Enable capi when running CPython tests by bschoenmaeckers · Pull Request #9270 · RustPython/RustPython

bschoenmaeckers · 2026-10-21T08:14:15Z

Summary by CodeRabbit

Bug Fixes
- Improved Windows builds with the C API enabled by making required CPython C API symbols available.
- Builds now report a clear failure if the C API export definitions cannot be read.
Build Improvements
- Updated automated release and cache-building configurations to enable the C API feature, making it available consistently across these build workflows.

coderabbitai · 2026-10-21T08:14:23Z

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Walkthrough

The release and cache-building workflows now enable the capi feature. On Windows, build.rs reads a C API export manifest and passes symbol and definition-file arguments to the linker.

Changes: C API Windows exports

Layer / File(s)	Summary
Enable C API in build workflows `.github/workflows/ci.yaml`, `.github/workflows/update-caches.yml`	The release build and cache-building Cargo commands enable the `capi` feature.
Configure Windows C API exports `rustpython-capi-exports.def`, `build.rs`	The manifest lists 532 C API symbols. When Windows builds enable `capi`, the build script reads the manifest, emits `/INCLUDE:` arguments for its nonblank symbol lines, and passes the file with `/DEF:`. A read failure stops the build script.

Priority: Low

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

Change: Other

Sequence Diagram(s)

sequenceDiagram
  participant Cargo
  participant BuildScript as build.rs
  participant Manifest as rustpython-capi-exports.def
  participant Linker
  Cargo->>BuildScript: Run Windows build with capi enabled
  BuildScript->>Manifest: Read symbol definitions
  BuildScript->>Linker: Emit /INCLUDE arguments and /DEF manifest

Possibly related PRs

RustPython/RustPython#9407: Adds the tp_new C API slot and wires C constructors into the C API, which shares the C API build and exported-symbol surface.
RustPython/RustPython#9409: Adds PyOS_snprintf and PyOS_vsnprintf to the C API symbol surface built and exported here.

Suggested reviewers: shaharnaveh

Merge Risk: Low · up to 64f71

C API builds can fail on Windows GNU and 32-bit MSVC targets. These are bounded compatibility issues outside the demonstrated CI targets; address them or explicitly accept those target limitations before merging.

Pre-merge checks: 5

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly describes the primary change: enabling the `capi` feature for CPython test builds. The workflow, cache, linker, and export changes support this objective.
Docstring Coverage		Docstring coverage is inconclusive: files from earlier reviews still need to be rechecked within the check's analysis limits. Not blocking.
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.

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github-actions · 2026-10-21T08:15:21Z

📦 Library Dependencies

The following Lib/ modules were modified. Here are their dependencies:

[x] lib: cpython/Lib/threading.py
[x] lib: cpython/Lib/_threading_local.py
[x] test: cpython/Lib/test/test_threading.py (TODO: 4)
[x] test: cpython/Lib/test/test_threadedtempfile.py
[x] test: cpython/Lib/test/test_threading_local.py

dependencies:

threading

dependent tests: (194 tests)

[x] test: cpython/Lib/test/test_frame.py (TODO: 1)

dependencies:

dependent tests: (no tests depend on frame)

[x] lib: cpython/Lib/ctypes
[ ] test: cpython/Lib/test/test_ctypes (TODO: 6)
[ ] test: cpython/Lib/test/test_stable_abi_ctypes.py

dependencies:

ctypes

dependent tests: (37 tests)

ctypes: test_android test_buffer test_bytes test_code test_codecs test_ctypes test_genericalias test_ntpath test_os test_ssl test_venv
- platform: test__locale test__osx_support test_asyncio test_baseexception test_builtin test_calendar test_cmath test_fcntl test_math test_mimetypes test_os test_platform test_regrtest test_shutil test_socket test_strptime test_sysconfig test_time test_tkinter test_winreg test_wsgiref
  - profiling.sampling.gecko_collector: test_profiling
  - profiling.sampling.heatmap_collector: test_profiling
  - pydoc: test_enum test_pydoc
- webbrowser: test_webbrowser

Legend:

[+] path exists in CPython
[x] up-to-date, [ ] outdated

codspeed · 2026-10-21T09:24:17Z

Merging this PR will not alter performance

✅ 62 untouched benchmarks
⏩ 4 skipped benchmarks¹

_{Comparing bschoenmaeckers:c-api-python-tests (3196c44) with main (0b0a360)}

4 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. ↩

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Actionable comments posted: 5

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Inline comments:
Review comments at @build.rs:
- Line 49: Update the build script’s rerun-if-changed setup to also emit a
directive for the capi_src directory, alongside the per-file println! call, so
Cargo detects newly added C API source files.
- Around line 33-35: Update the capi_enabled branch around
export_capi_symbols_for_windows_exe so any export-generation error propagates
from the build script and causes a nonzero exit. Remove the warning-only
handling while preserving the successful path when generation completes.
- Line 33: Move the capi_enabled check that calls
export_capi_symbols_for_windows_exe() to the beginning of the Windows branch,
before the logo.ico existence handling and any early return. Preserve its
existing warning behavior, and remove the later duplicate call so C API exports
are generated independently of icon embedding.
- Line 64: Restrict C API export generation in the Windows branch to MSVC
targets by reading CARGO_CFG_TARGET_ENV and requiring it to equal "msvc"
alongside capi_enabled before calling export_capi_symbols_for_windows_exe.
Preserve the existing Windows resource handling for GNU targets.
- Around line 124-169: Update the Windows symbol-collection flow to include
names from define_py_check! invocations, whose generated extern functions are
not detected by extract_no_mangle_symbols. Add a dedicated extractor for both
normal and exact forms, parse the function name, insert it into the shared
BTreeSet, and invoke it alongside extract_define_exception_statics_symbols
before generating exports and /INCLUDE arguments.

