Add free-threaded Python support

[messense]

Implementation details:

• Free-threaded support is determined by the Py_GIL_DISABLED build flag for runnable Python interpreters
• We also accept python3.13t when cross compiling

Closes #2298
Closes #2315

[messense]

This change is part of the following stack:

• Add free-threaded Python support #2310 ◀

_{Change managed by git-spice.}

[davidhewitt]

For testing it's possible to use https://github.com/Quansight-Labs/setup-python as a drop-in replacement for the GitHub one

Copilot reviewed 3 out of 3 changed files in this pull request and generated no suggestions.

Comments skipped due to low confidence (1)

src/python_interpreter/config.rs:131

• The handling of abiflags for free-threaded Python on Windows is incomplete. This could lead to unexpected behavior if free-threaded Python is used on Windows.

// FIXME: windows abiflags for free-threaded python?

[ngoldbaum]

Happy to help with this if needed. The windows free-threaded packaging situation is "fun".

[messense]

Happy to help with this if needed.

Thanks, feel free to send PR to this branch!

[ngoldbaum]

It looks like a few of the tests hardcode using abi3:

○  rg "abi3" **/Cargo.toml
pyo3-pure/Cargo.toml
10:pyo3 = { version = "0.22.0", features = ["abi3-py37", "extension-module", "generate-import-lib"] }

pyo3-abi3-without-version/Cargo.toml
2:name = "pyo3-abi3-without-version"
8:pyo3 = { version = "0.22.4", features = ["abi3", "extension-module"] }
11:name = "pyo3_abi3_without_version"

workspace-inverted-order/path-dep-with-root/Cargo.toml
13:pyo3 = { version = "0.22.5", features = ["abi3", "abi3-py38", "extension-module"] }

pyo3-ffi-pure/Cargo.toml
7:pyo3-ffi = { version = "0.18.1", features = ["abi3-py37", "extension-module"] }

Since free-threading and abi3 are incompatible, would it be better to skip over the tests that use these crates? For the ones that are testing whether the limited api support is working correctly I think skipping them makes sense, but some of these seem to be more generic integration tests for maturin that happen to use the limited API.

I don't see an easy way to optionally turn on and off the abi3 feature in the test crates. Am I missing something? If not, any guidance?

[davidhewitt]

We should probably try to support this case because cryptography probably hard-codes the abi3 build in the same way. It's useful to do that because then the whole system limits you to the limited API.

My gut says that it'd be good enough for now if Py_GIL_DISABLED being set caused pyo3-build-config to no-op the whole lot of abi3 features. So maybe there's a PyO3 fix required here? 🤔

[ngoldbaum]

My gut says that it'd be good enough for now if Py_GIL_DISABLED being set caused pyo3-build-config to no-op the whole lot of abi3 features. So maybe there's a PyO3 fix required here?

Hmm, that's sort of in the vein of PyO3/pyo3#4719, but maybe what I'm doing there making more things hard errors is bad and it would be better to warn and just turn off limited API and set the ABI to Py_3_13 if someone is trying to build for the free-threaded ABI but asks for an earlier ABI.

[alex]

We should probably try to support this case because cryptography probably hard-codes the abi3 build in the same way. It's useful to do that because then the whole system limits you to the limited API.

We have a convoluted setup where Cargo.toml specifies the abi3 feature, pyproject.toml specifies the pyo3/abi3-py37 feature, and then some individual wheel building jobs specify higher abi3 ABIs.

[davidhewitt]

👍 It seems to me that we probably don't want cryptography to have to remove abi3 feature from Cargo.toml to build against the freethreaded build, so silently overriding (like we do for PyPy & Graalpy) seems more correct. I guess we can probably also make that work for the abi3-py37 too, I'll check how that works...

[davidhewitt]

Yep, if I add abi3-py37 to Cargo.toml and then try to build with PyPy, the build succeeds (with a warning about PyPy not supporting abi3), I guess we should match here.

