Fix self referencing anchors should cause error (#132)

pkg/model/anchors.go

@@ -6,25 +6,33 @@ import (
 	"gopkg.in/yaml.v3"
 )
 
-// Assumes there is no cycle ensured via test TestVerifyCycleIsInvalid
+func resolveAliasesExt(node *yaml.Node, path map[*yaml.Node]bool, skipCheck bool) error {
-func resolveAliases(node *yaml.Node) error {
+	if !skipCheck && path[node] {
+		return errors.New("circular alias")
+	}
 	switch node.Kind {
 	case yaml.AliasNode:
 		aliasTarget := node.Alias
 		if aliasTarget == nil {
 			return errors.New("unresolved alias node")
 		}
+		path[node] = true
 		*node = *aliasTarget
-		if err := resolveAliases(node); err != nil {
+		if err := resolveAliasesExt(node, path, true); err != nil {
 			return err
 		}
+		delete(path, aliasTarget)
 
 	case yaml.DocumentNode, yaml.MappingNode, yaml.SequenceNode:
 		for _, child := range node.Content {
-			if err := resolveAliases(child); err != nil {
+			if err := resolveAliasesExt(child, path, false); err != nil {
 				return err
 			}
 		}
 	}
 	return nil
 }
+
+func resolveAliases(node *yaml.Node) error {
+	return resolveAliasesExt(node, map[*yaml.Node]bool{}, false)
+}

pkg/model/anchors_test.go

@@ -19,6 +19,17 @@ b: &b
 	assert.Error(t, err)
 }
 
+func TestVerifyCycleIsInvalid2(t *testing.T) {
+	var node yaml.Node
+	err := yaml.Unmarshal([]byte(`
+a: &a
+  ref: *a
+`), &node)
+	assert.NoError(t, err)
+	err = resolveAliases(&node)
+	assert.Error(t, err)
+}
+
 func TestVerifyNilAliasError(t *testing.T) {
 	var node yaml.Node
 	err := yaml.Unmarshal([]byte(`