Automatically update diff note positions when MR is pushed to

3 files changed, 33 insertions, 3 deletions

diff --git a/app/services/merge_requests/refresh_service.rb b/app/services/merge_requests/refresh_service.rb
index de79c024428..21490ac77ea 100644
--- a/app/services/merge_requests/refresh_service.rb
+++ b/app/services/merge_requests/refresh_service.rb
@@ -60,7 +60,7 @@ module MergeRequests
 
       merge_requests.each do |merge_request|
         if merge_request.source_branch == @branch_name || force_push?
-          merge_request.reload_code
+          merge_request.reload_diff
           merge_request.mark_as_unchecked
         else
           mr_commit_ids = merge_request.commits.map(&:id)
@@ -68,7 +68,7 @@ module MergeRequests
           matches = mr_commit_ids & push_commit_ids
 
           if matches.any?
-            merge_request.reload_code
+            merge_request.reload_diff
             merge_request.mark_as_unchecked
           else
             merge_request.mark_as_unchecked
diff --git a/app/services/merge_requests/reopen_service.rb b/app/services/merge_requests/reopen_service.rb
index 8279ad2001b..eb88ae9d11c 100644
--- a/app/services/merge_requests/reopen_service.rb
+++ b/app/services/merge_requests/reopen_service.rb
@@ -6,7 +6,7 @@ module MergeRequests
         create_note(merge_request)
         notification_service.reopen_mr(merge_request, current_user)
         execute_hooks(merge_request, 'reopen')
-        merge_request.reload_code
+        merge_request.reload_diff
         merge_request.mark_as_unchecked
       end
 
diff --git a/app/services/notes/diff_position_update_service.rb b/app/services/notes/diff_position_update_service.rb
new file mode 100644
index 00000000000..0cb731f5bc3
--- /dev/null
+++ b/app/services/notes/diff_position_update_service.rb
@@ -0,0 +1,30 @@
+module Notes
+  class DiffPositionUpdateService < BaseService
+    def execute(note)
+      new_position = tracer.trace(note.position)
+
+      # Don't update the position if the type doesn't match, since that means
+      # the diff line commented on was changed, and the comment is now outdated
+      old_position = note.position
+      if new_position &&
+          new_position != old_position &&
+          new_position.type == old_position.type
+
+        note.position = new_position
+      end
+
+      note
+    end
+
+    private
+
+    def tracer
+      @tracer ||= Gitlab::Diff::PositionTracer.new(
+        repository: project.repository,
+        old_diff_refs: params[:old_diff_refs],
+        new_diff_refs: params[:new_diff_refs],
+        paths: params[:paths]
+      )
+    end
+  end
+end