fix: make --dry-run correctly report formatting issues - #257
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Problem: --dry-run mode always returned 0, never blocking commits even when clang-format detected unformatted files. This was caused by: 1. run_clang_format() replacing the actual exit code with -1 2. main() converting -1 back to 0 This contradicted user intuition (dry-run should fail if formatting needs fixing) and differed from mirrors-clang-format's behavior. Fix: - Remove the special -1 code path entirely - Auto-inject --Werror when --dry-run is present, so clang-format returns non-zero when formatting changes are needed (mirrors-clang- format behavior) - Pass through the real exit code from clang-format Tests updated: dry-run on unformatted file expects 1, on formatted file expects 0.
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shenxianpeng
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## main #257 +/- ##
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## Why cpp-linter-hooks already gets more Google traffic than the action (52 of its 288 repository views in the last 14 days came from Google, against 21 for cpp-linter-action), so people are searching for "clang-format pre-commit hook". The site has no page for that query. This is the second how-to written around a search term, after #62; the two PRs are independent. ## What's in this PR One new post in the Guides category: **Set up a clang-format pre-commit hook for C and C++** (`docs/blog/posts/2026-09-20-clang-format-pre-commit-hook.md`), published at `/blog/2026/09/20/clang-format-pre-commit-hook/` (explicit `slug`, plus a meta `description`). 1. A starter `.clang-format`. 2. Installing pre-commit and adding the hook; `rev` is the hook version, `--version` is the clang-format version (`21` resolves to the newest 21.x wheel, a full version pins it exactly). 3. What the first commit looks like, and why "Failed" means the files were fixed. 4. Formatting only your own code: `exclude`, a `DisableFormat` `.clang-format` in the vendored directory, and `types_or` for CUDA and Protobuf. 5. Existing code bases: reformat once with `.git-blame-ignore-revs`, or format as you go; `git clang-format` mentioned for changed-lines-only. 6. Enforcing the same configuration in CI with `pre-commit run --all-files --show-diff-on-failure`, or review suggestions from cpp-linter-action with `format-review`. 7. A troubleshooting table. 8. When to add the clang-tidy hook. ## Checks - Every command and output in the post was run in a scratch git repository with `rev: v1.6.0` and `--version=21` (resolved to clang-format 21.1.8): the blocked commit and the retry, `exclude`, the per-directory `DisableFormat`, `.cu` and `.proto` formatting via `types_or`, `SKIP=clang-format`, the CI output (pasted verbatim) and `blame.ignoreRevsFile`. - The compile database auto-detection mentioned in the last section was checked against `clang_tidy.py` at v1.6.0. - `mkdocs build --strict` passes locally, and the repository's pre-commit hooks pass on the new file. ## Notes - The post does not recommend `--dry-run`. With the released v1.6.0 the hook reports "Passed" for an unformatted file when `--dry-run` is set, with or without `--Werror`; the fix (cpp-linter/cpp-linter-hooks#257) is on `main` but not in a release yet. Once it is released, a check-only variant can be added to step 6. - There is no link to the clang-tidy guide from #62, because that page does not exist on `main` yet and the strict build would fail. The two posts can be cross-linked in a small follow-up once both are merged.
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Problem: --dry-run mode always returned 0, never blocking commits even when clang-format detected unformatted files. This was caused by:
This contradicted user intuition (dry-run should fail if formatting needs fixing) and differed from mirrors-clang-format's behavior.
Fix:
Tests updated: dry-run on unformatted file expects 1, on formatted file expects 0.
Summary
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