forwardExhausted) {
+        wantForward = true;
+      }
+
+      // Check if trying to fit before text beginning, and if not, check it fits
+      // before offset location
+      if (minLine <= start - localOffset) {
+        return -localOffset++;
+      }
+
+      backwardExhausted = true;
+      return iterator();
+    }
+
+    // We tried to fit hunk before text beginning and beyond text length, then
+    // hunk can't fit on the text. Return undefined
+  };
+};
diff --git a/app/assets/javascripts/ide/lib/editor.js b/app/assets/javascripts/ide/lib/editor.js
index 887dd7e39b1..cdb277603f0 100644
--- a/app/assets/javascripts/ide/lib/editor.js
+++ b/app/assets/javascripts/ide/lib/editor.js
@@ -109,6 +109,13 @@ export default class Editor {
     if (this.dirtyDiffController) this.dirtyDiffController.reDecorate(model);
   }
 
+  attachMergeRequestModel(model) {
+    this.instance.setModel({
+      original: model.getTargetModel(),
+      modified: model.getModel(),
+    });
+  }
+
   setupMonacoTheme() {
     this.monaco.editor.defineTheme(
       gitlabTheme.themeName,
diff --git a/app/assets/javascripts/ide/services/index.js b/app/assets/javascripts/ide/services/index.js
index 5f1fb6cf843..46a65c583e0 100644
--- a/app/assets/javascripts/ide/services/index.js
+++ b/app/assets/javascripts/ide/services/index.js
@@ -20,12 +20,19 @@ 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());
   },
   getProjectData(namespace, project) {
     return Api.project(`${namespace}/${project}`);
   },
+  getProjectMergeRequestData(projectId, mergeRequestId) {
+    return Api.mergeRequest(projectId, mergeRequestId);
+  },
+  getProjectMergeRequestChanges(projectId, mergeRequestId) {
+    return Api.mergeRequestChanges(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..83e200f3cc0 100644
--- a/app/assets/javascripts/ide/stores/actions.js
+++ b/app/assets/javascripts/ide/stores/actions.js
@@ -119,3 +119,4 @@ 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..57e036f57af 100644
--- a/app/assets/javascripts/ide/stores/actions/file.js
+++ b/app/assets/javascripts/ide/stores/actions/file.js
@@ -1,10 +1,12 @@
 import { normalizeHeaders } from '~/lib/utils/common_utils';
+import { parsePatch, applyPatches } from 'diff';
+import { revertPatch } from '../../lib/diff/revert_patch';
 import flash from '~/flash';
 import eventHub from '../../eventhub';
 import service from '../../services';
 import * as types from '../mutation_types';
 import router from '../../ide_router';
-import { setPageTitle } from '../utils';
+import { setPageTitle, createTemp, findIndexOfFile } from '../utils';
 
 export const closeFile = ({ commit, state, getters, dispatch }, path) => {
   const indexOfClosedFile = state.openFiles.findIndex(f => f.path === path);
@@ -46,53 +48,140 @@ export const setFileActive = ({ commit, state, getters, dispatch }, path) => {
   commit(types.SET_CURRENT_BRANCH, file.branchId);
 };
 
-export const getFileData = ({ state, commit, dispatch }, file) => {
-  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_LOADING, { entry: file });
-    })
-    .catch(() => {
-      commit(types.TOGGLE_LOADING, { entry: file });
-      flash(
-        'Error loading file data. Please try again.',
-        'alert',
-        document,
-        null,
-        false,
-        true,
-      );
-    });
+export const getFileData = ({ state, commit, dispatch }, path) => {
+  const file = state.entries[path];
+  return new Promise((resolve, reject) => {
+    commit(types.TOGGLE_LOADING, { entry: file });
+    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, path);
+        dispatch('setFileActive', file.path);
+        commit(types.TOGGLE_LOADING, { entry: file });
+      })
+      .catch(err => {
+        console.log('Error : ', err);
+        commit(types.TOGGLE_LOADING, { entry: file });
+        flash(
+          'Error loading file data. Please try again.',
+          'alert',
+          document,
+          null,
+          false,
+          true,
+        );
+      });
+  });
+};
+
+export const preloadFileTab = ({ state, commit, dispatch }, file) => {
+  return new Promise((resolve, reject) => {
+    commit(types.TOGGLE_LOADING, { entry: file });
+    service
+      .getFileData(file.url)
+      .then(data => {
+        commit(types.SET_FILE_DATA, { data, file });
+        commit(types.TOGGLE_FILE_OPEN, file);
+        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,
+        );
+      });
+  });
+};
+
+export const setFileTargetBranch = (
+  { state, commit },
+  { file, targetBranch },
+) => {
+  commit(types.SET_FILE_TARGET_BRANCH, {
+    file,
+    targetBranch,
+    targetRawPath: file.rawPath.replace(file.branchId, targetBranch),
+  });
+};
+
+export const processFileMrDiff = ({ state, commit }, file) => {
+  const patchObj = parsePatch(file.mrDiff);
+  const transformedContent = applyPatch(file.raw, file.mrDiff);
+  debugger;
 };
 
