Add PyOS_vsnprintf & PyOS_snprintf to the capi - #9409

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Recent review info

Run configuration

• Source mode: Auto
• Repository: RustPython/RustPython
• Branch: main
• File: .coderabbit.yml
• Commit: b25ab5e
• Layers: Repository YAML
• Review profile: CHILL
• Plan: Advanced
• Run ID: 99cf0023-9a74-4848-9522-84b5dbe4a876

Commits

Reviewing files that changed from the base of the PR and between b25ab5e and 5b6a5cc.

Files selected for processing: 1

• crates/capi/src/pyerrors.rs

Included review availability: This review used your included allowance. Your plan provides up to 10 included reviews per hour; 8 remain after this review.

This change adds PyOS_snprintf and PyOS_vsnprintf to the C API. The variadic function forwards its arguments to the va_list function, which calls vsnprintf when the size is within the supported limit.

Changes: Formatted string output API

Layer / File(s)	Summary
Add snprintf wrappers crates/capi/src/pyerrors.rs	Adds PyOS_snprintf and PyOS_vsnprintf. The latter returns -666 when size exceeds c_int::MAX - 1. When size > 0 and the destination is non-null, it writes a terminating NUL at str[size - 1].

Priority: Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Suggested reviewers: youknowone

Merge Risk: Minimal · up to 5b6a5

No merge-blocking risk is established; normal build and test checks remain appropriate.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within survi…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title names the two C APIs the PR adds, PyOS_vsnprintf and PyOS_snprintf, and the raw summary confirms both are added to crates/capi/src/pyerrors.rs. The title matches the main change and the comm…
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Title check

Explanation

The title names the two C APIs the PR adds, PyOS_vsnprintf and PyOS_snprintf, and the raw summary confirms both are added to crates/capi/src/pyerrors.rs. The title matches the main change and the commit message.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 2 functions across 1 files.

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

🧪 Generate unit tests (beta)

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