use posix error messages under 127 by youknowone · Pull Request #6420 · RustPython/RustPython

youknowone

Walkthrough

Adds platform-conditional message construction in ToPyException for std::io::Error: Windows attempts to use the C runtime strerror for POSIX errno (1–127) with fallbacks to self.to_string() or "Unknown error"; Unix uses strerror(errno) when available; other targets fall back to the original error string.

Changes

Cohort / File(s)	Summary
IO errno message handling `crates/vm/src/stdlib/io.rs`	Adds platform-conditional logic in `ToPyException` for `std::io::Error`. On Windows, attempts to build messages via the C runtime `strerror` for POSIX `errno` (1–127) and falls back to `self.to_string()` or `"Unknown error"`; on Unix uses `strerror(errno)` when available; other targets use the original string.

Estimated code review effort

🎯 4 (Complex) | ⏱️ ~45 minutes

Inspect platform-specific FFI calls to the C runtime (strerror) and safety around pointers and encoding.
Verify correct errno range checks (1–127) and the "Unknown error" fallback logic on Windows.
Check conditional compilation for Unix, Windows, and other targets and run cross-platform tests where possible.

Possibly related PRs

WindowsError #6333 — Also modifies Windows-specific error handling and message construction for OSError/IO errors; related at the code-level for errno/winerror and strerror usage.

Poem

🐰 I nibble at C strings late at night,
Hopping through errno by dim moonlight,
On Windows I peek where strerror hides,
On Unix I listen where the old echo bides,
Carrots, crumbs, and clearer error sights 🥕

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	You can run `@coderabbitai generate docstrings` to improve docstring coverage.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'use posix error messages under 127' accurately describes the main change: implementing POSIX error message handling for errno values under 127 in the ToPyException implementation for std::io::Error.

✨ Finishing touches

📝 Generate docstrings

🧪 Generate unit tests (beta)

Create PR with unit tests
Post copyable unit tests in a comment

📜 Recent review details

Configuration used: Path: .coderabbit.yml

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between b093b19 and 786a65e.

⛔ Files ignored due to path filters (3)

Lib/test/test_argparse.py is excluded by !Lib/**
Lib/test/test_py_compile.py is excluded by !Lib/**
Lib/test/test_subprocess.py is excluded by !Lib/**

📒 Files selected for processing (1)

crates/vm/src/stdlib/io.rs (1 hunks)

🚧 Files skipped from review as they are similar to previous changes (1)

crates/vm/src/stdlib/io.rs

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