Adds support for setting default process

build.go

@@ -1,6 +1,7 @@
 package packit
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"path/filepath"
@@ -131,6 +132,7 @@ func Build(f BuildFunc, options ...Option) {
 	}
 
 	apiV05, _ := semver.NewVersion("0.5")
+	apiV06, _ := semver.NewVersion("0.6")
 	apiVersion, err := semver.NewVersion(buildpackInfo.APIVersion)
 	if err != nil {
 		config.exitHandler.Error(err)
@@ -157,7 +159,7 @@ func Build(f BuildFunc, options ...Option) {
 
 	if len(result.Plan.Entries) > 0 {
 		if apiVersion.GreaterThan(apiV05) || apiVersion.Equal(apiV05) {
-			config.exitHandler.Error(fmt.Errorf(`buildpack plan is read only since BuildPack API v0.5`))
+			config.exitHandler.Error(errors.New("buildpack plan is read only since Buildpack API v0.5"))
 			return
 		}
 
@@ -220,7 +222,7 @@ func Build(f BuildFunc, options ...Option) {
 
 	if !result.Launch.isEmpty() {
 		if apiVersion.LessThan(apiV05) && len(result.Launch.BOM) > 0 {
-			config.exitHandler.Error(fmt.Errorf("BOM entries in launch.toml is only supported with Buildpack API v0.5 or higher"))
+			config.exitHandler.Error(errors.New("BOM entries in launch.toml is only supported with Buildpack API v0.5 or higher"))
 			return
 		}
 
@@ -237,6 +239,15 @@ func Build(f BuildFunc, options ...Option) {
 		}
 
 		launch.Processes = result.Launch.Processes
+		if apiVersion.LessThan(apiV06) {
+			for _, process := range launch.Processes {
+				if process.Default {
+					config.exitHandler.Error(errors.New("processes can only be marked as default with Buildpack API v0.6 or higher"))
+					return
+				}
+			}
+		}
+
 		launch.Slices = result.Launch.Slices
 		launch.BOM = result.Launch.BOM
 		if len(result.Launch.Labels) > 0 {

build_test.go

@@ -72,7 +72,7 @@ func testBuild(t *testing.T, context spec.G, it spec.S) {
 		Expect(err).NotTo(HaveOccurred())
 
 		bpTOML := []byte(`
-api = "0.5"
+api = "0.6"
 [buildpack]
   id = "some-id"
   name = "some-name"
@@ -175,6 +175,7 @@ api = "0.4"
 `))
 			})
 		})
+
 		context("when the api version is greater or equal to 0.5", func() {
 			it("throws an error", func() {
 				packit.Build(func(ctx packit.BuildContext) (packit.BuildResult, error) {
@@ -543,7 +544,7 @@ api = "0.4"
 			`))
 		})
 
-		context("when using the deprecated api", func() {
+		context("when the process is the default", func() {
 			it("persists a launch.toml", func() {
 				packit.Build(func(ctx packit.BuildContext) (packit.BuildResult, error) {
 					return packit.BuildResult{
@@ -554,6 +555,7 @@ api = "0.4"
 									Command: "some-command",
 									Args:    []string{"some-arg"},
 									Direct:  true,
+									Default: true,
 								},
 							},
 						},
@@ -569,9 +571,43 @@ api = "0.4"
 						command = "some-command"
 						args = ["some-arg"]
 						direct = true
+						default = true
 				`))
 			})
 		})
+
+		context("when the api version is less than 0.6", func() {
+			it.Before(func() {
+				Expect(os.WriteFile(filepath.Join(cnbDir, "buildpack.toml"), []byte(`
+api = "0.5"
+[buildpack]
+  id = "some-id"
+  name = "some-name"
+  version = "some-version"
+  clear-env = false
+`), 0600)).To(Succeed())
+			})
+
+			it("errors", func() {
+				packit.Build(func(ctx packit.BuildContext) (packit.BuildResult, error) {
+					return packit.BuildResult{
+						Launch: packit.LaunchMetadata{
+							Processes: []packit.Process{
+								{
+									Type:    "some-type",
+									Command: "some-command",
+									Args:    []string{"some-arg"},
+									Direct:  true,
+									Default: true,
+								},
+							},
+						},
+					}, nil
+				}, packit.WithArgs([]string{binaryPath, layersDir, platformDir, planPath}), packit.WithExitHandler(exitHandler))
+
+				Expect(exitHandler.ErrorCall.Receives.Error).To(MatchError(ContainSubstring("processes can only be marked as default with Buildpack API v0.6 or higher")))
+			})
+		})
 	})
 
 	context("when there are slices in the result", func() {
@@ -596,30 +632,6 @@ api = "0.4"
 					paths = ["some-slice"]
 			`))
 		})
-
-		context("when using the deprecated api", func() {
-			it("persists a launch.toml", func() {
-				packit.Build(func(ctx packit.BuildContext) (packit.BuildResult, error) {
-					return packit.BuildResult{
-						Launch: packit.LaunchMetadata{
-							Slices: []packit.Slice{
-								{
-									Paths: []string{"some-slice"},
-								},
-							},
-						},
-					}, nil
-				}, packit.WithArgs([]string{binaryPath, layersDir, platformDir, planPath}))
-
-				contents, err := os.ReadFile(filepath.Join(layersDir, "launch.toml"))
-				Expect(err).NotTo(HaveOccurred())
-
-				Expect(string(contents)).To(MatchTOML(`
-					[[slices]]
-						paths = ["some-slice"]
-				`))
-			})
-		})
 	})
 
 	context("when there are labels in the result", func() {
@@ -648,34 +660,6 @@ api = "0.4"
 					value = "some-other-value"
 			`))
 		})
-
-		context("when using the deprecated api", func() {
-			it("persists a launch.toml", func() {
-				packit.Build(func(ctx packit.BuildContext) (packit.BuildResult, error) {
-					return packit.BuildResult{
-						Launch: packit.LaunchMetadata{
-							Labels: map[string]string{
-								"some key":       "some value",
-								"some-other-key": "some-other-value",
-							},
-						},
-					}, nil
-				}, packit.WithArgs([]string{binaryPath, layersDir, platformDir, planPath}))
-
-				contents, err := os.ReadFile(filepath.Join(layersDir, "launch.toml"))
-				Expect(err).NotTo(HaveOccurred())
-
-				Expect(string(contents)).To(MatchTOML(`
-					[[labels]]
-						key = "some key"
-						value = "some value"
-
-					[[labels]]
-						key = "some-other-key"
-						value = "some-other-value"
-				`))
-			})
-		})
 	})
 
 	context("when there are no processes, slices, bom or labels in the result", func() {

process.go

@@ -19,4 +19,7 @@ type Process struct {
 
 	// Direct indicates whether the process should bypass the shell when invoked.
 	Direct bool `toml:"direct"`
+
+	// Default indicates if this process should be the default when launched.
+	Default bool `toml:"default,omitempty"`
 }