Set a pipeline failure reason when it has YAML errors

app/models/ci/pipeline.rb

@@ -59,7 +59,8 @@ module Ci
     }
 
     enum failure_reason: {
-      unknown_failure: 0
+      unknown_failure: 0,
+      config_error: 1
     }
 
     state_machine :status, initial: :created do

lib/gitlab/ci/pipeline/chain/validate/config.rb

@@ -13,7 +13,7 @@ module Gitlab
                 end
 
                 if @command.save_incompleted && @pipeline.has_yaml_errors?
-                  @pipeline.drop
+                  @pipeline.drop!(:config_error)
                 end
 
                 return error(@pipeline.yaml_errors)

spec/lib/gitlab/ci/pipeline/chain/validate/config_spec.rb

@@ -55,6 +55,10 @@ describe Gitlab::Ci::Pipeline::Chain::Validate::Config do
       it 'fails the pipeline' do
         expect(pipeline.reload).to be_failed
       end
+
+      it 'sets a config error failure reason' do
+        expect(pipeline.reload.config_error?).to eq true
+      end
     end
 
     context 'when saving incomplete pipeline is not allowed' do