Honor ks.spec.postBuild.substituteStrategy

Signed-off-by: Matheus Pimenta <matheuscscp@gmail.com>

internal/build/build.go

@@ -620,6 +620,7 @@ func (b *Builder) do(ctx context.Context, kustomization kustomizev1.Kustomizatio
 			res,
 			kustomize.SubstituteWithDryRun(b.dryRun),
 			kustomize.SubstituteWithStrict(b.strictSubst),
+			kustomize.SubstituteWithAlways(kustomization.GetSubstituteStrategy() == kustomizev1.SubstituteStrategyAlways),
 		)
 		if err != nil {
 			return nil, fmt.Errorf("var substitution failed for '%s': %w", res.GetName(), err)

internal/build/build_test.go

@@ -875,3 +875,58 @@ func Test_Build_preserveAllLabels(t *testing.T) {
 		t.Errorf("expected owner namespace label \"flux-system\", got %v", got)
 	}
 }
+
+func Test_Build_substituteStrategy(t *testing.T) {
+	tests := []struct {
+		name      string
+		ksFile    string
+		wantColor string
+		wantShape string
+	}{
+		{
+			// The default WithVariables strategy skips substitution when no
+			// variables are defined, leaving the defaulted expressions untouched.
+			name:      "WithVariables skips substitution without variables",
+			ksFile:    "testdata/substitute-strategy/with-variables.yaml",
+			wantColor: "${color:=blue}",
+			wantShape: "${shape:=square}",
+		},
+		{
+			// The Always strategy performs substitution even without variables,
+			// resolving the expressions to their defaults.
+			name:      "Always substitutes defaults without variables",
+			ksFile:    "testdata/substitute-strategy/always.yaml",
+			wantColor: "blue",
+			wantShape: "square",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			b, err := NewBuilder("test-ks", "testdata/substitute-strategy/resources",
+				WithDryRun(true),
+				WithNamespace("flux-system"),
+				WithKustomizationFile(tt.ksFile),
+			)
+			if err != nil {
+				t.Fatalf("unable to create builder: %v", err)
+			}
+
+			objects, err := b.Build()
+			if err != nil {
+				t.Fatalf("build failed: %v", err)
+			}
+			if len(objects) == 0 {
+				t.Fatal("expected at least one object, got none")
+			}
+
+			data, _, _ := unstructured.NestedStringMap(objects[0].Object, "data")
+			if got := data["color"]; got != tt.wantColor {
+				t.Errorf("expected color=%q, got %q", tt.wantColor, got)
+			}
+			if got := data["shape"]; got != tt.wantShape {
+				t.Errorf("expected shape=%q, got %q", tt.wantShape, got)
+			}
+		})
+	}
+}

internal/build/testdata/substitute-strategy/always.yaml

@@ -0,0 +1,9 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: test-ks
+  namespace: flux-system
+spec:
+  path: "./resources"
+  postBuild:
+    substituteStrategy: Always

internal/build/testdata/substitute-strategy/resources/configmap.yaml

@@ -0,0 +1,7 @@
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: test-config
+data:
+  color: "${color:=blue}"
+  shape: "${shape:=square}"

internal/build/testdata/substitute-strategy/resources/kustomization.yaml

@@ -0,0 +1,4 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - configmap.yaml

internal/build/testdata/substitute-strategy/with-variables.yaml

@@ -0,0 +1,8 @@
+apiVersion: kustomize.toolkit.fluxcd.io/v1
+kind: Kustomization
+metadata:
+  name: test-ks
+  namespace: flux-system
+spec:
+  path: "./resources"
+  postBuild: {}