fix(compose): hash symlinked local-feature content for reattach

CHANGELOG.md

@@ -7,6 +7,20 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [0.5.3] - 2026-10-28
+
+### Fixed
+
+- **compose** — the compose inputs hash (`LabelComposeInputsHash`) skipped
+  symlinks in a local feature's directory, while the feature build context
+  copies each symlink as the content it names. Editing the target of a
+  symlinked file (say `install.sh` linked to a shared script outside the
+  feature) left the hash unchanged, so `Up` reattached to the image built
+  from the old content. Symlinks are now hashed as their resolved content;
+  a symlink to a directory fails the hash, so that workspace gets no label
+  and always takes the full path. Found by the DAP review bot on the
+  v0.5.2 bump.
+
 ## [0.5.2] - 2026-10-28
 
 ### Fixed
@@ -667,7 +681,8 @@ shelling out to `@devcontainers/cli`.
 - `events` is doc-tagged **experimental** until v1.0.0 — type shapes may evolve
   without a SemVer-major bump.
 
-[Unreleased]: https://github.com/crunchloop/devcontainer/compare/v0.5.2...HEAD
+[Unreleased]: https://github.com/crunchloop/devcontainer/compare/v0.5.3...HEAD
+[0.5.3]: https://github.com/crunchloop/devcontainer/compare/v0.5.2...v0.5.3
 [0.5.2]: https://github.com/crunchloop/devcontainer/compare/v0.5.1...v0.5.2
 [0.5.1]: https://github.com/crunchloop/devcontainer/compare/v0.5.0...v0.5.1
 [0.5.0]: https://github.com/crunchloop/devcontainer/compare/v0.4.3...v0.5.0

up_compose_reattach.go

@@ -176,15 +176,20 @@ func (e *Engine) composeInputsHash(cfg *config.ResolvedConfig, opts UpOptions, p
 	return hex.EncodeToString(sum[:]), nil
 }
 
-// hashDirContent digests every regular file under root (relative path,
-// mode and bytes, in lexical order), reading at most limit bytes.
+// hashDirContent digests every regular file and symlink under root
+// (relative path, mode and bytes, in lexical order), reading at most
+// limit bytes. A symlink is hashed as the content it resolves to, the
+// same way feature.GenerateBuildContext copies it into the build
+// context, so editing a linked file outside the feature directory
+// changes the digest. A symlink to a directory, which the build
+// context copy cannot handle either, fails the hash.
 func hashDirContent(root string, limit int64) (string, error) {
 	var paths []string
 	err := filepath.WalkDir(root, func(p string, d fs.DirEntry, err error) error {
 		if err != nil {
 			return err
 		}
-		if d.Type().IsRegular() {
+		if d.Type().IsRegular() || d.Type()&fs.ModeSymlink != 0 {
 			paths = append(paths, p)
 		}
 		return nil
@@ -200,10 +205,13 @@ func hashDirContent(root string, limit int64) (string, error) {
 		if err != nil {
 			return "", err
 		}
-		fi, err := os.Stat(p)
+		fi, err := os.Stat(p) // follows a symlink to the content it names
 		if err != nil {
 			return "", err
 		}
+		if !fi.Mode().IsRegular() {
+			return "", fmt.Errorf("%s: not a regular file", rel)
+		}
 		total += fi.Size()
 		if total > limit {
 			return "", fmt.Errorf("content exceeds %d bytes", limit)

up_compose_reattach_test.go

@@ -177,6 +177,44 @@ func TestComposeInputsHash_LocalFeatureContent(t *testing.T) {
 	}
 }
 
+// A local feature file that is a symlink is copied into the build
+// context as the content it names, so that content is what the hash
+// covers: editing the link's target outside the feature directory must
+// not let a reattach keep the image built from the old content.
+func TestComposeInputsHash_LocalFeatureSymlinkTarget(t *testing.T) {
+	dir := t.TempDir()
+	json := replaceOnce(t, hashBaseJSON, `"ghcr.io/devcontainers/features/docker-in-docker:2": { "moby": false }`, `"./local-feature": {}`)
+	featDir := filepath.Join(dir, ".devcontainer", "local-feature")
+	if err := os.MkdirAll(featDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	shared := filepath.Join(dir, "shared-install.sh")
+	if err := os.WriteFile(shared, []byte("#!/bin/sh\necho one\n"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Symlink("../../shared-install.sh", filepath.Join(featDir, "install.sh")); err != nil {
+		t.Fatal(err)
+	}
+	f := newHashFixture(t, dir, json, hashBaseCompose)
+	h1 := f.hash(t, "sha256:base")
+	if err := os.WriteFile(shared, []byte("#!/bin/sh\necho two\n"), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if h2 := f.hash(t, "sha256:base"); h1 == h2 {
+		t.Fatal("hash unchanged after editing the target of a symlinked install.sh")
+	}
+
+	// A symlink to a directory cannot be copied into the build context
+	// either; the hash fails (no label, so no reattach) instead of
+	// silently skipping it.
+	if err := os.Symlink(dir, filepath.Join(featDir, "loop")); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := f.eng.composeInputsHash(f.cfg, f.opts, f.project, "sha256:base"); err == nil {
+		t.Fatal("hash computed over a symlink to a directory")
+	}
+}
+
 func TestComposeInputsHash_RequiresBaseImageID(t *testing.T) {
 	f := newHashFixture(t, t.TempDir(), hashBaseJSON, hashBaseCompose)
 	if _, err := f.eng.composeInputsHash(f.cfg, f.opts, f.project, ""); err == nil {