Use temporary compare commits when MR not persisted

app/models/merge_request.rb

@@ -787,21 +787,19 @@ class MergeRequest < ActiveRecord::Base
   def all_pipelines
     return unless source_project
 
-    @all_pipelines ||= begin
-      sha = if persisted?
-              all_commits_sha
-            else
-              diff_head_sha
-            end
-
-      source_project.pipelines.order(id: :desc).
-        where(sha: sha, ref: source_branch)
-    end
+    @all_pipelines ||= source_project.pipelines
+        .where(sha: all_commits_sha, ref: source_branch)
+        .order(id: :desc)
   end
 
   # Note that this could also return SHA from now dangling commits
+  #
   def all_commits_sha
+    if persisted?
       merge_request_diffs.flat_map(&:commits_sha).uniq
+    else
+      compare_commits.reverse.map(&:id)
+    end
   end
 
   def merge_commit