[ngoldbaum]

It looks like three of the crates use old PyO3 APIs and need to be updated:

test-crates/sdist_with_target_path_dep/src/lib.rs
18:    let pool = ::pyo3::GILPool::new();
116:    let pool = ::pyo3::GILPool::new();

test-crates/lib_with_path_dep/src/lib.rs
18:    let pool = ::pyo3::GILPool::new();
116:    let pool = ::pyo3::GILPool::new();

test-crates/sdist_with_path_dep/src/lib.rs
18:    let pool = ::pyo3::GILPool::new();
116:    let pool = ::pyo3::GILPool::new();

Other errors from trying to build one of these crates:

   Compiling sdist_with_path_dep v0.1.0 (/Users/goldbaum/Documents/maturin/test-crates/sdist_with_path_dep)
error[E0432]: unresolved import `pyo3::derive_utils`
   --> src/lib.rs:113:15
    |
113 |     use pyo3::derive_utils::ModuleDef;
    |               ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `GILPool` in `pyo3`
  --> src/lib.rs:18:24
   |
18 |     let pool = ::pyo3::GILPool::new();
   |                        ^^^^^^^ could not find `GILPool` in `pyo3`

error[E0433]: failed to resolve: could not find `derive_utils` in `pyo3`
  --> src/lib.rs:26:47
   |
26 |                 const PARAMS: &'static [pyo3::derive_utils::ParamDescription] = &[
   |                                               ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `derive_utils` in `pyo3`
  --> src/lib.rs:27:27
   |
27 |                     pyo3::derive_utils::ParamDescription {
   |                           ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `derive_utils` in `pyo3`
  --> src/lib.rs:32:27
   |
32 |                     pyo3::derive_utils::ParamDescription {
   |                           ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `derive_utils` in `pyo3`
  --> src/lib.rs:41:46
   |
41 |                 let (_args, _kwargs) = pyo3::derive_utils::parse_fn_args(
   |                                              ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `derive_utils` in `pyo3`
  --> src/lib.rs:53:44
   |
53 |                         .map_err(|e| pyo3::derive_utils::argument_extraction_error(_py, "x", e))?,
   |                                            ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `derive_utils` in `pyo3`
  --> src/lib.rs:61:44
   |
61 |                         .map_err(|e| pyo3::derive_utils::argument_extraction_error(_py, "y", e))?,
   |                                            ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `callback` in `pyo3`
  --> src/lib.rs:85:17
   |
85 |         ::pyo3::callback::callback_error()
   |                 ^^^^^^^^ could not find `callback` in `pyo3`

error[E0433]: failed to resolve: could not find `derive_utils` in `pyo3`
  --> src/lib.rs:89:27
   |
89 |     args: impl Into<pyo3::derive_utils::PyFunctionArguments<'a>>,
   |                           ^^^^^^^^^^^^ could not find `derive_utils` in `pyo3`

error[E0433]: failed to resolve: could not find `GILPool` in `pyo3`
   --> src/lib.rs:116:24
    |
116 |     let pool = ::pyo3::GILPool::new();
    |                        ^^^^^^^ could not find `GILPool` in `pyo3`

error[E0433]: failed to resolve: could not find `callback` in `pyo3`
   --> src/lib.rs:137:17
    |
137 |         ::pyo3::callback::callback_error()
    |                 ^^^^^^^^ could not find `callback` in `pyo3`

error[E0433]: failed to resolve: could not find `callback` in `pyo3`
  --> src/lib.rs:22:17
   |
22 |         ::pyo3::callback::convert(_py, {
   |                 ^^^^^^^^ could not find `callback` in `pyo3`

error[E0433]: failed to resolve: could not find `callback` in `pyo3`
   --> src/lib.rs:120:17
    |
120 |         ::pyo3::callback::convert(_py, MODULE_DEF.make_module("", pyo3_pure))
    |                 ^^^^^^^^ could not find `callback` in `pyo3`

warning: use of deprecated type alias `pyo3::PyMethodType`: PyO3 implementation detail
  --> src/lib.rs:97:22
   |
97 |         pyo3::class::PyMethodType::PyCFunctionWithKeywords(__pyo3_raw_add),
   |                      ^^^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

