1 files changed, 26 insertions, 8 deletions
diff --git a/app/services/suggestions/apply_service.rb b/app/services/suggestions/apply_service.rb
index d931d528c86..cc47b46b527 100644
--- a/app/services/suggestions/apply_service.rb
+++ b/app/services/suggestions/apply_service.rb
@@ -11,6 +11,10 @@ module Suggestions
         return error('Suggestion is not appliable')
       end
 
+      unless latest_diff_refs?(suggestion)
+        return error('The file has been changed')
+      end
+
       params = file_update_params(suggestion)
       result = ::Files::UpdateService.new(suggestion.project, @current_user, params).execute
 
@@ -19,30 +23,44 @@ module Suggestions
       end
 
       result
+    rescue Files::UpdateService::FileChangedError
+      error('The file has been changed')
     end
 
     private
 
-    def file_update_params(suggestion)
-      diff_file = suggestion.diff_file
+    # Checks whether the latest diff refs for the branch matches with
+    # the position refs we're using to update the file content. Since
+    # the persisted refs are updated async (for MergeRequest),
+    # it's more consistent to fetch this data directly from the repository.
+    def latest_diff_refs?(suggestion)
+      suggestion.position.diff_refs == suggestion.noteable.repository_diff_refs
+    end
 
-      file_path = diff_file.file_path
-      branch_name = suggestion.noteable.source_branch
-      file_content = new_file_content(suggestion)
+    def file_update_params(suggestion)
+      blob = suggestion.diff_file.new_blob
+      file_path = suggestion.file_path
+      branch_name = suggestion.branch
+      file_content = new_file_content(suggestion, blob)
       commit_message = "Apply suggestion to #{file_path}"
 
+      file_last_commit =
+        Gitlab::Git::Commit.last_for_path(suggestion.project.repository,
+                                          blob.commit_id,
+                                          blob.path)
+
       {
         file_path: file_path,
         branch_name: branch_name,
         start_branch: branch_name,
         commit_message: commit_message,
-        file_content: file_content
+        file_content: file_content,
+        last_commit_sha: file_last_commit&.id
       }
     end
 
-    def new_file_content(suggestion)
+    def new_file_content(suggestion, blob)
       range = suggestion.from_line_index..suggestion.to_line_index
-      blob = suggestion.diff_file.new_blob
 
       blob.load_all_data!
       content = blob.data.lines