Moves layer types to table

build.go

@@ -189,7 +189,7 @@ func Build(f BuildFunc, options ...Option) {
 	}
 
 	for _, layer := range result.Layers {
-		err = config.tomlWriter.Write(filepath.Join(layersPath, fmt.Sprintf("%s.toml", layer.Name)), layer)
+		err = config.tomlWriter.Write(filepath.Join(layersPath, fmt.Sprintf("%s.toml", layer.Name)), formattedLayer{layer, apiVersion})
 		if err != nil {
 			config.exitHandler.Error(err)
 			return

build_test.go

@@ -230,13 +230,60 @@ api = "0.4"
 		Expect(err).NotTo(HaveOccurred())
 
 		Expect(string(contents)).To(MatchTOML(`
+[types]
+  launch = true
+  build = true
+  cache = true
+
+[metadata]
+  some-key = "some-value"
+`))
+	})
+
+	context("when the buildpack api version is less than 0.6", func() {
+		it.Before(func() {
+			bpTOML := []byte(`
+api = "0.5"
+[buildpack]
+  id = "some-id"
+  name = "some-name"
+  version = "some-version"
+`)
+			Expect(os.WriteFile(filepath.Join(cnbDir, "buildpack.toml"), bpTOML, 0600)).To(Succeed())
+		})
+		it("persists layer metadata", func() {
+			packit.Build(func(ctx packit.BuildContext) (packit.BuildResult, error) {
+				layerPath := filepath.Join(ctx.Layers.Path, "some-layer")
+				Expect(os.MkdirAll(layerPath, os.ModePerm)).To(Succeed())
+
+				return packit.BuildResult{
+					Layers: []packit.Layer{
+						packit.Layer{
+							Path:   layerPath,
+							Name:   "some-layer",
+							Build:  true,
+							Launch: true,
+							Cache:  true,
+							Metadata: map[string]interface{}{
+								"some-key": "some-value",
+							},
+						},
+					},
+				}, nil
+			}, packit.WithArgs([]string{binaryPath, layersDir, platformDir, planPath}))
+
+			contents, err := os.ReadFile(filepath.Join(layersDir, "some-layer.toml"))
+			Expect(err).NotTo(HaveOccurred())
+
+			Expect(string(contents)).To(MatchTOML(`
 launch = true
 build = true
 cache = true
 
 [metadata]
   some-key = "some-value"
 `))
+		})
 	})
 
 	context("when there are existing layer.toml files", func() {

layer.go

@@ -3,55 +3,58 @@ package packit
 import (
 	"fmt"
 	"os"
+
+	"github.com/Masterminds/semver/v3"
+	"github.com/pelletier/go-toml"
 )
 
 // Layer provides a representation of a layer managed by a buildpack as
 // described by the specification:
 // https://github.com/buildpacks/spec/blob/main/buildpack.md#layers.
 type Layer struct {
 	// Path is the absolute location of the layer on disk.
-	Path string `toml:"-"`
+	Path string
 
 	// Name is the descriptive name of the layer.
-	Name string `toml:"-"`
+	Name string
 
 	// Build indicates whether the layer is available to subsequent buildpacks
 	// during their build phase according to the specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#build-layers.
-	Build bool `toml:"build"`
+	Build bool
 
 	// Launch indicates whether the layer is exported into the application image
 	// and made available during the launch phase according to the specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#launch-layers.
-	Launch bool `toml:"launch"`
+	Launch bool
 
 	// Cache indicates whether the layer is persisted and made available to
 	// subsequent builds of the same application according to the specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#launch-layers
 	// and
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#build-layers.
-	Cache bool `toml:"cache"`
+	Cache bool
 
 	// SharedEnv is the set of environment variables attached to the layer and
 	// made available during both the build and launch phases according to the
 	// specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#provided-by-the-buildpacks.
-	SharedEnv Environment `toml:"-"`
+	SharedEnv Environment
 
 	// BuildEnv is the set of environment variables attached to the layer and
 	// made available during the build phase according to the specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#provided-by-the-buildpacks.
-	BuildEnv Environment `toml:"-"`
+	BuildEnv Environment
 
 	// LaunchEnv is the set of environment variables attached to the layer and
 	// made available during the launch phase according to the specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#provided-by-the-buildpacks.
-	LaunchEnv Environment `toml:"-"`
+	LaunchEnv Environment
 
 	// ProcessLaunchEnv is a map of environment variables attached to the layer and
 	// made available to specified proccesses in the launch phase accoring to the specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#provided-by-the-buildpacks
-	ProcessLaunchEnv map[string]Environment `toml:"-"`
+	ProcessLaunchEnv map[string]Environment
 
 	// Metadata is an unspecified field allowing buildpacks to communicate extra
 	// details about the layer. Examples of this type of metadata might include
@@ -60,7 +63,7 @@ type Layer struct {
 	// layer if suitable. The Metadata field ultimately fills the metadata field
 	// of the Layer Content Metadata TOML file according to the specification:
 	// https://github.com/buildpacks/spec/blob/main/buildpack.md#layer-content-metadata-toml.
-	Metadata map[string]interface{} `toml:"metadata"`
+	Metadata map[string]interface{}
 }
 
 // Reset clears the state of a layer such that the layer can be replaced with
@@ -89,3 +92,29 @@ func (l Layer) Reset() (Layer, error) {
 
 	return l, nil
 }
+
+type formattedLayer struct {
+	layer Layer
+	api   *semver.Version
+}
+
+func (l formattedLayer) MarshalTOML() ([]byte, error) {
+	layer := map[string]interface{}{
+		"metadata": l.layer.Metadata,
+	}
+
+	apiV06, _ := semver.NewVersion("0.6")
+	if l.api.LessThan(apiV06) {
+		layer["build"] = l.layer.Build
+		layer["launch"] = l.layer.Launch
+		layer["cache"] = l.layer.Cache
+	} else {
+		layer["types"] = map[string]bool{
+			"build":  l.layer.Build,
+			"launch": l.layer.Launch,
+			"cache":  l.layer.Cache,
+		}
+	}
+
+	return toml.Marshal(layer)
+}