Introduce BP_DIRECT_PROCESS to enable run images without shell

README.md

@@ -16,6 +16,10 @@ The buildpack will do the following:
   * If process types are identified from environment _and_ Binding _or_ file, the contents are merged into a single `Procfile`. Commands from Binding or file take precedence if there are duplicate types, with Binding taking precedence over file.
   * If the application's stack is `io.paketo.stacks.tiny` the contents of the `Procfile` must be single command with zero or more space delimited arguments. Argument values containing whitespace should be quoted. The resulting process will be executed directly and will not be parsed by the shell.
   * If the application's stack is not `io.paketo.stacks.tiny` the contents of `Procfile` will be executed as a shell script.
+* If `BP_DIRECT_PROCESS` is set to `true`, the command will not be executed within a shell.
+  * This behavior will become the default with the next major version, fulfilling [RFC-0093](https://github.com/buildpacks/rfcs/blob/main/text/0093-remove-shell-processes.md). Afterwards, this option will be deprecated and removed eventually.
+
+The `BP_DIRECT_PROCESS` environment variable can be used to opt-in in starting processes directly. The next major version of this buildpack will no longer support indirect processes and all processes will be started directly. Once processes are no longer started indirectly by default, the configuration `BP_DIRECT_PROCESS` will be removed since it will have no effect.
 
 ## Bindings
 

buildpack.toml

@@ -40,5 +40,10 @@ arch = "arm64"
   include-files = ["LICENSE", "NOTICE", "README.md", "linux/amd64/bin/build", "linux/amd64/bin/detect", "linux/amd64/bin/main", "linux/arm64/bin/build", "linux/arm64/bin/detect", "linux/arm64/bin/main", "buildpack.toml"]
   pre-package = "scripts/build.sh"
 
+[[metadata.configurations]]
+    name = "BP_DIRECT_PROCESS"
+    default = "false"
+    description = "start the processes directly or with a shell"
+
 [[stacks]]
   id = "*"

procfile/build.go

@@ -25,6 +25,7 @@ import (
 	"github.com/mattn/go-shellwords"
 	"github.com/paketo-buildpacks/libpak"
 	"github.com/paketo-buildpacks/libpak/bard"
+	"github.com/paketo-buildpacks/libpak/sherpa"
 )
 
 type Build struct {
@@ -57,6 +58,7 @@ func (b Build) Build(context libcnb.BuildContext) (libcnb.BuildResult, error) {
 			process.Direct = true
 		} else {
 			process.Command = v.(string)
+			process.Direct = sherpa.ResolveBool("BP_DIRECT_PROCESS")
 		}
 
 		result.Processes = append(result.Processes, process)

procfile/build_test.go

@@ -67,6 +67,36 @@ func testBuild(t *testing.T, context spec.G, it spec.S) {
 		Expect(build.Build(ctx)).To(Equal(result))
 	})
 
+	context("given BP_DIRECT_PROCESS=true", func() {
+		it.Before(func() {
+			t.Setenv("BP_DIRECT_PROCESS", "true")
+		})
+
+		it("uses a process with direct=true", func() {
+			ctx.Plan = libcnb.BuildpackPlan{
+				Entries: []libcnb.BuildpackPlanEntry{
+					{
+						Name: "procfile",
+						Metadata: map[string]interface{}{
+							"test-type": "test-command",
+						},
+					},
+				},
+			}
+
+			result := libcnb.NewBuildResult()
+			result.Processes = append(result.Processes,
+				libcnb.Process{
+					Type:    "test-type",
+					Command: "test-command",
+					Direct:  true,
+				},
+			)
+
+			Expect(build.Build(ctx)).To(Equal(result))
+		})
+	})
+
 	context("given a special process name", func() {
 		var assertMarkedAsDefault = func(name string) {
 			ctx.Plan = libcnb.BuildpackPlan{