Merge branch 'legacy-diff-notes-are-dumb' into 'master'

Don't fail when a LegacyDiffNote didn't store the right diff

Fixes https://sentry.gitlap.com/gitlab/gitlabcom/issues/8865/ and https://sentry.gitlap.com/gitlab/gitlabcom/issues/8754/

See merge request !5287

app/models/legacy_diff_note.rb

@@ -38,7 +38,7 @@ class LegacyDiffNote < Note
   end
 
   def diff_line
-    @diff_line ||= diff_file.line_for_line_code(self.line_code)
+    @diff_line ||= diff_file.line_for_line_code(self.line_code) if diff_file
   end
 
   def for_line?(line)
@@ -55,7 +55,7 @@ class LegacyDiffNote < Note
   def active?
     return @active if defined?(@active)
     return true if for_commit?
-    return true unless self.diff
+    return true unless diff_line
     return false unless noteable
 
     noteable_diff = find_noteable_diff

app/views/notify/note_merge_request_email.html.haml

-- if @note.diff_note?
+- if @note.diff_note? && @note.diff_file
   %p.details
     New comment on diff for
     = link_to @note.diff_file.file_path, @target_url

spec/models/legacy_diff_note_spec.rb

@@ -16,10 +16,10 @@ describe LegacyDiffNote, models: true do
   end
 
   describe '#active?' do
-    it 'is always true when the note has no associated diff' do
+    it 'is always true when the note has no associated diff line' do
       note = build(:legacy_diff_note_on_merge_request)
 
-      expect(note).to receive(:diff).and_return(nil)
+      expect(note).to receive(:diff_line).and_return(nil)
 
       expect(note).to be_active
     end
@@ -27,7 +27,7 @@ describe LegacyDiffNote, models: true do
     it 'is never true when the note has no noteable associated' do
       note = build(:legacy_diff_note_on_merge_request)
 
-      expect(note).to receive(:diff).and_return(double)
+      expect(note).to receive(:diff_line).and_return(double)
       expect(note).to receive(:noteable).and_return(nil)
 
       expect(note).not_to be_active
@@ -47,7 +47,7 @@ describe LegacyDiffNote, models: true do
         merge = build_stubbed(:merge_request, :simple)
         note = build(:legacy_diff_note_on_merge_request, noteable: merge)
 
-        allow(note).to receive(:diff).and_return(double)
+        allow(note).to receive(:diff_line).and_return(double)
         expect(note).to receive(:find_noteable_diff).and_return(nil)
 
         expect(note).not_to be_active