1 files changed, 57 insertions, 0 deletions
diff --git a/app/services/merge_requests/merge_to_ref_service.rb b/app/services/merge_requests/merge_to_ref_service.rb
new file mode 100644
index 00000000000..8670b9ccf3d
--- /dev/null
+++ b/app/services/merge_requests/merge_to_ref_service.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+module MergeRequests
+  # Performs the merge between source SHA and the target branch. Instead
+  # of writing the result to the MR target branch, it targets the `target_ref`.
+  #
+  # Ideally this should leave the `target_ref` state with the same state the
+  # target branch would have if we used the regular `MergeService`, but without
+  # every side-effect that comes with it (MR updates, mails, source branch
+  # deletion, etc). This service should be kept idempotent (i.e. can
+  # be executed regardless of the `target_ref` current state).
+  #
+  class MergeToRefService < MergeRequests::MergeBaseService
+    def execute(merge_request)
+      @merge_request = merge_request
+
+      validate!
+
+      commit_id = commit
+
+      raise_error('Conflicts detected during merge') unless commit_id
+
+      success(commit_id: commit_id)
+    rescue MergeError, ArgumentError => error
+      error(error.message)
+    end
+
+    private
+
+    def validate!
+      error_check!
+    end
+
+    def error_check!
+      super
+
+      error =
+        if !hooks_validation_pass?(merge_request)
+          hooks_validation_error(merge_request)
+        elsif source.blank?
+          'No source for merge'
+        end
+
+      raise_error(error) if error
+    end
+
+    def target_ref
+      merge_request.merge_ref_path
+    end
+
+    def commit
+      repository.merge_to_ref(current_user, source, merge_request, target_ref, commit_message)
+    rescue Gitlab::Git::PreReceiveError => error
+      raise MergeError, error.message
+    end
+  end
+end