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⛔ Files ignored due to path filters: 3

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.github/workflows/ci.yaml
.github/workflows/update-caches.yml
build.rs

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chatgpt-codex-connector · 2026-10-21T16:03:40Z

      # Keep features in sync with update-caches.yml CARGO_ARGS.
      - name: build rustpython
-        run: cargo build --locked --release --verbose --features=threading,jit ${{ env.CARGO_ARGS }}
+        run: cargo build --locked --release --verbose --features=threading,jit,capi ${{ env.CARGO_ARGS }}


Preserve xfails for builds without the C-API

For the documented default-feature test command, the three newly un-xfailed tests still have no C-API: this line enables capi only for the Run snippets and cpython tests release binary, while capi is absent from Cargo.toml's default feature list and src/lib.rs takes the non-CAPI path without it. Consequently a normal cargo run --release -- -m test test_ctypes.test_python_api (and likewise test_frame or test_threading) now fails at ctypes.pythonapi symbol lookup; make the expectation conditional on C-API availability or enable the feature in every supported test build.

AGENTS.md reference: AGENTS.md:L280-L282

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chatgpt-codex-connector · 2026-10-21T16:03:45Z

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chatgpt-codex-connector · 2026-10-21T16:33:01Z

+fn export_capi_symbols_for_windows_exe() -> Result<(), String> {
+    let mut files = Vec::new();
+    let mut symbols = BTreeSet::new();
+    let capi_src = Path::new("crates").join("capi").join("src");


Generate exports without workspace-only sources

For a published-crate build with the capi feature on Windows, this generator is unavailable: Cargo.toml:4 packages only LICENSE, Cargo.toml, and src/**/*.rs, so Cargo omits build.rs entirely (and the separately published rustpython-capi dependency is not available at crates/capi/src). The resulting executable receives neither the generated .def file nor the /INCLUDE arguments, leaving ctypes.pythonapi unable to resolve the C-API symbols despite enabling the feature; package a source-independent export list or generate it from within rustpython-capi instead of relying on the workspace layout.

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youknowone · 2026-10-22T13:07:53Z

+    });
+}
+
+fn extract_no_mangle_symbols(content: &str, symbols: &mut BTreeSet<String>) {


I am not sure this is a good idea. do you have alternative plans?

Not sure. I do not have a windows machine by hand, so testing this was quite hard. We could instead define a static list somewhere in the repo?

I've pushed 3196c44 instead. What do you think? In the future there may be automatic options like export-executable-symbols. But I'm not sure this actually does what we need.

this is looking better than before. I also think expor-executable-symbols is the correct thing. what if we require nightly(or the env technique we must regard not really exist in stable) only for windows+msvc build?

what if we require nightly(or the env technique we must regard not really exist in stable) only for windows+msvc build?

Do you think its acceptable to run the Run snippets and cpython tests on nightly for windows? This makes the CI diverge from the other platforms.

let's keep other windows CI use stable, and nightly only for windows+capi. we currrently don't have nightly CI, so it will be useful not to break nightly build too

I think we should move forward with the static file. Until other stable options are available. This keeps the setup simple.

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Try fix windows 2 Try fix windows 3 Try fix windows 4 Try fix windows 5

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Inline comments:
Review comments at @rustpython-capi-exports.def:
- Line 2: Restrict the Windows C-API export block in main to MSVC targets so GNU
Windows targets do not receive MSVC-specific linker arguments. Read the target
environment and call export_capi_symbols_for_windows_exe only when C-API is
enabled and the target environment is msvc.
- Line 4: Update the export handling in build.rs to prefix /INCLUDE names with
an underscore only when the target architecture is x86, preserving the existing
names for other architectures. Leave rustpython-capi-exports.def unchanged.

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bschoenmaeckers changed the title ~~Enable capi when testing CPython tests~~ Enable capi when running CPython tests Oct 21, 2026

bschoenmaeckers force-pushed the c-api-python-tests branch from 504e529 to 154c38f Compare October 21, 2026 08:54

bschoenmaeckers force-pushed the c-api-python-tests branch 6 times, most recently from b5dbe1e to 8c83faf Compare October 21, 2026 14:52

bschoenmaeckers marked this pull request as ready for review October 21, 2026 15:47

bschoenmaeckers force-pushed the c-api-python-tests branch from 8c83faf to 98bd344 Compare October 21, 2026 15:53

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bschoenmaeckers force-pushed the c-api-python-tests branch from ec082f7 to 3196c44 Compare October 22, 2026 13:26

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Comment thread build.rs

youknowone mentioned this pull request Oct 23, 2026

Add a _testcapi module #9143

Open

youknowdot mentioned this pull request Oct 26, 2026

Run C API Clippy with its crate-local PyO3 configuration #9385

Draft

bschoenmaeckers added 5 commits October 28, 2026 09:01

Enable capi when testing CPython tests

3592272

Try fix windows exports

fcd5ca3

Try fix windows 2 Try fix windows 3 Try fix windows 4 Try fix windows 5

Review

9435491

Use static export list instead

1567808

Add PyOS_snprintf/PyOS_vsnprintf

64f715d

bschoenmaeckers force-pushed the c-api-python-tests branch from 3196c44 to 64f715d Compare October 28, 2026 08:03

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