Raise error when non-dangling builds use YAML blob

Captures invariant that YAML blobs are for dangling builds only.

lib/gitlab/ci/pipeline/chain/command.rb

@@ -90,6 +90,10 @@ module Gitlab
             metrics.pipeline_size_histogram
               .observe({ source: pipeline.source.to_s }, pipeline.total_size)
           end
+
+          def dangling_build?
+            %i[ondemand_dast_scan webide].include?(source)
+          end
         end
       end
     end

lib/gitlab/ci/pipeline/chain/config/content/parameter.rb

@@ -7,9 +7,12 @@ module Gitlab
         module Config
           class Content
             class Parameter < Source
+              UnsupportedSourceError = Class.new(StandardError)
+
               def content
                 strong_memoize(:content) do
                   next unless command.content.present?
+                  raise UnsupportedSourceError, "#{command.source} not a dangling build" unless command.dangling_build?
 
                   command.content
                 end

spec/lib/gitlab/ci/pipeline/chain/command_spec.rb

@@ -270,4 +270,29 @@ RSpec.describe Gitlab::Ci::Pipeline::Chain::Command do
       it { is_expected. to eq(true) }
     end
   end
+
+  describe '#dangling_build?' do
+    let(:project) { create(:project, :repository) }
+    let(:command) { described_class.new(project: project, source: source) }
+
+    subject { command.dangling_build? }
+
+    context 'when source is :webide' do
+      let(:source) { :webide }
+
+      it { is_expected.to eq(true) }
+    end
+
+    context 'when source is :ondemand_dast_scan' do
+      let(:source) { :ondemand_dast_scan }
+
+      it { is_expected.to eq(true) }
+    end
+
+    context 'when source something else' do
+      let(:source) { :web }
+
+      it { is_expected.to eq(false) }
+    end
+  end
 end

spec/lib/gitlab/ci/pipeline/chain/config/content_spec.rb

@@ -6,7 +6,8 @@ RSpec.describe Gitlab::Ci::Pipeline::Chain::Config::Content do
   let(:project) { create(:project, ci_config_path: ci_config_path) }
   let(:pipeline) { build(:ci_pipeline, project: project) }
   let(:content) { nil }
-  let(:command) { Gitlab::Ci::Pipeline::Chain::Command.new(project: project, content: content) }
+  let(:source) { :push }
+  let(:command) { Gitlab::Ci::Pipeline::Chain::Command.new(project: project, content: content, source: source) }
 
   subject { described_class.new(pipeline, command) }
 
@@ -143,6 +144,7 @@ RSpec.describe Gitlab::Ci::Pipeline::Chain::Config::Content do
     end
 
     context 'when config is passed as a parameter' do
+      let(:source) { :ondemand_dast_scan }
       let(:ci_config_path) { nil }
       let(:content) do
         <<~EOY

spec/services/ci/create_pipeline_service/parameter_content_spec.rb

@@ -28,23 +28,34 @@ RSpec.describe Ci::CreatePipelineService do
   end
 
   describe '#execute' do
-    subject { service.execute(:web, content: content) }
+    context 'when source is a dangling build' do
+      subject { service.execute(:ondemand_dast_scan, content: content) }
 
-    context 'parameter config content' do
-      it 'creates a pipeline' do
-        expect(subject).to be_persisted
-      end
+      context 'parameter config content' do
+        it 'creates a pipeline' do
+          expect(subject).to be_persisted
+        end
 
-      it 'creates builds with the correct names' do
-        expect(subject.builds.pluck(:name)).to match_array %w[dast]
-      end
+        it 'creates builds with the correct names' do
+          expect(subject.builds.pluck(:name)).to match_array %w[dast]
+        end
+
+        it 'creates stages with the correct names' do
+          expect(subject.stages.pluck(:name)).to match_array %w[dast]
+        end
 
-      it 'creates stages with the correct names' do
-        expect(subject.stages.pluck(:name)).to match_array %w[dast]
+        it 'sets the correct config source' do
+          expect(subject.config_source).to eq 'parameter_source'
+        end
       end
+    end
+
+    context 'when source is not a dangling build' do
+      subject { service.execute(:web, content: content) }
 
-      it 'sets the correct config source' do
-        expect(subject.config_source).to eq 'parameter_source'
+      it 'raises an exception' do
+        klass = Gitlab::Ci::Pipeline::Chain::Config::Content::Parameter::UnsupportedSourceError
+        expect { subject }.to raise_error(klass)
       end
     end
   end