Support local features provides inside .devcontainer dir

This allows features to be provided inside the .devcontainer directory
rather than downloaded from a registry, matching the behavior of the
official devcontainer tooling.

For example, Kubernetes tooling generates a devcontainer.json
containing:

    "features": {
        "ghcr.io/devcontainers/features/docker-outside-of-docker:1": {
            "enableNonRootDocker": "true",
            "moby": "true"
        },
        "ghcr.io/devcontainers/features/kubectl-helm-minikube:1": {},
        "./local-features/copy-kube-config": {}
    },

devcontainer/devcontainer.go

@@ -169,14 +169,14 @@ func (s *Spec) Compile(fs billy.Filesystem, devcontainerDir, scratchDir, fallbac
 	if remoteUser == "" {
 		remoteUser = params.User
 	}
-	params.DockerfileContent, err = s.compileFeatures(fs, scratchDir, params.User, remoteUser, params.DockerfileContent)
+	params.DockerfileContent, err = s.compileFeatures(fs, devcontainerDir, scratchDir, params.User, remoteUser, params.DockerfileContent)
 	if err != nil {
 		return nil, err
 	}
 	return params, nil
 }
 
-func (s *Spec) compileFeatures(fs billy.Filesystem, scratchDir, containerUser, remoteUser, dockerfileContent string) (string, error) {
+func (s *Spec) compileFeatures(fs billy.Filesystem, devcontainerDir, scratchDir, containerUser, remoteUser, dockerfileContent string) (string, error) {
 	// If there are no features, we don't need to do anything!
 	if len(s.Features) == 0 {
 		return dockerfileContent, nil
@@ -200,9 +200,16 @@ func (s *Spec) compileFeatures(fs billy.Filesystem, scratchDir, containerUser, r
 	sort.Strings(featureOrder)
 
 	for _, featureRefRaw := range featureOrder {
-		featureRefParsed, err := name.NewTag(featureRefRaw)
-		if err != nil {
-			return "", fmt.Errorf("parse feature ref %s: %w", featureRefRaw, err)
+		var (
+			featureRef string
+			ok         bool
+		)
+		if _, featureRef, ok = strings.Cut(featureRefRaw, "./"); !ok {
+			featureRefParsed, err := name.NewTag(featureRefRaw)
+			if err != nil {
+				return "", fmt.Errorf("parse feature ref %s: %w", featureRefRaw, err)
+			}
+			featureRef = featureRefParsed.Repository.Name()
 		}
 
 		featureOpts := map[string]any{}
@@ -222,13 +229,13 @@ func (s *Spec) compileFeatures(fs billy.Filesystem, scratchDir, containerUser, r
 		// devcontainers/cli has a very complex method of computing the feature
 		// name from the feature reference. We're just going to hash it for simplicity.
 		featureSha := md5.Sum([]byte(featureRefRaw))
-		featureName := filepath.Base(featureRefParsed.Repository.Name())
+		featureName := filepath.Base(featureRef)
 		featureDir := filepath.Join(featuresDir, fmt.Sprintf("%s-%x", featureName, featureSha[:4]))
 		err = fs.MkdirAll(featureDir, 0644)
 		if err != nil {
 			return "", err
 		}
-		spec, err := features.Extract(fs, featureDir, featureRefRaw)
+		spec, err := features.Extract(fs, devcontainerDir, featureDir, featureRefRaw)
 		if err != nil {
 			return "", fmt.Errorf("extract feature %s: %w", featureRefRaw, err)
 		}

devcontainer/features/features.go

@@ -16,23 +16,22 @@ import (
 	"github.com/go-git/go-billy/v5"
 	"github.com/google/go-containerregistry/pkg/name"
 	"github.com/google/go-containerregistry/pkg/v1/remote"
+	"github.com/otiai10/copy"
 	"github.com/tailscale/hujson"
 )
 
-// Extract unpacks the feature from the image and returns the
-// parsed specification.
-func Extract(fs billy.Filesystem, directory, reference string) (*Spec, error) {
+func extractFromImage(fs billy.Filesystem, directory, reference string) error {
 	ref, err := name.ParseReference(reference)
 	if err != nil {
-		return nil, fmt.Errorf("parse feature ref %s: %w", reference, err)
+		return fmt.Errorf("parse feature ref %s: %w", reference, err)
 	}
 	image, err := remote.Image(ref)
 	if err != nil {
-		return nil, fmt.Errorf("fetch feature image %s: %w", reference, err)
+		return fmt.Errorf("fetch feature image %s: %w", reference, err)
 	}
 	manifest, err := image.Manifest()
 	if err != nil {
-		return nil, fmt.Errorf("fetch feature manifest %s: %w", reference, err)
+		return fmt.Errorf("fetch feature manifest %s: %w", reference, err)
 	}
 
