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Garry TanandClaude Fable 5
d4b0131636
The v1.74 racy-git fix carries the real index's mtime onto the temp copy —
but its 'touch -r … || true' meant a FAILED touch silently kept the copy's
fresh stamp, marking every entry non-racy and reopening the exact same-size-
rewrite hole. A failed touch now discards the copy and seeds from read-tree
HEAD (slower; every entry re-hashed; fingerprint stays honest).
Verification for #2687 itself: the reporter's same-size-rewrite repro run 20
iterations against this tree — 0 misses (the underlying race was fixed by
v1.74's b1485d88 with its own regression test; this wave verifies and closes,
it does not claim that fix). Receipt: the stubbed-touch test fails on a
v1.77.0.0 scratch worktree.
Fixes #2687
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
63 lines
3.3 KiB
Bash
Executable File
63 lines
3.3 KiB
Bash
Executable File
#!/usr/bin/env bash
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# gstack-wtree — print a working-tree CONTENT fingerprint (a git tree hash).
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#
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# Builds a temp index, stages the full working tree into it (`git add -A`, so
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# .gitignore'd scratch stays out and UNTRACKED source is included), and prints
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# `git write-tree` of that index. Properties that make this the right
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# staleness fingerprint, vs `git rev-parse HEAD^{tree}`:
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#
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# - Committing identical content does NOT change the fingerprint, so a
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# record made on a dirty tree stays valid after the exact same content is
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# committed (the /ship Step 5 -> Step 16 case).
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# - Untracked new source files DO change the fingerprint, so "tests passed"
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# can't stay FRESH after a new file appears.
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# - Rebase/amend/squash that preserve content do not change it.
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#
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# Performance: the temp index is seeded by COPYING the real index (git writes
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# it atomically via rename, so the copy is a consistent snapshot). That
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# preserves the stat cache, so `git add -A` only re-hashes files whose stat
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# changed — measured 40x faster than a `read-tree HEAD` seed, which zeroes
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# stat data and forces a full re-hash of every tracked file. Both seeds
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# produce the identical write-tree hash. Fallback: `read-tree HEAD` when the
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# index copy is unavailable (fresh repo, exotic index).
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#
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# The real repo index is never touched. Staged blobs land in the object store
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# as unreachable objects and get gc'd like stash churn (note: this means the
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# CONTENT of untracked, non-ignored files enters .git/objects until gc — the
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# same property `git stash -u` has). Exit 1 outside a git repo or in a repo
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# with no commits — callers treat that as "no fingerprint".
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set -euo pipefail
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TOP=$(git rev-parse --show-toplevel 2>/dev/null) || exit 1
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# Resolve the REAL index path BEFORE exporting GIT_INDEX_FILE — with the env
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# var set, `git rev-parse --git-path index` returns the temp index itself and
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# the stat-cache seed silently self-copies into a dead fast path.
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REAL_INDEX=$(git -C "$TOP" rev-parse --git-path index 2>/dev/null || true)
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TMPIDX=$(mktemp "${TMPDIR:-/tmp}/gstack-wtree-XXXXXX")
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trap 'rm -f "$TMPIDX"' EXIT
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export GIT_INDEX_FILE="$TMPIDX"
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# Resolve relative --git-path output against the repo root.
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case "$REAL_INDEX" in
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""|/*) ;;
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*) REAL_INDEX="$TOP/$REAL_INDEX" ;;
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esac
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if [ -n "$REAL_INDEX" ] && [ -f "$REAL_INDEX" ] && cp "$REAL_INDEX" "$TMPIDX" 2>/dev/null; then
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# Carry the real index's mtime onto the copy. Git's racy-git protection
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# re-hashes any entry whose cached mtime is not older than the index file
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# itself; `cp` stamps the copy "now", which silently marks every entry
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# non-racy and lets a same-size rewrite in the same second as the original
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# `git add` keep its stale stat-cache entry — the content change vanishes
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# from the fingerprint. touch -r restores the original racy window.
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# #2687 hardening: a FAILED touch silently reopened that exact hole (the
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# copy keeps its "now" stamp). Fall through to the HEAD seed instead —
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# slower, but every entry gets re-hashed, so the fingerprint stays honest.
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if ! touch -r "$REAL_INDEX" "$TMPIDX" 2>/dev/null; then
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rm -f "$TMPIDX" 2>/dev/null || true
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git -C "$TOP" read-tree HEAD 2>/dev/null || exit 1
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fi
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else
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git -C "$TOP" read-tree HEAD 2>/dev/null || exit 1
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fi
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git -C "$TOP" add -A 2>/dev/null || exit 1
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git -C "$TOP" write-tree 2>/dev/null
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