-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 setFileMrDiff = ({ state, commit }, { file, mrDiff }) => {
+  commit(types.SET_FILE_MR_DIFF, { file, mrDiff });
+};
+
+export const getRawFileData = ({ commit, dispatch }, file) => {
+  return new Promise((resolve, reject) => {
+    service
+      .getRawFileData(file)
+      .then(raw => {
+        commit(types.SET_FILE_RAW_DATA, { file, raw });
+        if (file.mrDiff) {
+          const patchObj = parsePatch(file.mrDiff);
+          patchObj[0].hunks.forEach(hunk => {
+            console.log('H ', hunk);
+            /*hunk.lines.forEach((line) => {
+                  if (line.substr(0, 1) === '+') {
+                    line = '-' + line.substr(1);
+                  } else if (line.substr(0, 1) === '-') {
+                    line = '+' + line.substr(1);
+                  }
+                })*/
+          });
+
+          console.log('PATCH OBJ : ' + JSON.stringify(patchObj));
+
+          const transformedContent = revertPatch(raw, patchObj, {
+            compareLine: (lineNumber, line, operation, patchContent) => {
+              const tempLine = line;
+              //line = patchContent;
+              //patchContent = tempLine;
+              if (operation === '-') {
+                operation = '+';
+              } else if (operation === '+') {
+                operation = '-';
+              }
+              console.log(
+                'COMPARE : ' + line + ' - ' + operation + ' - ' + patchContent,
+              );
+              return true;
+            },
+          });
+          console.log('TRANSFORMED : ', transformedContent);
+          commit(types.SET_FILE_TARGET_RAW_DATA, {
+            file,
+            raw: transformedContent,
+          });
+          resolve(raw);
+        } 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];
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..6da00e98f59
--- /dev/null
+++ b/app/assets/javascripts/ide/stores/actions/merge_request.js
@@ -0,0 +1,96 @@
+import flash from '~/flash';
+import service from '../../services';
+import * as types from '../mutation_types';
+
+// eslint-disable-next-line import/prefer-default-export
+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,
+              `${projectId}/${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]);
+    }
+  });
+
+// eslint-disable-next-line import/prefer-default-export
+export const getMergeRequestChanges = (
+  { commit, state, dispatch },
+  { projectId, mergeRequestId, force = false } = {},
+) =>
+  new Promise((resolve, reject) => {
+    if (
+      !state.projects[projectId].mergeRequests[mergeRequestId].changes ||
+      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);
+    }
+  });
+
+// eslint-disable-next-line import/prefer-default-export
+export const getMergeRequestNotes = (
+  { commit, state, dispatch },
+  { projectId, mergeRequestId, force = false } = {},
+) =>
+  new Promise((resolve, reject) => {
+    if (
+      !state.projects[projectId].mergeRequests[mergeRequestId].notes ||
+      force
+    ) {
+      service
+        .getProjectMergeRequestNotes(projectId, mergeRequestId)
+        .then(res => res.data)
+        .then(data => {
+          commit(types.SET_MERGE_REQUEST_NOTES, {
+            projectPath: projectId,
+            mergeRequestId,
+            notes: data,
+          });
+          resolve(data);
+        })
+        .catch(() => {
+          flash('Error loading merge request notes. Please try again.');
+          reject(new Error(`Merge Request Notes not loaded ${projectId}`));
+        });
+    } else {
+      resolve(state.projects[projectId].mergeRequests[mergeRequestId].notes);
+    }
+  });
diff --git a/app/assets/javascripts/ide/stores/actions/tree.js b/app/assets/javascripts/ide/stores/actions/tree.js
index 70a969a0325..4a960a12010 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) => {
@@ -21,24 +19,33 @@ export const handleTreeEntryAction = ({ commit, dispatch }, row) => {
 
     dispatch('setFileActive', row.path);
   } else {
-    dispatch('getFileData', row);
+    dispatch('getFileData', row.path);
   }
 };
 
-export const getLastCommitData = ({ state, commit, dispatch, getters }, tree = state) => {
+export const getLastCommitData = (
+  { state, commit, dispatch, getters },
+  tree = state,
+) => {
   if (!tree || tree.lastCommitPath === null || !tree.lastCommitPath) return;
 
-  service.getTreeLastCommit(tree.lastCommitPath)
-    .then((res) => {
-      const lastCommitPath = normalizeHeaders(res.headers)['MORE-LOGS-URL'] || null;
+  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) => {
-        const entry = findEntry(tree.tree, lastCommit.type, lastCommit.file_name);
+    .then(data => {
+      data.forEach(lastCommit => {
+        const entry = findEntry(
+          tree.tree,
+          lastCommit.type,
+          lastCommit.file_name,
+        );
 
         if (entry) {
           commit(types.SET_LAST_COMMIT_DATA, { entry, lastCommit });
@@ -47,47 +54,62 @@ export const getLastCommitData = ({ state, commit, dispatch, getters }, tree = s
 
