Create detached merge request pipelines

By using `refs/merge-requests/:iid/head`

ok

ok

Improve naming nicely

Add nice tests

add nice tests

fix some more

revert

3 files changed, 16 insertions, 2 deletions

diff --git a/app/models/ci/build.rb b/app/models/ci/build.rb
index 59f47effff7..1bd517641ac 100644
--- a/app/models/ci/build.rb
+++ b/app/models/ci/build.rb
@@ -26,7 +26,8 @@ module Ci
     belongs_to :erased_by, class_name: 'User'
 
     RUNNER_FEATURES = {
-      upload_multiple_artifacts: -> (build) { build.publishes_artifacts_reports? }
+      upload_multiple_artifacts: -> (build) { build.publishes_artifacts_reports? },
+      refspecs: -> (build) { build.merge_request_ref? }
     }.freeze
 
     has_one :deployment, as: :deployable, class_name: 'Deployment'
@@ -47,7 +48,8 @@ module Ci
     delegate :terminal_specification, to: :runner_session, allow_nil: true
     delegate :gitlab_deploy_token, to: :project
     delegate :trigger_short_token, to: :trigger_request, allow_nil: true
-    delegate :merge_request_event?, to: :pipeline
+    delegate :merge_request_event?, :merge_request_ref?,
+             :legacy_detached_merge_request_pipeline?, to: :pipeline
 
     ##
     # Since Gitlab 11.5, deployments records started being created right after
diff --git a/app/models/ci/pipeline.rb b/app/models/ci/pipeline.rb
index 826b3f82bbf..e6da0a58dce 100644
--- a/app/models/ci/pipeline.rb
+++ b/app/models/ci/pipeline.rb
@@ -738,6 +738,10 @@ module Ci
       triggered_by_merge_request? && target_sha.nil?
     end
 
+    def legacy_detached_merge_request_pipeline?
+      detached_merge_request_pipeline? && !merge_request_ref?
+    end
+
     def merge_request_pipeline?
       triggered_by_merge_request? && target_sha.present?
     end
@@ -746,6 +750,10 @@ module Ci
       triggered_by_merge_request? && target_sha == merge_request.target_branch_sha
     end
 
+    def merge_request_ref?
+      MergeRequest.merge_request_ref?(ref)
+    end
+
     def matches_sha_or_source_sha?(sha)
       self.sha == sha || self.source_sha == sha
     end
diff --git a/app/models/merge_request.rb b/app/models/merge_request.rb
index 19557fd476e..7135cf58e33 100644
--- a/app/models/merge_request.rb
+++ b/app/models/merge_request.rb
@@ -1129,6 +1129,10 @@ class MergeRequest < ActiveRecord::Base
     "refs/#{Repository::REF_MERGE_REQUEST}/#{iid}/merge"
   end
 
+  def self.merge_request_ref?(ref)
+    ref.start_with?("refs/#{Repository::REF_MERGE_REQUEST}/")
+  end
+
   def in_locked_state
     begin
       lock_mr