gastownhall/beads · error

cannot read default.nix: %v

Error message

cannot read default.nix: %v

What it means

After stat'ing default.nix, fixNixHash reads its contents with os.ReadFile to locate the vendorHash assignment. If the file exists but cannot be read (permission denied, I/O error, or it is a directory named default.nix), this error wraps the os error and aborts the fix.

Source

Thrown at cmd/bd/preflight.go:761

	if _, err := exec.LookPath("nix"); err != nil {
		return false, "", "", fmt.Errorf(
			"nix not found in PATH\n  Manual fix:\n" +
				"    1. Edit default.nix: set vendorHash = \"sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=\"\n" +
				"    2. Run: nix build .#default\n" +
				"    3. Copy the 'got:' hash from the error into default.nix",
		)
	}

	nixPath := "default.nix"
	nixInfo, err := os.Stat(nixPath)
	if err != nil {
		return false, "", "", fmt.Errorf("cannot stat default.nix: %v", err)
	}
	nixPerm := nixInfo.Mode().Perm()

	content, err := os.ReadFile(nixPath)
	if err != nil {
		return false, "", "", fmt.Errorf("cannot read default.nix: %v", err)
	}

	re := regexp.MustCompile(`(vendorHash\s*=\s*)"([^"]+)"`)
	loc := re.FindSubmatchIndex(content)
	if loc == nil {
		return false, "", "", fmt.Errorf("vendorHash not found in default.nix")
	}
	oldHash := string(content[loc[4]:loc[5]])

	const sentinel = "sha256-AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA="
	probed := append(append([]byte{}, content[:loc[4]]...), append([]byte(sentinel), content[loc[5]:]...)...)
	if err := os.WriteFile(nixPath, probed, nixPerm); err != nil {
		return false, "", "", fmt.Errorf("cannot write default.nix: %v", err)
	}

	restored := false
	defer func() {
		if !restored {

View on GitHub (pinned to 71377f2769)

Solutions

1. Check and fix permissions: `chmod u+r default.nix` (and ownership via chown if needed)
2. If the path is a directory, remove/rename it and restore the real default.nix from git: `git checkout -- default.nix`
3. Retry after fixing any underlying disk/mount error reported in the wrapped message

Example fix

// before
-rw------- default.nix  (owned by other user) -> cannot read default.nix: ...
// after
chmod u+r default.nix && bd fix

[ -r default.nix ] && [ -f default.nix ] || { echo "default.nix must be a readable file"; exit 1; }

out, err := exec.Command("bd", "fix").CombinedOutput()
if err != nil && strings.Contains(string(out), "cannot read default.nix") {
    // fix permissions/ownership, then retry
}

When it happens

Trigger: os.ReadFile("default.nix") fails during `bd fix` — e.g. file mode denies read for the current user, the file is actually a directory, or a disk/ACL problem prevents reading.

Common situations: default.nix checked in with restrictive permissions (e.g. 0600 owned by another user) in a shared CI workspace; a directory accidentally named default.nix; read-only or corrupted mount.

Related errors

• cannot write default.nix: %v
• cannot update default.nix: %v
• dolt path is not executable
• failed to create backup directory: %w
• failed to create temp file: %w

AI-assisted analysis of gastownhall/beads@71377f2769 (2026-08-30). Data as JSON: /api/errors/43a8c741ad77927e. Report an issue: GitHub.