Introduce resmap.ApplyFilter.

api/resmap/resmap.go

@@ -9,6 +9,7 @@ import (
 	"sigs.k8s.io/kustomize/api/ifc"
 	"sigs.k8s.io/kustomize/api/resource"
 	"sigs.k8s.io/kustomize/api/types"
+	"sigs.k8s.io/kustomize/kyaml/kio"
 	"sigs.k8s.io/kustomize/kyaml/resid"
 	"sigs.k8s.io/kustomize/kyaml/yaml"
 )
@@ -173,7 +174,7 @@ type ResMap interface {
 	// in the resid.DefaultNamespace entry.
 	GroupedByCurrentNamespace() map[string][]*resource.Resource
 
-	// GroupByOrginalNamespace performs as GroupByNamespace
+	// GroupedByOriginalNamespace performs as GroupByNamespace
 	// but use the original namespace instead of the current
 	// one to perform the grouping.
 	GroupedByOriginalNamespace() map[string][]*resource.Resource
@@ -253,4 +254,14 @@ type ResMap interface {
 
 	// RemoveBuildAnnotations removes annotations created by the build process.
 	RemoveBuildAnnotations()
+
+	// ApplyFilter applies an RNode filter to all Resources in the ResMap.
+	// TODO: Send/recover ancillary Resource data to/from subprocesses.
+	// Assure that the ancillary data in Resource (everything not in the RNode)
+	// is sent to and re-captured from transformer subprocess (as the process
+	// might edit that information).  One way to do this would be to solely use
+	// RNode metadata annotation reading and writing instead of using Resource
+	// struct data members, i.e. the Resource struct is replaced by RNode
+	// and use of (slow) k8s metadata annotations inside the RNode.
+	ApplyFilter(f kio.Filter) error
 }

api/resmap/reswrangler.go

@@ -10,6 +10,7 @@ import (
 	"github.com/pkg/errors"
 	"sigs.k8s.io/kustomize/api/resource"
 	"sigs.k8s.io/kustomize/api/types"
+	"sigs.k8s.io/kustomize/kyaml/kio"
 	"sigs.k8s.io/kustomize/kyaml/resid"
 	kyaml "sigs.k8s.io/kustomize/kyaml/yaml"
 )
@@ -423,6 +424,7 @@ func getNamespacesForRoleBinding(r *resource.Resource) map[string]bool {
 	if r.GetKind() != "RoleBinding" {
 		return result
 	}
+	//nolint staticcheck
 	subjects, err := r.GetSlice("subjects")
 	if err != nil || subjects == nil {
 		return result
@@ -617,3 +619,41 @@ func (m *resWrangler) RemoveBuildAnnotations() {
 		r.RemoveBuildAnnotations()
 	}
 }
+
+// ApplyFilter implements ResMap.
+func (m *resWrangler) ApplyFilter(f kio.Filter) error {
+	reverseLookup := make(map[*kyaml.RNode]*resource.Resource, len(m.rList))
+	nodes := make([]*kyaml.RNode, len(m.rList))
+	for i, r := range m.rList {
+		ptr := r.Node()
+		nodes[i] = ptr
+		reverseLookup[ptr] = r
+	}
+	// The filter can modify nodes, but also delete and create them.
+	// The filtered list might be smaller or larger than the nodes list.
+	filtered, err := f.Filter(nodes)
+	if err != nil {
+		return err
+	}
+	// Rebuild the resmap from the filtered RNodes.
+	var nRList []*resource.Resource
+	for _, rn := range filtered {
+		if rn.IsNilOrEmpty() {
+			// A node might make it through the filter as an object,
+			// but still be empty.  Drop such entries.
+			continue
+		}
+		res, ok := reverseLookup[rn]
+		if !ok {
+			// A node was created; make a Resource to wrap it.
+			// Leave remaining Resource fields empty.
+			// At time of writing, seeking to eliminate those fields.
+			// Alternatively, could just return error on creation attempt
+			// until remaining fields eliminated.
+			res = resource.NewResource(rn)
+		}
+		nRList = append(nRList, res)
+	}
+	m.rList = nRList
+	return nil
+}

api/resmap/reswrangler_test.go

@@ -11,12 +11,16 @@ import (
 	"testing"
 
 	"github.com/stretchr/testify/assert"
+	"sigs.k8s.io/kustomize/api/filters/labels"
 	"sigs.k8s.io/kustomize/api/provider"
 	. "sigs.k8s.io/kustomize/api/resmap"
 	"sigs.k8s.io/kustomize/api/resource"
+	kusttest_test "sigs.k8s.io/kustomize/api/testutils/kusttest"
 	resmaptest_test "sigs.k8s.io/kustomize/api/testutils/resmaptest"
 	"sigs.k8s.io/kustomize/api/types"
+	"sigs.k8s.io/kustomize/kyaml/kio"
 	"sigs.k8s.io/kustomize/kyaml/resid"
+	"sigs.k8s.io/kustomize/kyaml/yaml"
 )
 
 var depProvider = provider.NewDefaultDepProvider()
@@ -1144,6 +1148,186 @@ func addNamespace(namespace string, base string) string {
 	return res
 }
 
