Use last focused markdown field for quoted reply

Fixes a bug where pressing `r` for quoted reply always
added the block quote on main comment form instead
of last opened comment form which can also be
discussion reply form.

Changelog: fixed

app/assets/javascripts/behaviors/shortcuts/shortcuts_issuable.js

@@ -33,10 +33,37 @@ export default class ShortcutsIssuable extends Shortcuts {
     Mousetrap.bind(keysFor(ISSUABLE_COMMENT_OR_REPLY), ShortcutsIssuable.replyWithSelectedText);
     Mousetrap.bind(keysFor(ISSUABLE_EDIT_DESCRIPTION), ShortcutsIssuable.editIssue);
     Mousetrap.bind(keysFor(MR_COPY_SOURCE_BRANCH_NAME), ShortcutsIssuable.copyBranchName);
+
+    /**
+     * We're attaching a global focus event listener on document for
+     * every markdown input field.
+     */
+    $(document).on(
+      'focus',
+      '.js-vue-markdown-field .js-gfm-input',
+      ShortcutsIssuable.handleMarkdownFieldFocus,
+    );
+  }
+
+  /**
+   * This event handler preserves last focused markdown input field.
+   * @param {Object} event
+   */
+  static handleMarkdownFieldFocus({ currentTarget }) {
+    ShortcutsIssuable.$lastFocusedReplyField = $(currentTarget);
   }
 
   static replyWithSelectedText() {
-    const $replyField = $('.js-main-target-form .js-vue-comment-form');
+    let $replyField = $('.js-main-target-form .js-vue-comment-form');
+
+    // Ensure that markdown input is still present in the DOM
+    // otherwise fall back to main comment input field.
+    if (
+      ShortcutsIssuable.$lastFocusedReplyField &&
+      isElementVisible(ShortcutsIssuable.$lastFocusedReplyField?.get(0))
+    ) {
+      $replyField = ShortcutsIssuable.$lastFocusedReplyField;
+    }
 
     if (!$replyField.length || $replyField.is(':hidden') /* Other tab selected in MR */) {
       return false;

spec/features/issuables/shortcuts_issuable_spec.rb

@@ -15,12 +15,20 @@ RSpec.describe 'Blob shortcuts', :js do
   end
 
   shared_examples "quotes the selected text" do
-    it "quotes the selected text", :quarantine do
-      select_element('.note-text')
+    it 'quotes the selected text in main comment form', quarantine: 'https://gitlab.com/gitlab-org/gitlab/-/issues/356388' do
+      select_element('#notes-list .note:first-child .note-text')
       find('body').native.send_key('r')
 
       expect(find('.js-main-target-form .js-vue-comment-form').value).to include(note_text)
     end
+
+    it 'quotes the selected text in the discussion reply form', quarantine: 'https://gitlab.com/gitlab-org/gitlab/-/issues/356388' do
+      find('#notes-list .note:first-child .js-reply-button').click
+      select_element('#notes-list .note:first-child .note-text')
+      find('body').native.send_key('r')
+
+      expect(find('#notes-list .note:first-child .js-vue-markdown-field .js-gfm-input').value).to include(note_text)
+    end
   end
 
   describe 'pressing "r"' do