 	var tarLayer *tar.Reader
@@ -42,17 +41,17 @@ func Extract(fs billy.Filesystem, directory, reference string) (*Spec, error) {
 		}
 		layer, err := image.LayerByDigest(manifestLayer.Digest)
 		if err != nil {
-			return nil, fmt.Errorf("fetch feature layer %s: %w", reference, err)
+			return fmt.Errorf("fetch feature layer %s: %w", reference, err)
 		}
 		layerReader, err := layer.Uncompressed()
 		if err != nil {
-			return nil, fmt.Errorf("uncompress feature layer %s: %w", reference, err)
+			return fmt.Errorf("uncompress feature layer %s: %w", reference, err)
 		}
 		tarLayer = tar.NewReader(layerReader)
 		break
 	}
 	if tarLayer == nil {
-		return nil, fmt.Errorf("no tar layer found with media type %q: are you sure this is a devcontainer feature?", TarLayerMediaType)
+		return fmt.Errorf("no tar layer found with media type %q: are you sure this is a devcontainer feature?", TarLayerMediaType)
 	}
 
 	for {
@@ -61,35 +60,60 @@ func Extract(fs billy.Filesystem, directory, reference string) (*Spec, error) {
 			break
 		}
 		if err != nil {
-			return nil, fmt.Errorf("read feature layer %s: %w", reference, err)
+			return fmt.Errorf("read feature layer %s: %w", reference, err)
 		}
 		path := filepath.Join(directory, header.Name)
 		switch header.Typeflag {
 		case tar.TypeDir:
 			err = fs.MkdirAll(path, 0755)
 			if err != nil {
-				return nil, fmt.Errorf("mkdir %s: %w", path, err)
+				return fmt.Errorf("mkdir %s: %w", path, err)
 			}
 		case tar.TypeReg:
 			outFile, err := fs.Create(path)
 			if err != nil {
-				return nil, fmt.Errorf("create %s: %w", path, err)
+				return fmt.Errorf("create %s: %w", path, err)
 			}
 			_, err = io.Copy(outFile, tarLayer)
 			if err != nil {
-				return nil, fmt.Errorf("copy %s: %w", path, err)
+				return fmt.Errorf("copy %s: %w", path, err)
 			}
 			err = outFile.Close()
 			if err != nil {
-				return nil, fmt.Errorf("close %s: %w", path, err)
+				return fmt.Errorf("close %s: %w", path, err)
 			}
 		default:
-			return nil, fmt.Errorf("unknown type %d in %s", header.Typeflag, path)
+			return fmt.Errorf("unknown type %d in %s", header.Typeflag, path)
+		}
+	}
+	return nil
+}
+
+// Extract unpacks the feature from the image and returns the
+// parsed specification.
+func Extract(fs billy.Filesystem, devcontainerDir, directory, reference string) (*Spec, error) {
+	if strings.HasPrefix(reference, "./") {
+		if err := copy.Copy(filepath.Join(devcontainerDir, reference), directory, copy.Options{
+			PreserveTimes: true,
+			PreserveOwner: true,
+			OnSymlink: func(src string) copy.SymlinkAction {
+				return copy.Shallow
+			},
+			OnError: func(src, dest string, err error) error {
+				if err == nil {
+					return nil
+				}
+				return fmt.Errorf("copy error: %q -> %q: %w", reference, directory, err)
+			},
+		}); err != nil {
+			return nil, err
 		}
+	} else if err := extractFromImage(fs, directory, reference); err != nil {
+		return nil, err
 	}
 
 	installScriptPath := filepath.Join(directory, "install.sh")
-	_, err = fs.Stat(installScriptPath)
+	_, err := fs.Stat(installScriptPath)
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
 			return nil, errors.New("install.sh must be in the root of the feature")

devcontainer/features/features_test.go

@@ -17,7 +17,7 @@ func TestExtract(t *testing.T) {
 		registry := registrytest.New(t)
 		ref := registrytest.WriteContainer(t, registry, "coder/test:latest", "some/type", nil)
 		fs := memfs.New()
-		_, err := features.Extract(fs, "/", ref)
+		_, err := features.Extract(fs, "", "/", ref)
 		require.ErrorContains(t, err, "no tar layer found")
 	})
 	t.Run("MissingInstallScript", func(t *testing.T) {
@@ -27,7 +27,7 @@ func TestExtract(t *testing.T) {
 			"devcontainer-feature.json": "{}",
 		})
 		fs := memfs.New()
-		_, err := features.Extract(fs, "/", ref)
+		_, err := features.Extract(fs, "", "/", ref)
 		require.ErrorContains(t, err, "install.sh")
 	})
 	t.Run("MissingFeatureFile", func(t *testing.T) {
@@ -37,7 +37,7 @@ func TestExtract(t *testing.T) {
 			"install.sh": "hey",
 		})
 		fs := memfs.New()
-		_, err := features.Extract(fs, "/", ref)
+		_, err := features.Extract(fs, "", "/", ref)
 		require.ErrorContains(t, err, "devcontainer-feature.json")
 	})
 	t.Run("MissingFeatureProperties", func(t *testing.T) {
@@ -48,7 +48,7 @@ func TestExtract(t *testing.T) {
 			"devcontainer-feature.json": features.Spec{},
 		})
 		fs := memfs.New()
-		_, err := features.Extract(fs, "/", ref)
+		_, err := features.Extract(fs, "", "/", ref)
 		require.ErrorContains(t, err, "id is required")
 	})
 	t.Run("Success", func(t *testing.T) {
@@ -63,7 +63,7 @@ func TestExtract(t *testing.T) {
 			},
 		})
 		fs := memfs.New()
-		_, err := features.Extract(fs, "/", ref)
+		_, err := features.Extract(fs, "", "/", ref)
 		require.NoError(t, err)
 	})
 }

