After repo.reprojectcmd exits 0, _Reproject ran `git diff-index --cached
--name-only <revid>^{tree}` to verify that the index matches the target
commit's tree.
Peeling <revid>^{tree} and comparing every entry against the index
forces Git to read the target commit and walk every tree object in the
target revision from .git/objects.
reprojectcmd exists for virtualized filesystems such as ABFS whose
checkout command materializes the worktree and writes .git/index from
its own tree metadata without reading .git/objects/pack/*-trees-*.pack.
Running diff-index against <revid>^{tree} afterward forces Git to fault
in the tree packfiles over the network (260 FetchTrees pack downloads /
1.64 GiB across a 3,296-project Android checkout).
Trust reprojectcmd's exit status for index materialization instead of
re-walking the target tree in Git, while keeping the HEAD postcondition
check that verifies the command did not modify refs.
Bug: 543101585
Change-Id: Ie5feea41a4191245232c6763a489d01596370c55
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/643004
Commit-Queue: Gavin Mak <gavinmak@google.com>
Tested-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Brian Gan <brgan@google.com>
Add `repo.reprojectcmd`, the checkout counterpart to `repo.fetchcmd`.
When set, `repo sync` runs this command instead of Git to materialize a
project's index and worktree at the target tree, while `repo` handles
ref updates directly via `git update-ref`.
This replaces Git's tree materialization steps: detaching HEAD,
fast-forwarding, and hard-resetting. Rebasing is not delegated, and the
command is skipped if HEAD is already at the target, if HEAD is ahead of
the target during fast-forward, or for MetaProjects.
The command runs in a subshell with project environment variables (such
as `REPO_TREV`). Before running, `repo` ensures no operation is in
progress and no staged changes exist. Worktree collision detection is
delegated to the command (preserving benign unstaged/untracked edits).
Afterward, `repo` verifies that HEAD was untouched and that the index
matches the target tree.
Like `repo.fetchcmd`, this requires `repo.uselocalgitdirs`. Nested
projects and submodules are unsupported; `repo sync` fails if the
manifest contains any while `repo.reprojectcmd` is enabled.
Verified end-to-end with repo init using local-gitdirs, repo.fetchcmd,
and repo.reprojectcmd ('git -C $REPO_PATH read-tree -m -u $REPO_TREV'):
* Verified detached HEAD checkout and correct reflog generation across
projects.
* Verified benign unstaged edits and untracked files survive checkout.
* Verified conflicting untracked files fail with exit 128 without
clobbering worktree.
* Verified staged changes fail upfront before reprojectcmd is executed.
Bug: 513329573
Change-Id: I964d24d22dccffc05a9b991ad69f3a7e93268c01
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/626281
Tested-by: Gavin Mak <gavinmak@google.com>
Reviewed-by: Brian Gan <brgan@google.com>
Commit-Queue: Gavin Mak <gavinmak@google.com>
Gavin Mak