feat: source-defined buildpacks (#1774)

Allows buildpacks to be updated by updating to a newer version of
func.  Previously, buildpacs were fixed at time of function creation
without a manual edit of func.yaml.  Currently using Go as the reference
implementation in this commit.

pkg/builders/buildpacks/builder.go

@@ -44,6 +44,10 @@ var (
 		"ghcr.io/vmware-tanzu/function-buildpacks-for-knative/",
 		"gcr.io/buildpacks/",
 	}
+
+	defaultBuildpacks = map[string][]string{
+		"go": {"paketo-buildpacks/go-dist", "ghcr.io/boson-project/go-function-buildpack:tip"},
+	}
 )
 
 // Builder will build Function using Pack.
@@ -115,13 +119,18 @@ func (b *Builder) Build(ctx context.Context, f fn.Function) (err error) {
 		return
 	}
 
+	buildpacks := f.Build.Buildpacks
+	if len(buildpacks) == 0 {
+		buildpacks = defaultBuildpacks[f.Runtime]
+	}
+
 	// Pack build options
 	opts := pack.BuildOptions{
 		AppPath:        f.Root,
 		Image:          f.Image,
 		LifecycleImage: DefaultLifecycleImage,
 		Builder:        image,
-		Buildpacks:     f.Build.Buildpacks,
+		Buildpacks:     buildpacks,
 		ContainerConfig: struct {
 			Network string
 			Volumes []string

pkg/builders/buildpacks/builder_test.go

@@ -2,6 +2,7 @@ package buildpacks
 
 import (
 	"context"
+	"reflect"
 	"testing"
 
 	pack "github.com/buildpacks/pack/pkg/client"
@@ -9,9 +10,9 @@ import (
 	fn "knative.dev/func/pkg/functions"
 )
 
-// Test_BuilderImageUntrusted ensures that only known builder images
+// TestBuild_BuilderImageUntrusted ensures that only known builder images
 // are to be considered trusted.
-func Test_BuilderImageUntrusted(t *testing.T) {
+func TestBuild_BuilderImageUntrusted(t *testing.T) {
 	var untrusted = []string{
 		// Check prefixes that end in a slash
 		"quay.io/bosonhack/",
@@ -28,9 +29,9 @@ func Test_BuilderImageUntrusted(t *testing.T) {
 	}
 }
 
-// Test_BuilderImageTrusted ensures that only known builder images
+// TestBuild_BuilderImageTrusted ensures that only known builder images
 // are to be considered trusted.
-func Test_BuilderImageTrusted(t *testing.T) {
+func TestBuild_BuilderImageTrusted(t *testing.T) {
 	for _, builder := range trustedBuilderImagePrefixes {
 		if !TrustBuilder(builder) {
 			t.Fatalf("expected pack builder image %v to be trusted", builder)
@@ -38,9 +39,9 @@ func Test_BuilderImageTrusted(t *testing.T) {
 	}
 }
 
-// Test_BuilderImageDefault ensures that a Function bing built which does not
+// TestBuild_BuilderImageDefault ensures that a Function bing built which does not
 // define a Builder Image will get the internally-defined default.
-func Test_BuilderImageDefault(t *testing.T) {
+func TestBuild_BuilderImageDefault(t *testing.T) {
 	var (
 		i = &mockImpl{}
 		b = NewBuilder(WithImpl(i))
@@ -61,9 +62,33 @@ func Test_BuilderImageDefault(t *testing.T) {
 
 }
 
-// Test_BuilderImageConfigurable ensures that the builder will use the builder
+// TestBuild_BuildpacksDefault ensures that, if there are default buildpacks
+// defined in-code, but none defined on the function, the defaults will be
+// used.
+func TestBuild_BuildpacksDefault(t *testing.T) {
+	var (
+		i = &mockImpl{}
+		b = NewBuilder(WithImpl(i))
+		f = fn.Function{Runtime: "go"}
+	)
+
+	i.BuildFn = func(ctx context.Context, opts pack.BuildOptions) error {
+		expected := defaultBuildpacks["go"]
+		if !reflect.DeepEqual(expected, opts.Buildpacks) {
+			t.Fatalf("expected buildpacks '%v', got '%v'", expected, opts.Buildpacks)
+		}
+		return nil
+	}
+
+	if err := b.Build(context.Background(), f); err != nil {
+		t.Fatal(err)
+	}
+
+}
+
+// TestBuild_BuilderImageConfigurable ensures that the builder will use the builder
 // image defined on the given Function if provided.
-func Test_BuilderImageConfigurable(t *testing.T) {
+func TestBuild_BuilderImageConfigurable(t *testing.T) {
 	var (
 		i = &mockImpl{} // mock underlying implementation
 		b = NewBuilder( // Func Builder logic
@@ -91,9 +116,9 @@ func Test_BuilderImageConfigurable(t *testing.T) {
 	}
 }
 
-// Test_BuildEnvs ensures that build environment variables are interpolated and
+// TestBuild_Envs ensures that build environment variables are interpolated and
 // provided in Build Options
-func Test_BuildEnvs(t *testing.T) {
+func TestBuild_Envs(t *testing.T) {
 	t.Setenv("INTERPOLATE_ME", "interpolated")
 	var (
 		envName  = "NAME"
@@ -123,7 +148,8 @@ func Test_BuildEnvs(t *testing.T) {
 	}
 }
 
-func Test_BuildErrors(t *testing.T) {
+// TestBuild_Errors confirms error scenarios.
+func TestBuild_Errors(t *testing.T) {
 	testCases := []struct {
 		name, runtime, expectedErr string
 	}{

templates/go/manifest.yaml

@@ -1,5 +0,0 @@
-# Optional list of additional Buildpacks to be applied to the language pack's
-# builder image when the Function is built using a Buildpack builder.
-buildpacks:
-  - paketo-buildpacks/go-dist
-  - ghcr.io/boson-project/go-function-buildpack:tip