Added the ability to specify build targets for kaniko build and an option to skip building unused layers

Author: Hamish

devcontainer/devcontainer.go

@@ -69,6 +69,7 @@ type Compiled struct {
 	BuildContext      string
 	FeatureContexts   map[string]string
 	BuildArgs         []string
+	Target			  string
 
 	User         string
 	ContainerEnv map[string]string
@@ -140,6 +141,7 @@ func (s Spec) HasDockerfile() bool {
 func (s *Spec) Compile(fs billy.Filesystem, devcontainerDir, scratchDir string, fallbackDockerfile, workspaceFolder string, useBuildContexts bool, lookupEnv func(string) (string, bool)) (*Compiled, error) {
 	params := &Compiled{
 		User:         s.ContainerUser,
+		Target:       s.Build.Target,
 		ContainerEnv: s.ContainerEnv,
 		RemoteEnv:    s.RemoteEnv,
 	}

docs/env-variables.md

@@ -24,6 +24,7 @@
 | `--ignore-paths` | `ENVBUILDER_IGNORE_PATHS` |  | The comma separated list of paths to ignore when building the workspace. |
 | `--build-secrets` | `ENVBUILDER_BUILD_SECRETS` |  | The list of secret environment variables to use when building the image. |
 | `--skip-rebuild` | `ENVBUILDER_SKIP_REBUILD` |  | Skip building if the MagicFile exists. This is used to skip building when a container is restarting. e.g. docker stop -> docker start This value can always be set to true - even if the container is being started for the first time. |
+| `--skip-unused-stages` | `ENVBUILDER_SKIP_UNUSED_STAGES` |  | Skip building all unused docker stages. Otherwise it builds by default all stages, even the unnecessary ones until it reaches the target stage / end of Dockerfile. |
 | `--git-url` | `ENVBUILDER_GIT_URL` |  | The URL of a Git repository containing a Devcontainer or Docker image to clone. This is optional. |
 | `--git-clone-depth` | `ENVBUILDER_GIT_CLONE_DEPTH` |  | The depth to use when cloning the Git repository. |
 | `--git-clone-single-branch` | `ENVBUILDER_GIT_CLONE_SINGLE_BRANCH` |  | Clone only a single branch of the Git repository. |

envbuilder.go

@@ -539,6 +539,8 @@ func run(ctx context.Context, opts options.Options, execArgs *execArgsInfo) erro
 				CustomPlatform:     platforms.Format(platforms.Normalize(platforms.DefaultSpec())),
 				SnapshotMode:       "redo",
 				RunV2:              true,
+				SkipUnusedStages:   opts.SkipUnusedStages,
+				Target:				buildParams.Target,
 				RunStdout:          stdoutWriter,
 				RunStderr:          stderrWriter,
 				Destinations:       destinations,

options/options.go

@@ -100,6 +100,10 @@ type Options struct {
 	// This value can always be set to true - even if the container is being
 	// started for the first time.
 	SkipRebuild bool
+	// SkipUnusedStages builds only used stages if defined to true. Otherwise,
+	// it builds by default all stages, even the unnecessary ones until it
+	// reaches the target stage / end of Dockerfile
+	SkipUnusedStages bool
 	// GitURL is the URL of the Git repository to clone. This is optional.
 	GitURL string
 	// GitCloneDepth is the depth to use when cloning the Git repository.
@@ -357,6 +361,14 @@ func (o *Options) CLI() serpent.OptionSet {
 				"docker start This value can always be set to true - even if the " +
 				"container is being started for the first time.",
 		},
+		{
+			Flag:  "skip-unused-stages",
+			Env:   WithEnvPrefix("SKIP_UNUSED_STAGES"),
+			Value: serpent.BoolOf(&o.SkipUnusedStages),
+			Description: "Skip building all unused docker stages. Otherwise it builds by " +
+				"default all stages, even the unnecessary ones until it reaches the " +
+				"target stage / end of Dockerfile.",
+		},
 		{
 			Flag:        "git-url",
 			Env:         WithEnvPrefix("GIT_URL"),

options/testdata/options.golden

@@ -173,6 +173,10 @@ OPTIONS:
           when a container is restarting. e.g. docker stop -> docker start This
           value can always be set to true - even if the container is being
           started for the first time.
+      --skip-unused-stages bool, $ENVBUILDER_SKIP_UNUSED_STAGES
+         Skip building all unused docker stages. Otherwise it builds by default
+          all stages, even the unnecessary ones until it reaches the target
+          stage / end of Dockerfile.
 
       --ssl-cert-base64 string, $ENVBUILDER_SSL_CERT_BASE64
           The content of an SSL cert file. This is useful for self-signed