error[E0061]: this function takes 3 arguments but 5 arguments were supplied
   --> src/lib.rs:94:5
    |
94  |     pyo3::types::PyCFunction::internal_new(
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
95  |         name,
    |         ---- expected `Python<'_>`, found `&CStr`
96  |         doc,
    |         --- expected `&PyMethodDef`, found `&CStr`
97  |         pyo3::class::PyMethodType::PyCFunctionWithKeywords(__pyo3_raw_add),
98  |         pyo3::ffi::METH_VARARGS | pyo3::ffi::METH_KEYWORDS,
    |         -------------------------------------------------- unexpected argument #4 of type `i32`
99  |         args.into(),
    |         ----------- unexpected argument #5
    |
    = note: expected reference `&pymethods::PyMethodDef`
               found reference `&CStr`
note: expected `Option<&Bound<'_, ...>>`, found `PyMethodType`
   --> src/lib.rs:97:9
    |
97  |         pyo3::class::PyMethodType::PyCFunctionWithKeywords(__pyo3_raw_add),
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    = note: expected enum `Option<&pyo3::Bound<'_, pyo3::types::PyModule>>`
               found enum `PyMethodType`
note: associated function defined here
   --> /Users/goldbaum/Documents/pyo3/src/types/function.rs:151:12
    |
151 |     pub fn internal_new<'py>(
    |            ^^^^^^^^^^^^
help: remove the extra arguments
    |
95  ~         /* Python<'_> */,
96  ~         /* &pymethods::PyMethodDef */,
97  ~         /* Option<&pyo3::Bound<'_, pyo3::types::PyModule>> */,
    |

error[E0308]: mismatched types
   --> src/lib.rs:94:5
    |
90  |   ) -> pyo3::PyResult<&'a pyo3::types::PyCFunction> {
    |        -------------------------------------------- expected `Result<&'a pyo3::types::PyCFunction, PyErr>` because of return type
...
94  | /     pyo3::types::PyCFunction::internal_new(
95  | |         name,
96  | |         doc,
97  | |         pyo3::class::PyMethodType::PyCFunctionWithKeywords(__pyo3_raw_add),
98  | |         pyo3::ffi::METH_VARARGS | pyo3::ffi::METH_KEYWORDS,
99  | |         args.into(),
100 | |     )
    | |_____^ expected `Result<&PyCFunction, PyErr>`, found `Result<Bound<'_, ...>, ...>`
    |
    = note: expected enum `Result<&'a pyo3::types::PyCFunction, _>`
               found enum `Result<pyo3::Bound<'_, pyo3::types::PyCFunction, >, _>`

error[E0277]: the trait bound `Result<&pyo3::types::PyCFunction, PyErr>: IntoPyCallbackOutput<'_, Py<PyAny>>` is not satisfied
   --> src/lib.rs:104:7
    |
104 |     m.add_wrapped(&__pyo3_get_function_add)?;
    |       ^^^^^^^^^^^ the trait `IntoPyCallbackOutput<'_, Py<PyAny>>` is not implemented for `Result<&pyo3::types::PyCFunction, PyErr>`
    |
    = help: the trait `IntoPyCallbackOutput<'py, U>` is implemented for `Result<T, E>`
note: required by a bound in `add_wrapped`
   --> /Users/goldbaum/Documents/pyo3/src/types/module.rs:311:12
    |
309 |     fn add_wrapped<T>(&self, wrapper: &impl Fn(Python<'py>) -> T) -> PyResult<()>
    |        ----------- required by a bound in this associated function
310 |     where
311 |         T: IntoPyCallbackOutput<'py, PyObject>;
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `PyModuleMethods::add_wrapped`

Some errors have detailed explanations: E0061, E0277, E0308, E0432, E0433.
For more information about an error, try `rustc --explain E0061`.
warning: `sdist_with_path_dep` (lib) generated 1 warning
error: could not compile `sdist_with_path_dep` (lib) due to 17 previous errors; 1 warning emitted

I'm confused why the update to PyO3 0.23 last week didn't break tests using these crates on CI.

Copilot reviewed 5 out of 8 changed files in this pull request and generated no suggestions.

Files not reviewed (3)

• src/auditwheel/audit.rs: Evaluated as low risk
• src/build_options.rs: Evaluated as low risk
• src/cross_compile.rs: Evaluated as low risk

[messense]

I'm confused why the update to PyO3 0.23 last week didn't break tests using these crates on CI.

Some of these tests are not built but only used to test generating source distribution, will fix them later in a separate PR.