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youknowone merged 2 commits into from
Jun 1, 2026
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Add agent skill for adding c-api functions #8001

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Add agent skill
bschoenmaeckers Jun 1, 2026
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abi3/abi3t only
bschoenmaeckers Jun 1, 2026
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60 changes: 60 additions & 0 deletions .agents/skills/rustpython-capi-expansion/SKILL.md
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---
name: rustpython-capi-expansion
description: Implement missing RustPython C-API functions in crates/capi using the pyo3-ffi header split mapping (`pyo3-ffi/src/*.rs`, mirroring CPython C API headers). Use this whenever the user asks to add or port C-API functions (for example from setobject.h, dictobject.h, unicodeobject.h) or add capi tests.
---

# RustPython C-API Expansion

Use this workflow for adding missing C-API functions to RustPython.

## Source of truth for target files

- Use this mapping source: `pyo3-ffi/src/*.rs`, which mirrors the CPython header split used by the C API.

@coderabbitai coderabbitai Bot Jun 1, 2026

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⚠️ Potential issue | 🟠 Major | ⚡ Quick win

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
# Check if pyo3-ffi exists in the repository or is a known external dependency

# Check if pyo3-ffi is a local path in the repository
if fd -t d 'pyo3-ffi' .; then
  echo "Found pyo3-ffi directory in repository"
  fd -t f -e rs . pyo3-ffi/src/ | head -5
else
  echo "pyo3-ffi not found as local directory"
fi

# Check if pyo3-ffi is referenced in Cargo.toml files
rg -n 'pyo3-ffi' -g 'Cargo.toml' -C 2

Repository: RustPython/RustPython

Length of output: 223

Fix pyo3-ffi/src/*.rs reference in SKILL.md (line 12)

  • pyo3-ffi/src/*.rs is not reachable via a local pyo3-ffi/src directory in this repo checkout (the follow-up search path pyo3-ffi/src/ is missing).
  • Since pyo3-ffi is a crate dependency rather than vendored here, update the skill to tell agents where to obtain the pyo3-ffi sources that correspond to the Cargo.lock version (e.g., the Cargo registry checkout / cargo vendor / docs.rs), so the CPython header-split mapping is actually accessible.
🤖 Prompt for AI Agents 
Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In @.agents/skills/rustpython-capi-expansion/SKILL.md at line 12, The SKILL.md
reference to pyo3-ffi/src/*.rs is incorrect because pyo3-ffi is a crate
dependency not vendored here; update the SKILL.md instruction (line referencing
`pyo3-ffi/src/*.rs`) to tell agents how to obtain the exact pyo3-ffi sources
that match the repo’s Cargo.lock (e.g., instruct to fetch the crate from the
Cargo registry with the version from Cargo.lock, use `cargo vendor` to vendor
pyo3-ffi into the workspace, or point to the matching docs.rs/crates.io
release), and include which file pattern to look for (`pyo3-ffi/src/*.rs`) once
the crate sources are fetched so the CPython header-split mapping becomes
accessible.

- Map requested header APIs to `crates/capi/src/<header_basename>.rs` using that split. Examples:
- `setobject.h` -> `crates/capi/src/setobject.rs`
- `dictobject.h` -> `crates/capi/src/dictobject.rs`
- `unicodeobject.h` -> `crates/capi/src/unicodeobject.rs`
- Do not invent alternate target modules when the header split implies a direct target.
- If the target file is not present yet, create it and wire it in `crates/capi/src/lib.rs`.

## Implementation workflow

1. Identify requested missing APIs from the user request and their originating C API header.
2. Open nearby capi modules in `crates/capi/src/` and follow existing style and patterns.
3. Implement only the requested functions in the mapped target file.
4. Keep behavior aligned with CPython C-API contracts.
5. Prefer using existing `rustpython-vm` functionality as much as possible instead of re-implementing behavior in capi.
6. If a needed `rustpython-vm` helper exists but is private, make it public with a minimal, focused visibility change.
7. Prefer direct contract assumptions over defensive null checks unless required by the established local style.
8. Add basic tests only; do not overfit with very specific edge-case clutter.
9. In tests, use `pyo3` only as a safe wrapper over the API. Avoid raw pointer-heavy direct FFI-style tests.
10. Run tests from `crates/capi`.

## Testing rules

- Run test commands with working directory set to `crates/capi`.
- Prefer targeted tests first (module/function filter), then broader capi tests if needed.
- Keep test names concise (no required `test_` prefix).

## Style rules

- Follow existing RustPython capi coding style in neighboring files.
- Reuse `rustpython-vm` methods and types first; avoid duplicating VM logic in capi wrappers.
- When exposing previously private VM helpers, keep the API surface minimal and avoid unrelated refactors.
- Only expose and implement ABI-stable C-API surface needed for `abi3` / `abi3t`.
- Add comments only when they explain non-obvious behavior.
- Keep edits minimal and focused on requested API expansion.

## Completion checklist

- [ ] All requested functions implemented in mapped target file.
- [ ] New module exported in `crates/capi/src/lib.rs` when applicable.
- [ ] Basic safe-wrapper `pyo3` tests added/updated.
- [ ] Tests executed from `crates/capi` and passing for changed area.
- [ ] Final response includes changed file paths and test command summary.

## Example prompts this skill should handle

- "Implement these missing functions from `dictobject.h`."
- "Add `setobject.h` C-API functions in RustPython and include basic tests."
- "Port the listed `unicodeobject.h` APIs in capi, follow existing style, and run tests from `crates/capi`."
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