support yaml anchors (#65)

pkg/schema/schema.go

@@ -238,6 +238,9 @@ func (s *Node) UnmarshalYAML(node *yaml.Node) error {
 	if node != nil && node.Kind == yaml.DocumentNode {
 		return s.UnmarshalYAML(node.Content[0])
 	}
+	if node.Kind == yaml.AliasNode {
+		node = node.Alias
+	}
 	def := s.Schema.GetDefinition(s.Definition)
 	if s.Context == nil {
 		s.Context = def.Context

pkg/schema/schema_test.go

@@ -90,3 +90,30 @@ jobs:
 	}).UnmarshalYAML(&node)
 	assert.NoError(t, err)
 }
+
+func TestYAMLAnchors(t *testing.T) {
+	var node yaml.Node
+	err := yaml.Unmarshal([]byte(`
+on: push
+jobs:
+  job-with-condition:
+    runs-on: &label
+      self-hosted
+    if: success() || success('joba', 'jobb') || failure() || failure('joba', 'jobb') || always() || cancelled()
+    steps: &steps
+    - run: exit 0
+  then:
+    runs-on: *label
+    steps:
+    - run: exit 0
+
+`), &node)
+	if !assert.NoError(t, err) {
+		return
+	}
+	err = (&Node{
+		Definition: "workflow-root-strict",
+		Schema:     GetWorkflowSchema(),
+	}).UnmarshalYAML(&node)
+	assert.NoError(t, err)
+}