add new template function 'component' to kustomize controller

templates can use it to access the component which is triggering
the current reconcile/generate;
this function is in alpha state for now and might change in the future;

Author: cbarbian-sap

pkg/component/context.go

@@ -14,6 +14,7 @@ import (
 
 type reconcilerNameContextKey struct{}
 type clientContextKey struct{}
+type componentContextKey struct{}
 type componentDigestContextKey struct{}
 
 func newContext(ctx context.Context) *reconcileContext {
@@ -32,6 +33,10 @@ func (c *reconcileContext) WithClient(client cluster.Client) *reconcileContext {
 	return &reconcileContext{Context: context.WithValue(c, clientContextKey{}, client)}
 }
 
+func (c *reconcileContext) WithComponent(component Component) *reconcileContext {
+	return &reconcileContext{Context: context.WithValue(c, componentContextKey{}, component)}
+}
+
 func (c *reconcileContext) WithComponentDigest(componentDigest string) *reconcileContext {
 	return &reconcileContext{Context: context.WithValue(c, componentDigestContextKey{}, componentDigest)}
 }
@@ -50,6 +55,13 @@ func ClientFromContext(ctx context.Context) (cluster.Client, error) {
 	return nil, fmt.Errorf("client not found in context")
 }
 
+func ComponentFromContext(ctx context.Context) (Component, error) {
+	if component, ok := ctx.Value(componentContextKey{}).(Component); ok {
+		return component, nil
+	}
+	return nil, fmt.Errorf("component not found in context")
+}
+
 func ComponentDigestFromContext(ctx context.Context) (string, error) {
 	if componentDigest, ok := ctx.Value(componentDigestContextKey{}).(string); ok {
 		return componentDigest, nil

pkg/component/target.go

@@ -108,14 +108,10 @@ func (t *reconcileTarget[T]) Reconcile(ctx context.Context, component T) (bool,
 	componentDigest := calculateComponentDigest(component)
 
 	// render manifests
-	// TODO: sometimes the generator needs more information about the rendered component (such as the component's name or namespace);
-	// as of now, components have to help themselves through implementing post-read hooks; to simplify this for components,
-	// we could expose the component (full object or maybe just its metadata) via the generate context;
-	// another option would be to have a special NamespacedName reuse type, where the namespace part would be auto-defaulted
-	// by the framework (similar to the auto-loading of configmap/secret references)
 	generateCtx := newContext(ctx).
 		WithReconcilerName(t.reconcilerName).
 		WithClient(t.client).
+		WithComponent(component).
 		WithComponentDigest(componentDigest)
 	objects, err := t.resourceGenerator.Generate(generateCtx, namespace, name, component.GetSpec())
 	if err != nil {

pkg/manifests/kustomize/generator.go

@@ -12,6 +12,7 @@ import (
 	"io/fs"
 	"os"
 	"path/filepath"
+	"reflect"
 	"strings"
 	"text/template"
 
@@ -106,7 +107,7 @@ func NewKustomizeGenerator(fsys fs.FS, kustomizationPath string, templateSuffix
 					Funcs(templatex.FuncMapForTemplate(t)).
 					Funcs(templatex.FuncMapForLocalClient(client)).
 					Funcs(templatex.FuncMapForClient(nil)).
-					Funcs(funcMapForGenerateContext(nil, "", ""))
+					Funcs(funcMapForGenerateContext(nil, nil, "", ""))
 			} else {
 				t = t.New(name)
 			}
@@ -159,6 +160,10 @@ func (g *KustomizeGenerator) Generate(ctx context.Context, namespace string, nam
 	if err != nil {
 		return nil, err
 	}
+	component, err := component.ComponentFromContext(ctx)
+	if err != nil {
+		return nil, err
+	}
 
 	data := parameters.ToUnstructured()
 	fsys := kustfsys.MakeFsInMemory()
@@ -178,7 +183,7 @@ func (g *KustomizeGenerator) Generate(ctx context.Context, namespace string, nam
 			}
 			t0.Option("missingkey=zero").
 				Funcs(templatex.FuncMapForClient(client)).
-				Funcs(funcMapForGenerateContext(client, namespace, name))
+				Funcs(funcMapForGenerateContext(client, component, namespace, name))
 		}
 		var buf bytes.Buffer
 		if err := t0.ExecuteTemplate(&buf, t.Name(), data); err != nil {
@@ -234,14 +239,28 @@ func (g *KustomizeGenerator) Generate(ctx context.Context, namespace string, nam
 	return objects, nil
 }
 
-func funcMapForGenerateContext(client cluster.Client, namespace string, name string) template.FuncMap {
+func funcMapForGenerateContext(client cluster.Client, component component.Component, namespace string, name string) template.FuncMap {
 	// TODO: add accessors for Kubernetes version etc.
 	return template.FuncMap{
+		// TODO: maybe it would it be better to convert component to unstructured;
+		// then calling methods would no longer be possible, and attributes would be in lowercase
+		"component": makeFuncData(component),
 		"namespace": func() string { return namespace },
 		"name":      func() string { return name },
 	}
 }
 
+func makeFuncData(data any) any {
+	if data == nil {
+		return func() any { return nil }
+	}
+	ival := reflect.ValueOf(data)
+	ityp := ival.Type()
+	ftyp := reflect.FuncOf(nil, []reflect.Type{ityp}, false)
+	fval := reflect.MakeFunc(ftyp, func(args []reflect.Value) []reflect.Value { return []reflect.Value{ival} })
+	return fval.Interface()
+}
+
 func generateKustomization(fsys kustfsys.FileSystem) ([]byte, error) {
 	var resources []string