Use OpenAPI when merging (3way) resources

- When merging (3way) resources use the patch strategy from the openAPI if the definition exists for the field
- Allow disabling of guessing patch strategy merge keys when no definition exists
- Support defining strategy and key directly on configuration fields through line and header coments
- Support attaching schema to parent fields of lists, and propagating -- e.g. that a field is a PodTemplate

kyaml/yaml/walk/walk.go

@@ -8,20 +8,30 @@ import (
 	"os"
 	"strings"
 
+	"sigs.k8s.io/kustomize/kyaml/fieldmeta"
+	"sigs.k8s.io/kustomize/kyaml/openapi"
 	"sigs.k8s.io/kustomize/kyaml/yaml"
+	"sigs.k8s.io/kustomize/kyaml/yaml/schema"
 )
 
-// Filter walks the Source RNode and modifies the RNode provided to GrepFilter.
+// Walker walks the Source RNode and modifies the RNode provided to GrepFilter.
 type Walker struct {
 	// Visitor is invoked by GrepFilter
 	Visitor
 
+	Schema *openapi.ResourceSchema
+
 	// Source is the RNode to walk.  All Source fields and associative list elements
 	// will be visited.
 	Sources Sources
 
 	// Path is the field path to the current Source Node.
 	Path []string
+
+	// InferAssociativeLists if set to true will infer merge strategies for
+	// fields which it doesn't have the schema based on the fields in the
+	// list elements.
+	InferAssociativeLists bool
 }
 
 func (l Walker) Kind() yaml.Kind {
@@ -35,6 +45,8 @@ func (l Walker) Kind() yaml.Kind {
 
 // GrepFilter implements yaml.GrepFilter
 func (l Walker) Walk() (*yaml.RNode, error) {
+	l.Schema = l.GetSchema()
+
 	// invoke the handler for the corresponding node type
 	switch l.Kind() {
 	case yaml.MappingNode:
@@ -46,7 +58,7 @@ func (l Walker) Walk() (*yaml.RNode, error) {
 		if err := yaml.ErrorIfAnyInvalidAndNonNull(yaml.SequenceNode, l.Sources...); err != nil {
 			return nil, err
 		}
-		if yaml.IsAssociative(l.Sources) {
+		if schema.IsAssociative(l.Schema, l.Sources, l.InferAssociativeLists) {
 			return l.walkAssociativeSequence()
 		}
 		return l.walkNonAssociativeSequence()
@@ -64,6 +76,49 @@ func (l Walker) Walk() (*yaml.RNode, error) {
 	}
 }
 
+func (l Walker) GetSchema() *openapi.ResourceSchema {
+	for i := range l.Sources {
+		r := l.Sources[i]
+		if yaml.IsEmpty(r) {
+			continue
+		}
+
+		fm := fieldmeta.FieldMeta{}
+		if err := fm.Read(r); err == nil && !fm.IsEmpty() {
+			// per-field schema, this is fine
+			if fm.Schema.Ref.String() != "" {
+				// resolve the reference
+				s, err := openapi.Resolve(&fm.Schema.Ref)
+				if err == nil && s != nil {
+					fm.Schema = *s
+				}
+			}
+			return &openapi.ResourceSchema{Schema: &fm.Schema}
+		}
+	}
+
+	if l.Schema != nil {
+		return l.Schema
+	}
+	for i := range l.Sources {
+		r := l.Sources[i]
+		if yaml.IsEmpty(r) {
+			continue
+		}
+
+		m, _ := r.GetMeta()
+		if m.Kind == "" || m.APIVersion == "" {
+			continue
+		}
+
+		s := openapi.SchemaForResourceType(yaml.TypeMeta{Kind: m.Kind, APIVersion: m.APIVersion})
+		if s != nil {
+			return s
+		}
+	}
+	return nil
+}
+
 const (
 	DestIndex = iota
 	OriginIndex