Add system note with link to diff comparison when MR discussion becomes outdated

6 files changed, 35 insertions, 31 deletions

diff --git a/app/models/diff_discussion.rb b/app/models/diff_discussion.rb
index 14ddd2fcc88..800574d8be0 100644
--- a/app/models/diff_discussion.rb
+++ b/app/models/diff_discussion.rb
@@ -19,21 +19,9 @@ class DiffDiscussion < Discussion
 
   def merge_request_version_params
     return unless for_merge_request?
+    return {} if active?
 
-    if active?
-      {}
-    else
-      diff_refs = position.diff_refs
-
-      if diff = noteable.merge_request_diff_for(diff_refs)
-        { diff_id: diff.id }
-      elsif diff = noteable.merge_request_diff_for(diff_refs.head_sha)
-        {
-          diff_id: diff.id,
-          start_sha: diff_refs.start_sha
-        }
-      end
-    end
+    noteable.version_params_for(position.diff_refs)
   end
 
   def reply_attributes
diff --git a/app/models/diff_note.rb b/app/models/diff_note.rb
index 76c59199afd..1764004078e 100644
--- a/app/models/diff_note.rb
+++ b/app/models/diff_note.rb
@@ -8,6 +8,7 @@ class DiffNote < Note
 
   serialize :original_position, Gitlab::Diff::Position
   serialize :position, Gitlab::Diff::Position
+  serialize :change_position, Gitlab::Diff::Position
 
   validates :original_position, presence: true
   validates :position, presence: true
@@ -25,7 +26,7 @@ class DiffNote < Note
     DiffDiscussion
   end
 
-  %i(original_position position).each do |meth|
+  %i(original_position position change_position).each do |meth|
     define_method "#{meth}=" do |new_position|
       if new_position.is_a?(String)
         new_position = JSON.parse(new_position) rescue nil
@@ -36,6 +37,8 @@ class DiffNote < Note
         new_position = Gitlab::Diff::Position.new(new_position)
       end
 
+      return if new_position == read_attribute(meth)
+
       super(new_position)
     end
   end
@@ -45,7 +48,7 @@ class DiffNote < Note
   end
 
   def diff_line
-    @diff_line ||= diff_file.line_for_position(self.original_position) if diff_file
+    @diff_line ||= diff_file&.line_for_position(self.original_position)
   end
 
   def for_line?(line)
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 9be00880438..2eec013fa9d 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -416,13 +416,24 @@ class MergeRequest < ActiveRecord::Base
     @merge_request_diffs_by_diff_refs_or_sha[diff_refs_or_sha]
   end
 
+  def version_params_for(diff_refs)
+    if diff = merge_request_diff_for(diff_refs)
+      { diff_id: diff.id }
+    elsif diff = merge_request_diff_for(diff_refs.head_sha)
+      {
+        diff_id: diff.id,
+        start_sha: diff_refs.start_sha
+      }
+    end
+  end
+
   def reload_diff_if_branch_changed
     if source_branch_changed? || target_branch_changed?
       reload_diff
     end
   end
 
-  def reload_diff
+  def reload_diff(current_user = nil)
     return unless open?
 
     old_diff_refs = self.diff_refs
@@ -432,7 +443,8 @@ class MergeRequest < ActiveRecord::Base
 
     update_diff_notes_positions(
       old_diff_refs: old_diff_refs,
-      new_diff_refs: new_diff_refs
+      new_diff_refs: new_diff_refs,
+      current_user: current_user
     )
   end
 
@@ -861,7 +873,7 @@ class MergeRequest < ActiveRecord::Base
     diff_sha_refs && diff_sha_refs.complete?
   end
 
-  def update_diff_notes_positions(old_diff_refs:, new_diff_refs:)
+  def update_diff_notes_positions(old_diff_refs:, new_diff_refs:, current_user: nil)
     return unless has_complete_diff_refs?
     return if new_diff_refs == old_diff_refs
 
@@ -875,7 +887,7 @@ class MergeRequest < ActiveRecord::Base
 
     service = Notes::DiffPositionUpdateService.new(
       self.project,
-      nil,
+      current_user,
       old_diff_refs: old_diff_refs,
       new_diff_refs: new_diff_refs,
       paths: paths
diff --git a/app/models/merge_request_diff.rb b/app/models/merge_request_diff.rb
index f0a3c30ea74..6e3917a10a3 100644
--- a/app/models/merge_request_diff.rb
+++ b/app/models/merge_request_diff.rb
@@ -175,12 +175,11 @@ class MergeRequestDiff < ActiveRecord::Base
     self == merge_request.merge_request_diff
   end
 
-  def compare_with(sha, straight: true)
+  def compare_with(sha)
     # When compare merge request versions we want diff A..B instead of A...B
     # so we handle cases when user does squash and rebase of the commits between versions.
     # For this reason we set straight to true by default.
-    CompareService.new(project, head_commit_sha)
-      .execute(project, sha, straight: straight)
+    CompareService.new(project, head_commit_sha).execute(project, sha, straight: true)
   end
 
   def commits_count
diff --git a/app/models/note.rb b/app/models/note.rb
index 46d0a4f159f..b4228cc6492 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -121,16 +121,17 @@ class Note < ActiveRecord::Base
     end
 
     def grouped_diff_discussions(diff_refs = nil)
-      groups = {}
+      groups = Hash.new { |h, k| h[k] = [] }
 
       diff_notes.fresh.discussions.each do |discussion|
-        if discussion.active?(diff_refs)
-          discussions = groups[discussion.line_code] ||= []
-        elsif diff_refs && discussion.created_at_diff?(diff_refs)
-          discussions = groups[discussion.original_line_code] ||= []
-        end
-
-        discussions << discussion if discussions
+        line_code =
+          if discussion.active?(diff_refs)
+            discussion.line_code
+          elsif diff_refs && discussion.created_at_diff?(diff_refs)
+            discussion.original_line_code
+          end
+
+        groups[line_code] << discussion if line_code
       end
 
       groups
diff --git a/app/models/system_note_metadata.rb b/app/models/system_note_metadata.rb
index b44f4fe000c..414c95f7705 100644
--- a/app/models/system_note_metadata.rb
+++ b/app/models/system_note_metadata.rb
@@ -2,6 +2,7 @@ class SystemNoteMetadata < ActiveRecord::Base
   ICON_TYPES = %w[
     commit description merge confidential visible label assignee cross_reference
     title time_tracking branch milestone discussion task moved opened closed merged
+    outdated
   ].freeze
 
   validates :note, presence: true