PoC to add Components to a separate components list (instead of resources)

If this idea is preferred, the code could really do with a refactor (probably using closures to control the behaviour of accumulate directory)

api/internal/target/kusttarget.go

@@ -164,6 +164,10 @@ func (kt *KustTarget) accumulateTarget(ra *accumulator.ResAccumulator) (
 	if err != nil {
 		return nil, errors.Wrap(err, "accumulating resources")
 	}
+	ra, err = kt.accumulateComponents(ra, kt.kustomization.Components)
+	if err != nil {
+		return nil, errors.Wrap(err, "accumulating components")
+	}
 	tConfig, err := builtinconfig.MakeTransformerConfig(
 		kt.ldr, kt.kustomization.Configurations)
 	if err != nil {
@@ -273,7 +277,7 @@ func (kt *KustTarget) accumulateResources(
 				return nil, fmt.Errorf("accumulateFile %q, loader.New %q", errF, errL)
 			}
 			var errD error
-			ra, errD = kt.accumulateDirectory(ra, ldr)
+			ra, errD = kt.accumulateDirectory(ra, ldr, false)
 			if errD != nil {
 				return nil, fmt.Errorf("accumulateFile %q, accumulateDirector: %q", errF, errD)
 			}
@@ -282,8 +286,27 @@ func (kt *KustTarget) accumulateResources(
 	return ra, nil
 }
 
+// accumulateResources fills the given resourceAccumulator
+// with resources read from the given list of paths.
+func (kt *KustTarget) accumulateComponents(
+	ra *accumulator.ResAccumulator, paths []string) (*accumulator.ResAccumulator, error) {
+	for _, path := range paths {
+		// Components always refer to directories
+		ldr, errL := kt.ldr.New(path)
+		if errL != nil {
+			return nil, fmt.Errorf("loader.New %q", errL)
+		}
+		var errD error
+		ra, errD = kt.accumulateDirectory(ra, ldr, true)
+		if errD != nil {
+			return nil, fmt.Errorf("accumulateDirectory: %q", errD)
+		}
+	}
+	return ra, nil
+}
+
 func (kt *KustTarget) accumulateDirectory(
-	ra *accumulator.ResAccumulator, ldr ifc.Loader) (*accumulator.ResAccumulator, error) {
+	ra *accumulator.ResAccumulator, ldr ifc.Loader, isComponent bool) (*accumulator.ResAccumulator, error) {
 	defer ldr.Cleanup()
 	subKt := NewKustTarget(
 		ldr, kt.validator, kt.rFactory, kt.tFactory, kt.pLdr)
@@ -292,6 +315,13 @@ func (kt *KustTarget) accumulateDirectory(
 		return nil, errors.Wrapf(
 			err, "couldn't make target for path '%s'", ldr.Root())
 	}
+	if isComponent && subKt.kustomization.Kind != types.ComponentKind {
+		return nil, fmt.Errorf(
+			"expected kind '%s' for path '%s' but got '%s'", types.ComponentKind, ldr.Root(), subKt.kustomization.Kind)
+	} else if !isComponent && subKt.kustomization.Kind == types.ComponentKind {
+		return nil, fmt.Errorf(
+			"expected kind != '%s' for path '%s'", types.ComponentKind, ldr.Root())
+	}
 
 	var subRa *accumulator.ResAccumulator
 	if subKt.kustomization.Kind == types.ComponentKind {

api/krusty/component_test.go

@@ -62,8 +62,10 @@ func writeComponentProd(th kusttest_test.Harness) {
 	th.WriteK("/app/prod", `
 resources:
 - ../base
-- ../patch
 - db
+
+components:
+- ../patch
 `)
 	th.WriteF("/app/prod/db", `
 apiVersion: v1
@@ -105,16 +107,16 @@ metadata:
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: patched-stub
+  name: patched-db
 spec:
-  replicas: 1
+  type: Logical
 ---
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: db
+  name: patched-stub
 spec:
-  type: Logical
+  replicas: 1
 `)
 }
 
