Only limit fetch depth when the checkout is already shallow by winklemad · Pull Request #1647 · anthropics/claude-code-action

winklemad · 2026-08-14T05:14:07Z

Problem

restoreConfigFromBase fetches the PR base with --depth=1 on every PR-triggered run, and setupBranch passes --depth to each of its fetches. --depth doesn't only cap what gets downloaded: run against a checkout made with fetch-depth: 0 it also truncates the history that is already there and writes .git/shallow, so the merge base with the base branch disappears.

The damage only shows up on the realistic topology, where base has advanced since the PR branched (if the PR was cut from the current base tip there is nothing to truncate — which is why this is easy to miss locally). Reproduced with the action's exact command:

	before	after `git fetch origin main --depth=1 --no-recurse-submodules`
`git rev-parse --is-shallow-repository`	`false`	`true`
`git merge-base origin/main HEAD`	resolves	empty
`git log origin/main..HEAD`	the PR's commit	the PR's commit plus commits already merged into base
`git diff origin/main...HEAD`	the PR's diff	`fatal: origin/main...HEAD: no merge base`

Those two are exactly the commands the prompt tells Claude to run to scope its work to the PR (src/create-prompt/index.ts, and the git diff form is in the allowlist), so the action breaks its own documented workflow: silently wrong output from git log, hard failure from git diff, on every PR-triggered run in a repo that checks out with fetch-depth: 0.

Fix

Gate the flag on git rev-parse --is-shallow-repository in a small shared helper (src/github/operations/fetch-depth.ts), and use it at every --depth fetch in the action, not just the one from the issue:

restore-config.ts — the base branch fetch
branch.ts — the PR branch fetch, the fork refs/pull/N/head fetch, and both source-branch fetches (commit-signing and non-signing)

The trade-off, since the shallow fetch was deliberate (#53, for #52): on a checkout that is already shallow — the fetch-depth: 1 default, which is the case the speed-up was for — the arguments are unchanged and the saving is kept. Only a checkout that already has full history now fetches without a depth limit, which is what asking for fetch-depth: 0 means. If git rev-parse can't answer (not a repo, or a git too old for the flag) the helper assumes full history: over-fetching is recoverable, truncating history isn't.

Tests

test/restore-config.test.ts — regression test on the diverged topology (base advances after the PR branch is cut): asserts the repo is still not shallow after restoreConfigFromBase, the merge base still resolves to the same commit, origin/main..HEAD is still just the PR's commit, and the three-dot diff still works. Fails on main.
test/fetch-depth.test.ts — setupBranch keeps the full history of a complete checkout for both use_commit_signing values (also fails on main), plus coverage that an already shallow checkout still gets --depth and a complete one doesn't.

bun test 915 pass / 0 fail (910 before this change), bun run typecheck and bun run format:check clean.

restoreConfigFromBase and setupBranch pass --depth to every git fetch. On a checkout made with fetch-depth: 0 that does not just cap the download: it truncates the history already present and marks the repository shallow, which drops the merge base with the base branch. `git log origin/<base>..HEAD` then silently includes commits that are already merged, and `git diff origin/<base>...HEAD` fails with "no merge base" — the two commands the prompt tells Claude to run to scope its work to the PR. Gate the flag on `git rev-parse --is-shallow-repository`, so a checkout that is already shallow (the fetch-depth: 1 default) keeps the same depth behaviour and the fetch savings it was added for, while a full checkout stays full. Fixes anthropics#1642

ashwin-ant approved these changes Aug 14, 2026

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ashwin-ant merged commit ed186be into anthropics:main Aug 14, 2026
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ashwin-ant mentioned this pull request Aug 14, 2026

ci: skip Claude-backed test jobs on fork PRs #1655

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rajanpanth mentioned this pull request Aug 15, 2026

fix: preserve full checkout when restoring trusted PR config #1653

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github-actions Bot mentioned this pull request Aug 22, 2026

chore(deps): update anthropics/claude-code-action action to v1.0.194 lacolaco/zenn#403

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clanker-claude Bot mentioned this pull request Aug 31, 2026

ci(github-action): update action anthropics/claude-code-action ( be7b93b ➔ a874e9e ) mrdynamo/home-ops#2875

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Only limit fetch depth when the checkout is already shallow - #1647

Only limit fetch depth when the checkout is already shallow#1647
ashwin-ant merged 1 commit into
anthropics:mainfrom
winklemad:fix/fetch-depth-preserve-full-history

winklemad commented Aug 14, 2026

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winklemad commented Aug 14, 2026

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