Fix CI_COMMIT_REF_NAME and SLUG variable

With Pipelines for Merge Requests feature, users cannout keep using
$CI_COMMIT_REF_NAME and _SLUG predefined variables for dynamic
environments. We fix this problem by explicitly looking at the source
ref.

6 files changed, 42 insertions, 8 deletions

diff --git a/app/models/ci/bridge.rb b/app/models/ci/bridge.rb
index 0d8d7d95791..644716ba8e7 100644
--- a/app/models/ci/bridge.rb
+++ b/app/models/ci/bridge.rb
@@ -4,6 +4,7 @@ module Ci
   class Bridge < CommitStatus
     include Ci::Processable
     include Ci::Contextable
+    include Ci::PipelineDelegator
     include Importable
     include AfterCommitQueue
     include HasRef
@@ -13,8 +14,6 @@ module Ci
     belongs_to :trigger_request
     validates :ref, presence: true
 
-    delegate :merge_request_event?, to: :pipeline
-
     def self.retry(bridge, current_user)
       raise NotImplementedError
     end
diff --git a/app/models/ci/build.rb b/app/models/ci/build.rb
index e5236051118..5a2ead41578 100644
--- a/app/models/ci/build.rb
+++ b/app/models/ci/build.rb
@@ -6,6 +6,7 @@ module Ci
     include Ci::Processable
     include Ci::Metadatable
     include Ci::Contextable
+    include Ci::PipelineDelegator
     include TokenAuthenticatable
     include AfterCommitQueue
     include ObjectStorage::BackgroundMove
@@ -49,8 +50,6 @@ 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?, :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 bbd21eb0e78..2b7835d7fab 100644
--- a/app/models/ci/pipeline.rb
+++ b/app/models/ci/pipeline.rb
@@ -759,6 +759,18 @@ module Ci
       user == current_user
     end
 
+    def source_ref
+      if triggered_by_merge_request?
+        merge_request.source_branch
+      else
+        ref
+      end
+    end
+
+    def source_ref_slug
+      Gitlab::Utils.slugify(source_ref.to_s)
+    end
+
     private
 
     def ci_yaml_from_repo
diff --git a/app/models/concerns/ci/contextable.rb b/app/models/concerns/ci/contextable.rb
index 4986a42dbd2..e1d5ce7f7d4 100644
--- a/app/models/concerns/ci/contextable.rb
+++ b/app/models/concerns/ci/contextable.rb
@@ -70,8 +70,8 @@ module Ci
         variables.append(key: 'CI_COMMIT_SHA', value: sha)
         variables.append(key: 'CI_COMMIT_SHORT_SHA', value: short_sha)
         variables.append(key: 'CI_COMMIT_BEFORE_SHA', value: before_sha)
-        variables.append(key: 'CI_COMMIT_REF_NAME', value: ref)
-        variables.append(key: 'CI_COMMIT_REF_SLUG', value: ref_slug)
+        variables.append(key: 'CI_COMMIT_REF_NAME', value: source_ref)
+        variables.append(key: 'CI_COMMIT_REF_SLUG', value: source_ref_slug)
         variables.append(key: "CI_COMMIT_TAG", value: ref) if tag?
         variables.append(key: "CI_PIPELINE_TRIGGERED", value: 'true') if trigger_request
         variables.append(key: "CI_JOB_MANUAL", value: 'true') if action?
@@ -85,8 +85,8 @@ module Ci
       Gitlab::Ci::Variables::Collection.new.tap do |variables|
         variables.append(key: 'CI_BUILD_REF', value: sha)
         variables.append(key: 'CI_BUILD_BEFORE_SHA', value: before_sha)
-        variables.append(key: 'CI_BUILD_REF_NAME', value: ref)
-        variables.append(key: 'CI_BUILD_REF_SLUG', value: ref_slug)
+        variables.append(key: 'CI_BUILD_REF_NAME', value: source_ref)
+        variables.append(key: 'CI_BUILD_REF_SLUG', value: source_ref_slug)
         variables.append(key: 'CI_BUILD_NAME', value: name)
         variables.append(key: 'CI_BUILD_STAGE', value: stage)
         variables.append(key: "CI_BUILD_TAG", value: ref) if tag?
diff --git a/app/models/concerns/ci/pipeline_delegator.rb b/app/models/concerns/ci/pipeline_delegator.rb
new file mode 100644
index 00000000000..dbc5ed1bc9a
--- /dev/null
+++ b/app/models/concerns/ci/pipeline_delegator.rb
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+##
+# This module is mainly used by child associations of `Ci::Pipeline` that needs to look up
+# single source of truth. For example, `Ci::Build` has `git_ref` method, which behaves
+# slightly different from `Ci::Pipeline`'s `git_ref`. This is very confusing as
+# the system could behave differently time to time.
+# We should have a single interface in `Ci::Pipeline` and access the method always.
+module Ci
+  module PipelineDelegator
+    extend ActiveSupport::Concern
+
+    included do
+      delegate :merge_request_event?,
+               :merge_request_ref?,
+               :source_ref,
+               :source_ref_slug,
+               :legacy_detached_merge_request_pipeline?, to: :pipeline
+    end
+  end
+end
diff --git a/app/models/concerns/has_ref.rb b/app/models/concerns/has_ref.rb
index 413cd36dcaa..fa0cf5ddfd2 100644
--- a/app/models/concerns/has_ref.rb
+++ b/app/models/concerns/has_ref.rb
@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 
+##
+# We will disable `ref` and `sha` attributes in `Ci::Build` in the future
+# and remove this module in favor of Ci::PipelineDelegator.
 module HasRef
   extend ActiveSupport::Concern