Add YAML anchor/alias expansion.

kyaml/kio/byteio_reader_test.go

@@ -808,15 +808,13 @@ items:
 	}
 }
 
-// This test is just an exploration of the low level (go-yaml)
-// representation of a small doc with an anchor. The anchor
-// structure is there, in the sense that an alias pointer is
-// readily available when a node's kind is an AliasNode.
-// That is, the anchor mapping has already been recognized.
-// However, the github.com/go-yaml/yaml/encoder.go code doesn't
-// appear to have an option to perform anchor replacements when
-// encoding (instead it emits the anchor definitions and
-// references, which is not a bad thing but not desired here).
+// This test shows the lower level (go-yaml) representation of a small doc
+// with an anchor. The anchor structure is there, in the sense that an
+// alias pointer is readily available when a node's kind is an AliasNode.
+// I.e. the anchor mapping name -> object was noted during unmarshalling.
+// However, at the time of writing github.com/go-yaml/yaml/encoder.go
+// doesn't appear to have an option to perform anchor replacements when
+// encoding.  It emits anchor definitions and references (aliases) intact.
 func TestByteReader_AnchorBehavior(t *testing.T) {
 	const input = `
 data:

kyaml/yaml/rnode.go

@@ -903,6 +903,48 @@ func (rn *RNode) UnmarshalJSON(b []byte) error {
 	return nil
 }
 
+// DeAnchor inflates all YAML aliases with their anchor values.
+// All YAML anchor data is permanently removed (feel free to call Copy first).
+func (rn *RNode) DeAnchor() (err error) {
+	rn.value, err = deAnchor(rn.value)
+	return
+}
+
+// deAnchor removes all AliasNodes from the yaml.Node's tree, replacing
+// them with what they point to.  All Anchor fields (these are used to mark
+// anchor definitions) are cleared.
+func deAnchor(yn *yaml.Node) (res *yaml.Node, err error) {
+	if yn == nil {
+		return nil, nil
+	}
+	if yn.Anchor != "" {
+		// This node defines an anchor. Clear the field so that it
+		// doesn't show up when marshalling.
+		if yn.Kind == yaml.AliasNode {
+			// Maybe this is OK, but for now treating it as a bug.
+			return nil, fmt.Errorf(
+				"anchor %q defined using alias %v", yn.Anchor, yn.Alias)
+		}
+		yn.Anchor = ""
+	}
+	switch yn.Kind {
+	case yaml.ScalarNode:
+		return yn, nil
+	case yaml.AliasNode:
+		return deAnchor(yn.Alias)
+	case yaml.DocumentNode, yaml.MappingNode, yaml.SequenceNode:
+		for i := range yn.Content {
+			yn.Content[i], err = deAnchor(yn.Content[i])
+			if err != nil {
+				return nil, err
+			}
+		}
+		return yn, nil
+	default:
+		return nil, fmt.Errorf("cannot deAnchor kind %q", yn.Kind)
+	}
+}
+
 // GetValidatedMetadata returns metadata after subjecting it to some tests.
 func (rn *RNode) GetValidatedMetadata() (ResourceMeta, error) {
 	m, err := rn.GetMeta()

kyaml/yaml/rnode_test.go

@@ -696,6 +696,31 @@ spec:
 	}
 }
 
+func TestDeAnchor(t *testing.T) {
+	rn, err := Parse(`
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: wildcard
+data:
+  color: &color-used blue
+  feeling: *color-used
+`)
+	assert.NoError(t, err)
+	assert.NoError(t, rn.DeAnchor())
+	actual, err := rn.String()
+	assert.NoError(t, err)
+	assert.Equal(t, strings.TrimSpace(`
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: wildcard
+data:
+  color: blue
+  feeling: blue
+`), strings.TrimSpace(actual))
+}
+
 func TestRNode_UnmarshalJSON(t *testing.T) {
 	testCases := []struct {
 		testName string