tools/clang-format.sh: cache clang-format in the common git dir

[moonchen]

Problem

In a linked git worktree, cmake --build build -t format and the pre-commit hook fail with No clang-format found. tools/clang-format.sh resolves its download/cache directory with git rev-parse --absolute-git-dir, which in a worktree is the per-worktree git dir (.git/worktrees/<name>), not the shared .git. clang-format is installed once under the common dir, so the worktree looks in the wrong, empty place.

Fix

Resolve the common git dir, which is shared by all worktrees — the same thing CMakeLists.txt already does to compute GIT_COMMON_DIR, so the script and CMake now agree on the cache location. --git-common-dir can return a relative path, so it is made absolute with cd … && pwd.

I deliberately avoided git rev-parse --path-format=absolute --git-common-dir: that exact form was removed in #11495 for a cmake 3.28 incompatibility (it needs git 2.31+). This restores the worktree support originally added in #11015 without reverting the #11495 fix.

Only clang-format.sh is affected — yapf.sh/cmake-format.sh now use uv and no longer cache under the git dir.

Testing (git 2.43.0, cmake 3.28.3)

• Main checkout: pre-commit hook and format target behave as before.
• Linked worktree, with the binary installed only under the common .git/fmt: the pre-commit hook now finds clang-format and commits succeed (previously No clang-format found) — verified end-to-end with the clangFormat.binary fallback removed.

[Copilot]

Pull request overview

This PR fixes formatter installation/cache lookup under git worktree setups by updating tools/clang-format.sh to cache/download clang-format under the common Git directory (shared across linked worktrees), aligning the script’s behavior with how CMakeLists.txt computes GIT_COMMON_DIR.

Changes:

• Switch clang-format cache root from git rev-parse --absolute-git-dir to an absolute git rev-parse --git-common-dir.
• Update the sourced-script path logic (used by the pre-commit hook) to use the common Git dir cache location as well.

[moonchen]

Testing

Tested the format workflows from a fresh clone, comparing master with this PR.

Does clang-format get found and run? — verified two ways: cache-dir resolution, and a real pre-commit commit.

Workflow	master	PR #13302
No worktree	✅ works	✅ works
Linked worktree	❌ No clang-format found	✅ works

clang-format is installed once under the common .git/fmt; on master a linked worktree looks in .git/worktrees/<name>/fmt instead and misses it.

Everything checked:

Check
git 2.43.0 (current)	✅
git 2.30.2 (pre---path-format)	✅
cmake 3.28.3 (the version named in #11495)	✅
cmake format targets (clang-format-install, clang-format-src) run in a worktree	✅
--install downloads to the common .git/fmt	✅
worktree finds the --install download	✅
no-path run formats the current worktree, not the main checkout (Copilot's note)	✅

Addressing #11495: that PR removed git rev-parse --path-format=absolute --git-common-dir because it "didn't work in cmake 3.28." The real cause is the git version, not cmake — --path-format only exists in git 2.31+, and on older git (2.30.2) that command returns the literal string --path-format=absolute. This PR gets the same result (the absolute path to the shared git dir) without that flag, using cd "$(git rev-parse --git-common-dir)" && pwd — so it restores worktree support and works on git back to 2.5.