Fixed issue with discussion not linking to in file-by-file

This was caused by the discussions endpoint being
slower than the diffs endpoint which caused the correct
diff file ID not to be set

app/assets/javascripts/diffs/store/actions.js

@@ -233,9 +233,11 @@ export const setHighlightedRow = ({ commit }, lineCode) => {
 // This is adding line discussions to the actual lines in the diff tree
 // once for parallel and once for inline mode
 export const assignDiscussionsToDiff = (
-  { commit, state, rootState },
+  { commit, state, rootState, dispatch },
   discussions = rootState.notes.discussions,
 ) => {
+  const id = window?.location?.hash;
+  const isNoteLink = id.indexOf('#note') === 0;
   const diffPositionByLineCode = getDiffPositionByLineCode(
     state.diffFiles,
     state.useSingleDiffStyle,
@@ -252,6 +254,10 @@ export const assignDiscussionsToDiff = (
       });
     });
 
+  if (isNoteLink) {
+    dispatch('setCurrentDiffFileIdFromNote', id.split('_').pop());
+  }
+
   Vue.nextTick(() => {
     eventHub.$emit('scrollToDiscussion');
   });
@@ -736,8 +742,11 @@ export function moveToNeighboringCommit({ dispatch, state }, { direction }) {
 }
 
 export const setCurrentDiffFileIdFromNote = ({ commit, rootGetters }, noteId) => {
-  const fileHash = rootGetters.getDiscussion(rootGetters.notesById[noteId].discussion_id).diff_file
-    .file_hash;
+  const note = rootGetters.notesById[noteId];
+
+  if (!note) return;
+
+  const fileHash = rootGetters.getDiscussion(note.discussion_id).diff_file.file_hash;
 
   commit(types.UPDATE_CURRENT_DIFF_FILE_ID, fileHash);
 };

spec/frontend/diffs/store/actions_spec.js

@@ -485,6 +485,10 @@ describe('DiffsStoreActions', () => {
   });
 
   describe('assignDiscussionsToDiff', () => {
+    afterEach(() => {
+      window.location.hash = '';
+    });
+
     it('should merge discussions into diffs', done => {
       window.location.hash = 'ABC_123';
 
@@ -578,6 +582,19 @@ describe('DiffsStoreActions', () => {
         done,
       );
     });
+
+    it('dispatches setCurrentDiffFileIdFromNote with note ID', done => {
+      window.location.hash = 'note_123';
+
+      testAction(
+        assignDiscussionsToDiff,
+        [],
+        { diffFiles: [], useSingleDiffStyle: true },
+        [],
+        [{ type: 'setCurrentDiffFileIdFromNote', payload: '123' }],
+        done,
+      );
+    });
   });
 
   describe('removeDiscussionsFromDiff', () => {