BUG: Turbo crashes with EISDIR when GIT_DIR is set in a git worktree

[bestickley]

Summary

Turbo crashes with EISDIR when GIT_DIR is set in a git worktree

Description

turbo run fails with I/O error: Is a directory (os error 21) when executed inside a git hook in a git worktree. The error occurs during the file hashing phase before any tasks are started.

Environment

• Turbo version: 2.9.1
• OS: macOS (darwin arm64)
• Package manager: pnpm 10.32.1
• Git worktree: yes (linked worktree)

Reproduction

1. Create a git worktree from a turborepo monorepo:

   git worktree add ../my-worktree my-branch

2. Run turbo with GIT_DIR set to the worktree's git directory (this is what git does automatically during hook execution):

   GIT_DIR=$(git rev-parse --git-dir) npx turbo run build

3. Turbo crashes:

   × I/O error: Is a directory (os error 21)
   ╰─▶ Is a directory (os error 21)
   

Running the same command without GIT_DIR set works fine:

npx turbo run build  # ✅ works

Root Cause

In a git worktree, git rev-parse --git-dir returns a path like:

/path/to/main-repo/.git/worktrees/my-worktree

This directory contains subdirectories (refs/, logs/) that don't exist in a normal .git directory. When GIT_DIR is set, Turbo appears to use it directly for worktree/SCM detection and attempts to read a file at a path that is actually a directory.

The error happens during the turborepo_scm::package_deps phase — after all glob/ignore processing but before any task processes are spawned (debug logs show waiting for 0 processes to exit).

Impact

This breaks all git hooks (pre-commit, pre-push, etc.) that invoke turbo in a worktree, because git automatically sets GIT_DIR when executing hooks.

Workaround

Unset GIT_DIR before calling turbo in the hook:

# .husky/pre-commit
unset GIT_DIR
pnpm turbo run build

This is safe because turbo (and git) will discover the repo by walking up from cwd and reading the .git file's gitdir: pointer, arriving at the same location.

Additional Context

• --dry-run works fine (doesn't trigger the code path)
• --ui=stream does not fix it (the error is in SCM detection, not the TUI)
• Clearing the shared worktree cache does not fix it
• The verbose debug logs show repeated git hashing failed ... Falling back to manual messages for every package, but the fatal EISDIR error is not captured in the debug log — it occurs at a lower level in Turbo's Rust I/O layer

Additional information

No response

Example

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