Trim first char of diff line text on diff discussions

Before, diff file `higlighted_diff_lines`/`parallel_diff_lines` and
diff discussion `truncated_diff_lines` were inconsistent: `text` and
`rich_text` on the latter included the leading +/-/<space> character,
like on the backend, while the former had no `text` and its `rich_text`
had dropped this char.

This resulted in a bug when the suggestions feature expected these diff
line objects to be identical in format and thus interchangeable, which
was not the case.

2 files changed, 9 insertions, 2 deletions

diff --git a/app/assets/javascripts/notes/stores/mutations.js b/app/assets/javascripts/notes/stores/mutations.js
index 8992454be2e..33d39ad2ec9 100644
--- a/app/assets/javascripts/notes/stores/mutations.js
+++ b/app/assets/javascripts/notes/stores/mutations.js
@@ -105,7 +105,10 @@ export default {
 
       if (discussion.diff_file) {
         diffData.file_hash = discussion.diff_file.file_hash;
-        diffData.truncated_diff_lines = discussion.truncated_diff_lines || [];
+
+        diffData.truncated_diff_lines = utils.prepareDiffLines(
+          discussion.truncated_diff_lines || [],
+        );
       }
 
       // To support legacy notes, should be very rare case.
@@ -243,7 +246,7 @@ export default {
   [types.SET_DISCUSSION_DIFF_LINES](state, { discussionId, diffLines }) {
     const discussion = utils.findNoteObjectById(state.discussions, discussionId);
 
-    discussion.truncated_diff_lines = diffLines;
+    discussion.truncated_diff_lines = utils.prepareDiffLines(diffLines);
   },
 
   [types.DISABLE_COMMENTS](state, value) {
diff --git a/app/assets/javascripts/notes/stores/utils.js b/app/assets/javascripts/notes/stores/utils.js
index dd57539e4d8..4b0feb0f94d 100644
--- a/app/assets/javascripts/notes/stores/utils.js
+++ b/app/assets/javascripts/notes/stores/utils.js
@@ -1,4 +1,5 @@
 import AjaxCache from '~/lib/utils/ajax_cache';
+import { trimFirstCharOfLineContent } from '~/diffs/store/utils';
 
 const REGEX_QUICK_ACTIONS = /^\/\w+.*$/gm;
 
@@ -28,3 +29,6 @@ export const getQuickActionText = note => {
 export const hasQuickActions = note => REGEX_QUICK_ACTIONS.test(note);
 
 export const stripQuickActions = note => note.replace(REGEX_QUICK_ACTIONS, '').trim();
+
+export const prepareDiffLines = diffLines =>
+  diffLines.map(line => ({ ...trimFirstCharOfLineContent(line) }));