pre-push: pushing annotated tags crashes with "Failed to find merge base: object is no commit object"

[Colourlessglow]

Repro

Any repo with an hk-managed pre-push hook:

git tag -a v1.0.0 -m v1.0.0
git push origin v1.0.0

or by simulating the git hook protocol directly:

echo "refs/tags/v1.0.0 <tag-object-sha> refs/tags/v1.0.0 0000000000000000000000000000000000000000" | hk run pre-push

Error

files - Fetching files between refs/remotes/origin/main and <tag-object-sha>
Error: Failed to find merge base

Caused by:
    object is no commit object; class=Invalid (3)

Location:
    src/git.rs:1678:45

The hook exits non-zero, so git aborts the push entirely.

Root cause

src/cli/run/pre_push.rs sets to_ref to the pushed ref's SHA verbatim. For annotated tags that is the tag object, not a commit. files_between_refs in src/git.rs then calls repo.merge_base(from_obj.id(), to_obj.id()), which fails with ErrorCode::Invalid for tag objects. The existing shallow-clone fallback only handles ErrorCode::NotFound, so Invalid propagates and fails the whole run.

Suggested fix

Peel the objects to commits before computing the merge base (obj.peel_to_commit()), or handle ErrorCode::Invalid the same way as NotFound — the git merge-base CLI fallback peels tags automatically.

Arguably tag-only pushes could skip file computation entirely: a tag carries no new file changes.

Impact

Any repo with an hk pre-push hook cannot push tags without --no-verify. In tag-driven release flows (pushing v* triggers the release CI), the release aborts mid-flow.

Reproduced on hk 1.54.1 and 1.55.0, macOS arm64, git 2.54.0.

[jdx]

Thanks for the detailed report and root-cause analysis. Confirmed: the failure is isolated to the libgit2 path, which passed the annotated tag object ID directly to merge_base; the shell-git path already succeeds because Git peels the tag.

Fixed in #1197 by peeling both refs to commits before calculating the merge base. The PR also adds an end-to-end annotated-tag push regression test and verifies it with both libgit2 enabled and disabled.

AI-assisted — Tool: Codex; model: openai/gpt-5; version: unavailable.