pre-push fails with `fatal: bad revision '<default-branch>'` when the default branch has no local ref

[alechemy]

Description

pre-push hard-fails and blocks the push in any clone where the remote's default branch does not exist as a local branch, and the branch being pushed has no resolvable upstream (i.e. the normal first push of a new feature branch).

Repo.PushFiles() (internal/git/repo.go#L189) falls back like this:

1. git diff --name-only HEAD @{push} — fails on a branch with no upstream.
2. resolveHeadBranch() reads .git/refs/remotes/origin/HEAD and returns the bare branch name (main), then runs git diff --name-only HEAD main --.
3. If no head branch can be resolved at all → git ls-tree -r --name-only HEAD.

Step 2 reads the remote's default branch name but then diffs against the local branch of that name. If that local branch doesn't exist, git exits 128 with fatal: bad revision 'main'. The error is returned rather than treated as a skip, so every job in the hook fails and the push is rejected.

The push-files computation runs unconditionally for pre-push as the "skip if nothing to push" gate in buildCommand (HookUsesPushFiles), so this happens even when no job references {push_files} or {files} at all — as in the config below, which is two whole-project typechecks. The computed list is only tested for emptiness and then discarded, so the hook dies on a value it never uses.

Setting a hook-level or command-level files: does not help — that only feeds the {files} template and does not replace the built-in push-files source.

Note that step 3 is a graceful fallback (ls-tree always works). It's only reachable when origin/HEAD is absent, so a clone with less remote information works fine while a normal clone with origin/HEAD set fails. Deleting refs/remotes/origin/HEAD is currently a working (if perverse) workaround.

Related: #1454 covers the same fallback picking a stale local default branch (wrong file list); this report is the harder failure where the local branch is missing entirely (push blocked). #1396 previously fixed the pathspec ambiguity on this same line.

lefthook.yml

pre-push:
  commands:
    probe:
      run: echo RAN

No {push_files} / {files} template anywhere — the failure does not depend on one.

Commands to reproduce

export LEFTHOOK_VERBOSE=true

# a remote whose default branch is `main`
git init --bare -q -b main remote.git
git init -q -b main seed && cd seed
echo hi > file.txt && git add -A && git commit -q -m init
git remote add origin ../remote.git && git push -q origin main
cd ..

git clone -q remote.git work && cd work
printf 'pre-push:\n  commands:\n    probe:\n      run: echo RAN\n' > lefthook.yml
git add -A && git commit -q -m cfg
lefthook install

# a clone that has no local `main` — e.g. someone who always branches
# straight off `origin/main` and doesn't keep a local default branch
git switch -q -c feature
git branch -D main

git push origin feature

Output:

╭─────────────────────────────────────╮
│ lefthook  v2.1.10   hook:  pre-push │
╰─────────────────────────────────────╯
│  [lefthook] git: git diff --name-only HEAD @{push}
│  > git diff --name-only HEAD @{push}
│    fatal: no upstream configured for branch 'feature'
│
│  [lefthook] git: git diff --name-only HEAD main --
│  > git diff --name-only HEAD main --
│    fatal: bad revision 'main'
│
│  probe (skip) exit status 128
  ────────────────────────────────────
summary: (done in 0.05 seconds)
✗ probe: exit status 128 (0.05 seconds)
error: failed to push some refs to '.../remote.git'

git branch main origin/main in the clone makes the same push succeed, which confirms the cause. The local branch never needs to be current — it only needs to exist.

Lefthook version

2.1.10 8d9cfec5f52367af6374a5430b4e9568844856e5 (also reproduced on 2.1.9)

Possible solution

Any of these would fix it, roughly in order of preference:

1. Resolve the fallback against the remote-tracking ref (origin/main) rather than the bare local name, since origin/HEAD is where the name came from. This also addresses the staleness in {push_files} can include stale local default-branch files when @{push} is unavailable #1454.
2. Fall through to the existing git ls-tree -r --name-only HEAD branch when the fallback diff fails, instead of propagating the error — the graceful path already exists one branch up.
3. At minimum, don't fail the whole hook on it: a push-files computation that no job consumes should not be able to reject a push.