go.mod

@@ -24,6 +24,7 @@ require (
 	github.com/google/go-containerregistry v0.15.2
 	github.com/kballard/go-shellquote v0.0.0-20180428030007-95032a82bc51
 	github.com/mattn/go-isatty v0.0.19
+	github.com/otiai10/copy v1.14.0
 	github.com/sirupsen/logrus v1.9.3
 	github.com/spf13/cobra v1.7.0
 	github.com/stretchr/testify v1.8.4
@@ -186,7 +187,6 @@ require (
 	github.com/opencontainers/runc v1.1.5 // indirect
 	github.com/opencontainers/runtime-spec v1.1.0-rc.1 // indirect
 	github.com/opencontainers/selinux v1.11.0 // indirect
-	github.com/otiai10/copy v1.12.0 // indirect
 	github.com/pjbgf/sha1cd v0.3.0 // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect

go.sum

@@ -725,8 +725,8 @@ github.com/opencontainers/selinux v1.10.0/go.mod h1:2i0OySw99QjzBBQByd1Gr9gSjvuh
 github.com/opencontainers/selinux v1.11.0 h1:+5Zbo97w3Lbmb3PeqQtpmTkMwsW5nRI3YaLpt7tQ7oU=
 github.com/opencontainers/selinux v1.11.0/go.mod h1:E5dMC3VPuVvVHDYmi78qvhJp8+M586T4DlDRYpFkyec=
 github.com/ory/dockertest/v3 v3.10.0 h1:4K3z2VMe8Woe++invjaTB7VRyQXQy5UY+loujO4aNE4=
-github.com/otiai10/copy v1.12.0 h1:cLMgSQnXBs1eehF0Wy/FAGsgDTDmAqFR7rQylBb1nDY=
-github.com/otiai10/copy v1.12.0/go.mod h1:rSaLseMUsZFFbsFGc7wCJnnkTAvdc5L6VWxPE4308Ww=
+github.com/otiai10/copy v1.14.0 h1:dCI/t1iTdYGtkvCuBG2BgR6KZa83PTclw4U5n2wAllU=
+github.com/otiai10/copy v1.14.0/go.mod h1:ECfuL02W+/FkTWZWgQqXPWZgW9oeKCSQ5qVfSc4qc4w=
 github.com/otiai10/mint v1.5.1 h1:XaPLeE+9vGbuyEHem1JNk3bYc7KKqyI/na0/mLd/Kks=
 github.com/pelletier/go-toml v1.9.5 h1:4yBQzkHv+7BHq2PQUZF3Mx0IYxG7LsP222s7Agd3ve8=
 github.com/pelletier/go-toml/v2 v2.0.8 h1:0ctb6s9mE31h0/lhu+J6OPmVeDxJn+kYnJc2jZR9tGQ=

integration/integration_test.go

@@ -110,6 +110,18 @@ func TestBuildFromDevcontainerWithFeatures(t *testing.T) {
 		"install.sh": "echo $PINEAPPLE > /test2output",
 	})
 
+	feature3Spec, err := json.Marshal(features.Spec{
+		ID:      "test3",
+		Name:    "test3",
+		Version: "1.0.0",
+		Options: map[string]features.Option{
+			"grape": {
+				Type: "string",
+			},
+		},
+	})
+	require.NoError(t, err)
+
 	// Ensures that a Git repository with a devcontainer.json is cloned and built.
 	url := createGitServer(t, gitServerOptions{
 		files: map[string]string{
@@ -124,10 +136,15 @@ func TestBuildFromDevcontainerWithFeatures(t *testing.T) {
 					},
 					"` + feature2Ref + `": {
 						"pineapple": "hello from test 2!"
+					},
+					"./feature3": {
+						"grape": "hello from test 3!"
 					}
 				}
 			}`,
-			".devcontainer/Dockerfile": "FROM ubuntu",
+			".devcontainer/Dockerfile":                         "FROM ubuntu",
+			".devcontainer/feature3/devcontainer-feature.json": string(feature3Spec),
+			".devcontainer/feature3/install.sh":                "echo $GRAPE > /test3output",
 		},
 	})
 	ctr, err := runEnvbuilder(t, options{env: []string{
@@ -140,6 +157,9 @@ func TestBuildFromDevcontainerWithFeatures(t *testing.T) {
 
 	test2Output := execContainer(t, ctr, "cat /test2output")
 	require.Equal(t, "hello from test 2!", strings.TrimSpace(test2Output))
+
+	test3Output := execContainer(t, ctr, "cat /test3output")
+	require.Equal(t, "hello from test 3!", strings.TrimSpace(test3Output))
 }
 
 func TestBuildFromDockerfile(t *testing.T) {