fix: make --dry-run correctly report formatting issues

[shenxianpeng]

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.

Summary

Related Issues

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Review details

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📥 Commits

Reviewing files that changed from the base of the PR and between 21f53f4 and 1206023.

📒 Files selected for processing (2)

• cpp_linter_hooks/clang_format.py
• tests/test_clang_format.py

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.51%. Comparing base (21f53f4) to head (1206023).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #257   +/-   ##
=======================================
  Coverage   97.51%   97.51%           
=======================================
  Files           3        3           
  Lines         241      241           
=======================================
  Hits          235      235           
  Misses          6        6           

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[codspeed-hq]

Merging this PR will not alter performance

✅ 90 untouched benchmarks
🆕 2 new benchmarks
⏩ 54 skipped benchmarks¹

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
🆕	test_run_clang_format_dry_run_formatted	N/A	840.3 µs	N/A
🆕	test_run_clang_format_dry_run_unformatted	N/A	891.1 µs	N/A

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_{Comparing bugfix/dry-run-return-code (1206023) with main (12c3973)²}

Footnotes

1. 54 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on main (21f53f4) during the generation of this report, so 12c3973 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