Danger: Fix CiJobsDependencyValidation when YAML cannot be retrieved

In case of an API error, merged YAML should be an empty Hash and not
empty Array. This API error can occur on forks because we cannot lint CI
config on forks.

spec/tooling/danger/ci_jobs_dependency_validation_spec.rb

@@ -112,12 +112,47 @@
         it_behaves_like 'empty message'
       end
 
+      context 'when retrieving target branch jobs fails' do
+        before do
+          allow(ci_jobs_dependency_validation).to receive_message_chain(:gitlab, :api, :get)
+            .with("/projects/1/ci/lint", query: query).and_raise('404 Not Found')
+        end
+
+        it 'prints the failure but does not break' do
+          expect { expect(ci_jobs_dependency_validation.output_message).to eq('') }.tap do |expectation|
+            expectation
+              .to output(<<~MSG).to_stdout
+                Initializing 1 jobs from master ci config...
+                404 Not Found
+                Initializing 0 jobs from feature_branch ci config...
+              MSG
+          end
+        end
+      end
+
       context 'when source branch jobs is empty' do
         let(:master_merged_yaml) { YAML.dump({}) }
 
         it_behaves_like 'empty message'
       end
 
+      context 'when retrieving source branch jobs fails' do
+        before do
+          allow(ci_jobs_dependency_validation).to receive_message_chain(:gitlab, :api, :get)
+            .with("/projects/1/ci/lint", query: {}).and_raise('404 Not Found')
+        end
+
+        it 'prints the failure but does not break' do
+          expect { expect(ci_jobs_dependency_validation.output_message).to eq('') }.tap do |expectation|
+            expectation
+              .to output(<<~MSG).to_stdout
+                404 Not Found
+                Initializing 0 jobs from master ci config...
+              MSG
+          end
+        end
+      end
+
       context 'when jobs do not have dependencies' do
         it_behaves_like 'empty message', :default_stdout_output, 1, 4
       end
@@ -331,7 +366,7 @@
       end
 
       it 'returns jobs yaml' do
-        expect(ci_jobs_dependency_validation.send(:fetch_jobs_yaml, '1', 'master')).to eq([])
+        expect(ci_jobs_dependency_validation.send(:fetch_jobs_yaml, '1', 'master')).to eq({})
       end
     end
 
@@ -343,7 +378,7 @@
       end
 
       it 'returns jobs yaml' do
-        expect(ci_jobs_dependency_validation.send(:fetch_jobs_yaml, '1', 'master')).to eq([])
+        expect(ci_jobs_dependency_validation.send(:fetch_jobs_yaml, '1', 'master')).to eq({})
       end
     end
 
@@ -357,7 +392,7 @@
       end
 
       it 'returns jobs yaml' do
-        expect(ci_jobs_dependency_validation.send(:fetch_jobs_yaml, '1', 'master')).to eq([])
+        expect(ci_jobs_dependency_validation.send(:fetch_jobs_yaml, '1', 'master')).to eq({})
       end
     end
   end

tooling/danger/ci_jobs_dependency_validation.rb

@@ -71,7 +71,7 @@ def fetch_jobs_yaml(project_id, ref)
         YAML.load(api_response['merged_yaml'], aliases: true)
       rescue StandardError => e
         puts e.message
-        []
+        {}
       end
 
       def build_jobs_from_yaml(jobs_yaml, ref)