TST: add Rust extension module using PyO3

This requires nightly Rust and unreleased Meson, and it currently
bumps into a Meson warning: ``WARNING: Library entry portable_atomic
has unexpected keys "doc-scrape-examples"``.

Author: dnicolodi

tests/conftest.py

@@ -224,6 +224,10 @@ def __init__(self, source_dir, build_dir, meson_args=None, editable_verbose=None
                 # keeps working.
                 'link-against-local-lib',
 
+                # The ``rust-pyo3`` package bumps into this Meson
+                # warning: ``WARNING: Library entry portable_atomic
+                # has unexpected keys "doc-scrape-examples"``.
+                'rust-pyo3',
         }:
             if meson_args is None:
                 meson_args = {}

tests/packages/rust-pyo3/Cargo.lock

@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: 2026 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+[package]
+name = "rust-pyo3"
+version = "1.0.0"
+edition = "2024"
+
+[lib]
+name = "rust_pyo3"
+crate-type = ["cdylib"]
+
+[dependencies]
+pyo3 = "0.29.0"

tests/packages/rust-pyo3/Cargo.toml

@@ -0,0 +1,17 @@
+# SPDX-FileCopyrightText: 2026 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+project('rust-pyo3', 'c', 'rust', version: '1.0.0', meson_version: '>= 1.12.0', default_options: ['rust_std=2024'])
+
+py = import('python').find_installation(pure: false)
+pkg = import('rust').workspace().package()
+
+py.extension_module(
+    'rust_pyo3',
+    'src/lib.rs',
+    rust_dependency_map : pkg.rust_dependency_map(),
+    rust_args: pkg.rust_args(),
+    dependencies : pkg.dependencies(),
+    install: true,
+)

tests/packages/rust-pyo3/meson.build

@@ -0,0 +1,10 @@
+# SPDX-FileCopyrightText: 2021 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+[build-system]
+build-backend = "mesonpy"
+requires = ["meson-python"]
+
+[tool.meson-python.args]
+setup = ['--vsenv']

tests/packages/rust-pyo3/pyproject.toml

@@ -0,0 +1,16 @@
+// SPDX-FileCopyrightText: 2026 The meson-python developers
+//
+// SPDX-License-Identifier: MIT
+
+use pyo3::prelude::*;
+
+#[pymodule]
+mod rust_pyo3 {
+    use pyo3::prelude::*;
+
+    /// Sum two numbers.
+    #[pyfunction]
+    fn sum(a: i64, b: i64) -> PyResult<i64> {
+        Ok(a + b)
+    }
+}

tests/packages/rust-pyo3/src/lib.rs

@@ -0,0 +1 @@
+extra_args += cargo_ws.subproject('pyo3-ffi', pkg_obj.api(), native: false).dependency().get_variable('args').split('\0')