Introduce ValidHoldingNode

... for algorithms that are only applicable to Nodes that hold exactly
one value: documents, array items, and map items.

pkg/schema/schema.go

@@ -70,7 +70,7 @@ func NewNullSchema() *DocumentSchema {
 }
 
 func NewDocumentType(doc *yamlmeta.Document) (*DocumentType, error) {
-	typeOfValue, err := getTypeFromValueHoldingNode(doc)
+	typeOfValue, err := getType(doc)
 	if err != nil {
 		return nil, err
 	}
@@ -93,7 +93,7 @@ func NewMapType(m *yamlmeta.Map) (*MapType, error) {
 }
 
 func NewMapItemType(item *yamlmeta.MapItem) (*MapItemType, error) {
-	typeOfValue, err := getTypeFromValueHoldingNode(item)
+	typeOfValue, err := getType(item)
 	if err != nil {
 		return nil, err
 	}
@@ -120,17 +120,15 @@ func NewArrayType(a *yamlmeta.Array) (*ArrayType, error) {
 }
 
 func NewArrayItemType(item *yamlmeta.ArrayItem) (*ArrayItemType, error) {
-	typeOfValue, err := getTypeFromValueHoldingNode(item)
+	typeOfValue, err := getType(item)
 	if err != nil {
 		return nil, err
 	}
 
 	return &ArrayItemType{ValueType: typeOfValue, defaultValue: typeOfValue.GetDefaultValue(), Position: item.GetPosition()}, nil
 }
 
-// getTypeFromValueHoldingNode derives the yamlmeta.Type from the given `node`.
-//    a "value-holding node" is a node that holds an actual value: Document, ArrayItem, or MapItem
-func getTypeFromValueHoldingNode(node yamlmeta.Node) (yamlmeta.Type, error) {
+func getType(node yamlmeta.ValueHoldingNode) (yamlmeta.Type, error) {
 	var typeOfValue yamlmeta.Type
 
 	anns, err := collectAnnotations(node)
@@ -140,13 +138,13 @@ func getTypeFromValueHoldingNode(node yamlmeta.Node) (yamlmeta.Type, error) {
 	typeOfValue = getTypeFromAnnotations(anns)
 
 	if typeOfValue == nil {
-		typeOfValue, err = inferTypeFromValue(node.GetValues()[0], node.GetPosition())
+		typeOfValue, err = inferTypeFromValue(node.Val(), node.GetPosition())
 		if err != nil {
 			return nil, err
 		}
 	}
 
-	err = valueTypeAllowsItemValue(typeOfValue, node.GetValues()[0], node.GetPosition())
+	err = valueTypeAllowsItemValue(typeOfValue, node.Val(), node.GetPosition())
 	if err != nil {
 		return nil, err
 	}

pkg/yamlmeta/ast.go

@@ -30,8 +30,13 @@ type Node interface {
 	sealed() // limit the concrete types of Node to map directly only to types allowed in YAML spec.
 }
 
-// Ensure: all types are — in fact — assignable to Node
-var _ = []Node{&DocumentSet{}, &Document{}, &Map{}, &MapItem{}, &Array{}, &ArrayItem{}}
+type ValueHoldingNode interface {
+	Node
+	Val() interface{}
+}
+
+var _ = []Node{&DocumentSet{}, &Map{}, &Array{}}
+var _ = []ValueHoldingNode{&Document{}, &MapItem{}, &ArrayItem{}}
 
 type DocumentSet struct {
 	Metas    []*Meta

pkg/yamlmeta/value_holding_node.go

@@ -0,0 +1,14 @@
+// Copyright 2020 VMware, Inc.
+// SPDX-License-Identifier: Apache-2.0
+
+package yamlmeta
+
+func (d *Document) Val() interface{} {
+	return d.Value
+}
+func (mi *MapItem) Val() interface{} {
+	return mi.Value
+}
+func (ai *ArrayItem) Val() interface{} {
+	return ai.Value
+}