@@ -135,9 +137,11 @@ configMapGenerator:
 	th.WriteK("/app/prod", `
 resources:
 - ../base
+- db
+
+components:
 - ../patch
 - ../additionalpatch
-- db
 `)
 	m := th.Run("/app/prod", th.MakeDefaultOptions())
 	th.AssertActualEqualsExpected(m, `
@@ -162,16 +166,16 @@ metadata:
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: patched-stub
+  name: patched-db
 spec:
-  replicas: 1
+  type: Logical
 ---
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: db
+  name: patched-stub
 spec:
-  type: Logical
+  replicas: 1
 `)
 }
 
@@ -183,7 +187,7 @@ func TestNestedComponents(t *testing.T) {
 	th.WriteF("/app/additionalpatch/kustomization.yaml", `
 apiVersion: kustomize.config.k8s.io/v1alpha1
 kind: Component
-resources:
+components:
 - ../patch
 configMapGenerator:
 - name: my-configmap
@@ -194,8 +198,10 @@ configMapGenerator:
 	th.WriteK("/app/prod", `
 resources:
 - ../base
-- ../additionalpatch
 - db
+
+components:
+- ../additionalpatch
 `)
 	m := th.Run("/app/prod", th.MakeDefaultOptions())
 	th.AssertActualEqualsExpected(m, `
@@ -220,16 +226,16 @@ metadata:
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: patched-stub
+  name: patched-db
 spec:
-  replicas: 1
+  type: Logical
 ---
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: db
+  name: patched-stub
 spec:
-  type: Logical
+  replicas: 1
 `)
 }
 
@@ -283,16 +289,16 @@ metadata:
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: patched-stub
+  name: patched-db
 spec:
-  replicas: 1
+  type: Logical
 ---
 apiVersion: v1
 kind: Deployment
 metadata:
-  name: db
+  name: patched-stub
 spec:
-  type: Logical
+  replicas: 1
 `)
 }
 
@@ -334,6 +340,44 @@ metadata:
 `)
 }
 
+func TestComponentsCannotBeAddedToResources(t *testing.T) {
+	th := kusttest_test.MakeHarness(t)
+	writeComponentBase(th)
+	writeComponentPatch(th)
+	th.WriteF("/app/custinres/kustomization.yaml", `
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+- ../base
+- ../patch
+`)
+	err := th.RunWithErr("/app/custinres", th.MakeDefaultOptions())
+	if !strings.Contains(
+		err.Error(),
+		"expected kind != 'Component' for path '/app/patch'") {
+		t.Fatalf("unexpected error: %s", err)
+	}
+}
+
+func TestResourcesCannotBeAddedToComponents(t *testing.T) {
+	th := kusttest_test.MakeHarness(t)
+	writeComponentBase(th)
+	writeComponentPatch(th)
+	th.WriteF("/app/resincust/kustomization.yaml", `
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+components:
+- ../base
+- ../patch
+`)
+	err := th.RunWithErr("/app/resincust", th.MakeDefaultOptions())
+	if !strings.Contains(
+		err.Error(),
+		"accumulating components: accumulateDirectory: \"expected kind 'Component' for path '/app/base' but got 'Kustomization'") {
+		t.Fatalf("unexpected error: %s", err)
+	}
+}
+
 func TestMissingOptionalComponentApiVersion(t *testing.T) {
 	th := kusttest_test.MakeHarness(t)
 	writeComponentBase(th)

api/types/kustomization.go

@@ -75,10 +75,14 @@ type Kustomization struct {
 	//
 
 	// Resources specifies relative paths to files holding YAML representations
-	// of kubernetes API objects, or specifcations of other kustomizations
+	// of kubernetes API objects, or specifications of other kustomizations
 	// via relative paths, absolute paths, or URLs.
 	Resources []string `json:"resources,omitempty" yaml:"resources,omitempty"`
 
+	// Components specifies relative paths to specifications of other Components
+	// via relative paths, absolute paths, or URLs.
+	Components []string `json:"components,omitempty" yaml:"components,omitempty"`
+
 	// Crds specifies relative paths to Custom Resource Definition files.
 	// This allows custom resources to be recognized as operands, making
 	// it possible to add them to the Resources list.