Change diff highlight/truncate for reusability

Previously the `truncated_diff_lines` method for outputting a discussion diff took in already highlighted lines, which meant it wasn't reuseable for truncating ANY lines. In the way it was used, it also meant that for any email truncation, the whole diff was being highlighted before being truncated, meaning wasted time highlighting lines that wouldn't even be used (granted, they were being memoized, so perhaps this wasn't that great of an issue). I refactored truncation away from highlighting, in order to truncate formatted diffs for text templates in email, using `>`s to designate each line, but otherwise retaining the parsing already done to create `diff_lines`.

Additionally, while notes on merge requests or commits had already been tested, there was no existing test for notes on a diff on an MR or commit. Added mailer tests for such, and a unit test for truncating diff lines.

6 files changed, 17 insertions, 12 deletions

diff --git a/app/views/notify/_note_mr_or_commit_email.html.haml b/app/views/notify/_note_mr_or_commit_email.html.haml
index 3e2046aa9cf..7033842b557 100644
--- a/app/views/notify/_note_mr_or_commit_email.html.haml
+++ b/app/views/notify/_note_mr_or_commit_email.html.haml
@@ -1,15 +1,16 @@
 = content_for :head do
   = stylesheet_link_tag 'mailers/highlighted_diff_email'
 
-- if note.diff_note? && note.diff_file
-  = link_to note.diff_file.file_path, @target_url, class: 'details'
+- if @note.diff_note? && @note.diff_file
+  on
+  = link_to @note.diff_file.file_path, @target_url, class: 'details'
   \:
 
   %table
     = render partial: "projects/diffs/line",
-      collection: discussion.truncated_diff_lines,
+      collection: @discussion.highlighted_diff_lines(@discussion.truncated_diff_lines),
       as: :line,
-      locals: { diff_file: note.diff_file,
+      locals: { diff_file: @note.diff_file,
       plain: true,
       email: true }
 
diff --git a/app/views/notify/_simple_diff.text.erb b/app/views/notify/_simple_diff.text.erb
new file mode 100644
index 00000000000..a5a796bc168
--- /dev/null
+++ b/app/views/notify/_simple_diff.text.erb
@@ -0,0 +1,4 @@
+<% lines = @discussion.truncated_diff_lines %>
+<% @discussion.text_parsed_diff_lines(lines).each do |line| %>
+  <%= line %>
+<% end %>
diff --git a/app/views/notify/note_commit_email.html.haml b/app/views/notify/note_commit_email.html.haml
index f4293a3aa50..17dcf36689f 100644
--- a/app/views/notify/note_commit_email.html.haml
+++ b/app/views/notify/note_commit_email.html.haml
@@ -1,7 +1,5 @@
 %p.details
   New comment for Commit
   = @commit.short_id
-  on
-  = render partial: 'note_mr_or_commit_email',
-    locals: { note: @note,
-    discussion: @discussion}
+
+  = render 'note_mr_or_commit_email'
diff --git a/app/views/notify/note_commit_email.text.erb b/app/views/notify/note_commit_email.text.erb
index a1ef9858021..715e58af61c 100644
--- a/app/views/notify/note_commit_email.text.erb
+++ b/app/views/notify/note_commit_email.text.erb
@@ -2,6 +2,8 @@ New comment for Commit <%= @commit.short_id %>
 
 <%= url_for(namespace_project_commit_url(@note.project.namespace, @note.project, id: @commit.id, anchor: "note_#{@note.id}")) %>
 
+<%= render 'simple_diff' if @discussion %>
+
 <% if current_application_settings.email_author_in_body %>
   <%= @note.author_name %> wrote:
 <% end %>
diff --git a/app/views/notify/note_merge_request_email.html.haml b/app/views/notify/note_merge_request_email.html.haml
index 75250b0383d..b7758f191dc 100644
--- a/app/views/notify/note_merge_request_email.html.haml
+++ b/app/views/notify/note_merge_request_email.html.haml
@@ -1,7 +1,5 @@
 %p.details
   New comment for Merge Request
   = @merge_request.to_reference
-  on
-  = render partial: 'note_mr_or_commit_email',
-    locals: { note: @note,
-    discussion: @discussion}
+
+  = render 'note_mr_or_commit_email'
diff --git a/app/views/notify/note_merge_request_email.text.erb b/app/views/notify/note_merge_request_email.text.erb
index 42d29b34ebc..d24e15af91f 100644
--- a/app/views/notify/note_merge_request_email.text.erb
+++ b/app/views/notify/note_merge_request_email.text.erb
@@ -2,6 +2,8 @@ New comment for Merge Request <%= @merge_request.to_reference %>
 
 <%= url_for(namespace_project_merge_request_url(@merge_request.target_project.namespace, @merge_request.target_project, @merge_request, anchor: "note_#{@note.id}")) %>
 
+<%= render 'simple_diff' if @discussion %>
+
 <% if current_application_settings.email_author_in_body %>
   <%= @note.author_name %> wrote:
 <% end %>