       dispatch('getLastCommitData', tree);
     })
-    .catch(() => flash('Error fetching log data.', 'alert', document, null, false, true));
+    .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,
+) =>
+  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..fab12e7e1c6 100644
--- a/app/assets/javascripts/ide/stores/getters.js
+++ b/app/assets/javascripts/ide/stores/getters.js
@@ -28,3 +28,5 @@ 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..4edbc58ca40 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_NOTES = 'SET_MERGE_REQUEST_NOTES';
+
 // 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_TARGET_RAW_DATA = 'SET_FILE_TARGET_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 +46,7 @@ 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_MR_DIFF = 'SET_FILE_MR_DIFF';
+export const SET_FILE_TARGET_BRANCH = 'SET_FILE_TARGET_BRANCH';
 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..a3b9d0dac8c 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';
@@ -100,6 +101,7 @@ 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..1297d3aaf1f 100644
--- a/app/assets/javascripts/ide/stores/mutations/file.js
+++ b/app/assets/javascripts/ide/stores/mutations/file.js
@@ -35,6 +35,11 @@ export default {
       raw,
     });
   },
+  [types.SET_FILE_TARGET_RAW_DATA](state, { file, raw }) {
+    Object.assign(file, {
+      targetRaw: raw,
+    });
+  },
   [types.UPDATE_FILE_CONTENT](state, { path, content }) {
     const changed = content !== state.entries[path].raw;
 
@@ -59,6 +64,16 @@ export default {
       editorColumn,
     });
   },
+  [types.SET_FILE_MR_DIFF](state, { file, mrDiff }) {
+    Object.assign(file, {
+      mrDiff,
+    });
+  },
+  [types.SET_FILE_TARGET_BRANCH](state, { file, targetBranch }) {
+    Object.assign(file, {
+      targetBranch,
+    });
+  },
   [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..69abe010372
--- /dev/null
+++ b/app/assets/javascripts/ide/stores/mutations/merge_request.js
@@ -0,0 +1,40 @@
+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 },
+  ) {
+    // Add client side properties
+    Object.assign(mergeRequest, {
+      active: true,
+    });
+
+    Object.assign(state.projects[projectPath], {
+      mergeRequests: {
+        [mergeRequestId]: mergeRequest,
+      },
+    });
+  },
+  [types.SET_MERGE_REQUEST_CHANGES](
+    state,
+    { projectPath, mergeRequestId, changes },
+  ) {
+    Object.assign(state.projects[projectPath].mergeRequests[mergeRequestId], {
+      changes,
+    });
+  },
+  [types.SET_MERGE_REQUEST_NOTES](
+    state,
+    { projectPath, mergeRequestId, notes },
+  ) {
+    Object.assign(state.projects[projectPath].mergeRequests[mergeRequestId], {
+      notes,
+    });
+  },
+};
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..cb0b1354665 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 +79,45 @@ export const decorateData = (entity) => {
     base64,
 
     file_lock,
-
   };
 };
 
-export const findEntry = (tree, type, name, prop = 'name') => tree.find(
-  f => f.type === type && f[prop] === name,
-);
+/*
+  Takes the multi-dimensional tree and returns a flattened array.
+  This allows for the table to recursively render the table rows but keeps the data
+  structure nested to make it easier to add new files/directories.
+*/
+export const treeList = (state, treeId) => {
+  const baseTree = state.trees[treeId];
+  if (baseTree) {
+    const mapTree = arr =>
+      !arr.tree || !arr.tree.length
+        ? []
+        : _.map(arr.tree, a => [a, mapTree(a)]);
+
+    return _.chain(baseTree.tree)
+      .map(arr => [arr, mapTree(arr)])
+      .flatten()
+      .value();
+  }
+  return [];
+};
+
+export const getTree = state => (namespace, projectId, branch) =>
+  state.trees[`${namespace}/${projectId}/${branch}`];
+
+export const getTreeEntry = (store, treeId, path) => {
+  const fileList = treeList(store.state, treeId);
+  return fileList ? fileList.find(file => file.path === path) : null;
+};
+
+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 findIndexOfFile = (state, file) =>
+  state.findIndex(f => f.path === file.path);
 
-export const setPageTitle = (title) => {
+export const setPageTitle = title => {
   document.title = title;
 };
 
@@ -120,6 +147,11 @@ 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/vue_merge_request_widget/components/mr_widget_header.vue b/app/assets/javascripts/vue_merge_request_widget/components/mr_widget_header.vue
index 3d886e7d628..d3d5ef76d2e 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 +1,62 @@
 <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 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 `${
+        gon.relative_url_root
+      }/-/ide/project${this.mr.statusPath.replace('.json', '')}`;
+    },
+  },
+  methods: {
+    isBranchTitleLong(branchTitle) {
+      return branchTitle.length > 32;
+    },
+  },
+};
 </script>
 <template>
   <div class="mr-source-target">
@@ -96,6 +105,14 @@
     </div>
 
     <div v-if="mr.isOpen">
+      <a
+        :disabled="mr.sourceBranchRemoved"
+        :href="webIdePath"
+        class="btn btn-sm btn-default inline js-web-ide"
+        type="button"
+      >
+        {{ s__("mrWidget|Open in Web IDE") }}
+      </a>
       <button
         data-target="#modal_merge_info"
         data-toggle="modal"