Fix image diff notes email

app/views/notify/_note_email.html.haml

 - discussion = @note.discussion if @note.part_of_discussion?
+- diff_discussion = discussion&.diff_discussion?
+- on_image = discussion.on_image? if diff_discussion
+
 - if discussion
+  - phrase_end_char = on_image ? "." : ":"
+
   %p.details
-    = succeed ':' do
+    = succeed phrase_end_char do
       = link_to @note.author_name, user_url(@note.author)
 
-      - if discussion.diff_discussion?
+      - if diff_discussion
         - if discussion.new_discussion?
           started a new discussion
         - else
@@ -21,7 +26,7 @@
   %p.details
     #{link_to @note.author_name, user_url(@note.author)} commented:
 
-- if discussion&.diff_discussion?
+- if diff_discussion && !on_image
   = content_for :head do
     = stylesheet_link_tag 'mailers/highlighted_diff_email'
 

changelogs/unreleased/issue_39238.yml

+---
+title: Fix image diff notification email from showing wrong content
+merge_request:
+author:
+type: fixed

spec/mailers/notify_spec.rb

@@ -783,7 +783,25 @@ describe Notify do
       shared_examples 'an email for a note on a diff discussion' do  |model|
         let(:note) { create(model, author: note_author) }
 
-        it "includes diffs with character-level highlighting" do
+        context 'when note is on image' do
+          before do
+            allow_any_instance_of(DiffDiscussion).to receive(:on_image?).and_return(true)
+          end
+
+          it 'does not include diffs with character-level highlighting' do
+            is_expected.not_to have_body_text '<span class="p">}</span></span>'
+          end
+
+          it 'ends the intro with a dot' do
+            is_expected.to have_body_text "#{note.diff_file.file_path}</a>."
+          end
+        end
+
+        it 'ends the intro with a colon' do
+          is_expected.to have_body_text "#{note.diff_file.file_path}</a>:"
+        end
+
+        it 'includes diffs with character-level highlighting' do
           is_expected.to have_body_text '<span class="p">}</span></span>'
         end