+// DeleteOddsFilter deletes the odd entries, removing nodes.
+// This is a ridiculous filter for testing.
+type DeleteOddsFilter struct{}
+
+func (f DeleteOddsFilter) Filter(
+	nodes []*yaml.RNode) (result []*yaml.RNode, err error) {
+	for i := range nodes {
+		if i%2 == 0 {
+			// Keep the even entries, drop the odd entries.
+			result = append(result, nodes[i])
+		}
+	}
+	return
+}
+
+// CloneOddsFilter deletes even entries and clones odd entries,
+// making new nodes.
+// This is a ridiculous filter for testing.
+type CloneOddsFilter struct{}
+
+func (f CloneOddsFilter) Filter(
+	nodes []*yaml.RNode) (result []*yaml.RNode, err error) {
+	for i := range nodes {
+		if i%2 != 0 {
+			newNode := nodes[i].Copy()
+			// Add suffix to the name, so that it's unique (w/r to this test).
+			newNode.SetName(newNode.GetName() + "Clone")
+			// Return a ptr to the copy.
+			result = append(result, nodes[i], newNode)
+		}
+	}
+	return
+}
+
+func TestApplyFilter(t *testing.T) {
+	tests := map[string]struct {
+		input    string
+		f        kio.Filter
+		expected string
+	}{
+		"labels": {
+			input: `
+apiVersion: example.com/v1
+kind: Beans
+metadata:
+  name: myBeans
+---
+apiVersion: example.com/v1
+kind: Franks
+metadata:
+  name: myFranks
+`,
+			f: labels.Filter{
+				Labels: map[string]string{
+					"a": "foo",
+					"b": "bar",
+				},
+				FsSlice: types.FsSlice{
+					{
+						Gvk:                resid.NewGvk("example.com", "v1", "Beans"),
+						Path:               "metadata/labels",
+						CreateIfNotPresent: true,
+					},
+				},
+			},
+			expected: `
+apiVersion: example.com/v1
+kind: Beans
+metadata:
+  labels:
+    a: foo
+    b: bar
+  name: myBeans
+---
+apiVersion: example.com/v1
+kind: Franks
+metadata:
+  name: myFranks
+`,
+		},
+		"deleteOddNodes": {
+			input: `
+apiVersion: example.com/v1
+kind: Zero
+metadata:
+  name: r0
+---
+apiVersion: example.com/v1
+kind: One
+metadata:
+  name: r1
+---
+apiVersion: example.com/v1
+kind: Two
+metadata:
+  name: r2
+---
+apiVersion: example.com/v1
+kind: Three
+metadata:
+  name: r3
+`,
+			f: DeleteOddsFilter{},
+			expected: `
+apiVersion: example.com/v1
+kind: Zero
+metadata:
+  name: r0
+---
+apiVersion: example.com/v1
+kind: Two
+metadata:
+  name: r2
+`,
+		},
+		"cloneOddNodes": {
+			// input list has five entries
+			input: `
+apiVersion: example.com/v1
+kind: Zero
+metadata:
+  name: r0
+---
+apiVersion: example.com/v1
+kind: One
+metadata:
+  name: r1
+---
+apiVersion: example.com/v1
+kind: Two
+metadata:
+  name: r2
+---
+apiVersion: example.com/v1
+kind: Three
+metadata:
+  name: r3
+---
+apiVersion: example.com/v1
+kind: Four
+metadata:
+  name: r4
+`,
+			f: CloneOddsFilter{},
+			// output has four, but half are newly created nodes.
+			expected: `
+apiVersion: example.com/v1
+kind: One
+metadata:
+  name: r1
+---
+apiVersion: example.com/v1
+kind: One
+metadata:
+  name: r1Clone
+---
+apiVersion: example.com/v1
+kind: Three
+metadata:
+  name: r3
+---
+apiVersion: example.com/v1
+kind: Three
+metadata:
+  name: r3Clone
+`,
+		},
+	}
+	for name := range tests {
+		tc := tests[name]
+		t.Run(name, func(t *testing.T) {
+			m, err := rmF.NewResMapFromBytes([]byte(tc.input))
+			assert.NoError(t, err)
+			assert.NoError(t, m.ApplyFilter(tc.f))
+			kusttest_test.AssertActualEqualsExpectedWithTweak(
+				t, m, nil, tc.expected)
+		})
+	}
+}
+
 func TestApplySmPatch_Deletion(t *testing.T) {
 	target := `
 apiVersion: apps/v1