Gets syntax highlighting working.

app/assets/javascripts/repo/repo_editor.js

 /* global monaco */
 import Vue from 'vue';
 import Store from './repo_store'
+import Helper from './repo_helper'
 
 export default class RepoEditor {
   constructor() {
@@ -17,6 +18,7 @@ export default class RepoEditor {
           model: null
         }
       )
+      Helper.monacoInstance = monaco;
       this.initVue();
     });
   }
@@ -59,7 +61,7 @@ export default class RepoEditor {
             self.monacoEditor.setModel(
               monaco.editor.createModel(
                 this.blobRaw,
-                'plain'
+                this.activeFile.mime_type
               )
             );
           }

app/assets/javascripts/repo/repo_helper.js

@@ -6,12 +6,14 @@ let RepoHelper = {
     return data.hasOwnProperty('blobs');
   },
 
+  monacoInstance: undefined,
+
   Time: window.performance
   && window.performance.now
   ? window.performance
   : Date,
 
-  getLanguagesForMimeType(mimetypeNeedle, monaco) {
+  getLanguagesForMimeType(mimetypeNeedle) {
     const langs = monaco.languages.getLanguages();
     let lang = '';
     langs.every((lang) => {
@@ -62,6 +64,9 @@ let RepoHelper = {
   setActiveFile(file) {
     Store.openedFiles = Store.openedFiles.map((openedFile) => {
       openedFile.active = file.url === openedFile.url;
+      if(openedFile.active) {
+        Store.activeFile = openedFile;
+      }
       return openedFile;
     });
     Store.blobRaw = file.plain;

app/assets/javascripts/repo/repo_store.js

@@ -10,6 +10,7 @@ let RepoStore = {
   blobRaw: '',
   blobRendered: '',
   openedFiles: [],
+  activeFile: '',
   files: []
 };
 export default RepoStore;