TST: add package linking a library from a subproject

Note that for Meson versions older than 1.2.0, CI failed with:
```
mesonpy.BuildError: Could not map installation path to an equivalent wheel directory: '{libdir_static}/libexamplelib.a'
```
because the `--skip-subprojects` install option isn't honored.
Hence the test skip on older versions.

In addition, the `c_shared_libs` usage requires Meson 1.3.0

tests/packages/link-library-in-subproject/foo/__init__.py

@@ -0,0 +1,8 @@
+# SPDX-FileCopyrightText: 2024 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+from ._example import example_sum
+
+
+__all__ = ['example_sum']

tests/packages/link-library-in-subproject/foo/_examplemod.c

@@ -0,0 +1,37 @@
+// SPDX-FileCopyrightText: 2022 The meson-python developers
+//
+// SPDX-License-Identifier: MIT
+
+#include <Python.h>
+
+#include "examplelib.h"
+
+static PyObject* example_sum(PyObject* self, PyObject *args)
+{
+    int a, b;
+    if (!PyArg_ParseTuple(args, "ii", &a, &b)) {
+        return NULL;
+    }
+
+    long result = sum(a, b);
+
+    return PyLong_FromLong(result);
+}
+
+static PyMethodDef methods[] = {
+    {"example_sum", (PyCFunction)example_sum, METH_VARARGS, NULL},
+    {NULL, NULL, 0, NULL},
+};
+
+static struct PyModuleDef module = {
+    PyModuleDef_HEAD_INIT,
+    "_example",
+    NULL,
+    -1,
+    methods,
+};
+
+PyMODINIT_FUNC PyInit__example(void)
+{
+    return PyModule_Create(&module);
+}

tests/packages/link-library-in-subproject/foo/meson.build

@@ -0,0 +1,16 @@
+# SPDX-FileCopyrightText: 2022 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+py.extension_module(
+    '_example',
+    '_examplemod.c',
+    dependencies: bar_dep,
+    install: true,
+    subdir: 'foo',
+)
+
+py.install_sources(
+    ['__init__.py'],
+    subdir: 'foo',
+)

tests/packages/link-library-in-subproject/meson.build

@@ -0,0 +1,17 @@
+# SPDX-FileCopyrightText: 2022 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+project(
+    'link-library-in-subproject',
+    'c',
+    version: '1.0.0',
+    meson_version: '>=1.2.0',
+)
+
+py = import('python').find_installation(pure: false)
+
+bar_proj = subproject('bar')
+bar_dep = bar_proj.get_variable('bar_dep')
+
+subdir('foo')

tests/packages/link-library-in-subproject/pyproject.toml

@@ -0,0 +1,15 @@
+# SPDX-FileCopyrightText: 2022 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+[build-system]
+build-backend = 'mesonpy'
+requires = ['meson-python']
+
+[project]
+name = 'link-library-in-subproject'
+version = '1.2.3'
+
+[tool.meson-python.args]
+setup = ['--default-library=static']
+install = ['--skip-subprojects']

tests/packages/link-library-in-subproject/subprojects/bar/bar_dll.h

@@ -0,0 +1,15 @@
+#pragma once
+
+// When building the `examplelib` DLL, this macro expands to `__declspec(dllexport)`
+// so we can annotate symbols appropriately as being exported. When used in
+// headers consuming a DLL, this macro expands to `__declspec(dllimport)` so
+// that consumers know the symbol is defined inside the DLL. In all other cases,
+// the macro expands to nothing.
+// Note: BAR_DLL_{EX,IM}PORTS are set in meson.build
+#if defined(BAR_DLL_EXPORTS)
+    #define BAR_DLL __declspec(dllexport)
+#elif defined(BAR_DLL_IMPORTS)
+    #define BAR_DLL __declspec(dllimport)
+#else
+    #define BAR_DLL
+#endif

tests/packages/link-library-in-subproject/subprojects/bar/examplelib.c

@@ -0,0 +1,9 @@
+// SPDX-FileCopyrightText: 2022 The meson-python developers
+//
+// SPDX-License-Identifier: MIT
+
+#include "bar_dll.h"
+
+BAR_DLL int sum(int a, int b) {
+	return a + b;
+}

tests/packages/link-library-in-subproject/subprojects/bar/examplelib.h

@@ -0,0 +1,7 @@
+// SPDX-FileCopyrightText: 2022 The meson-python developers
+//
+// SPDX-License-Identifier: MIT
+
+#include "bar_dll.h"
+
+BAR_DLL int sum(int a, int b);

tests/packages/link-library-in-subproject/subprojects/bar/meson.build

@@ -0,0 +1,36 @@
+# SPDX-FileCopyrightText: 2022 The meson-python developers
+#
+# SPDX-License-Identifier: MIT
+
+project('bar', 'c', version: '1.2.3', meson_version: '>= 1.3.0')
+
+if get_option('default_library') == 'shared' and meson.get_compiler('c').get_id() in ['msvc', 'clang-cl', 'intel-cl']
+  export_dll_args = ['-DBAR_DLL_EXPORTS']
+  import_dll_args = ['-DBAR_DLL_IMPORTS']
+else
+  export_dll_args = []
+  import_dll_args = []
+endif
+
+example_lib = library(
+    'examplelib',
+    'examplelib.c',
+    c_shared_args: export_dll_args,
+    install: true,
+)
+
+# A second library that we don't link from `foo`. If we install the subproject,
+# this second library also ends up in the wheel. To prevent that, we need to
+# skip installing this `bar` subproject, and statically link `example_lib`.
+unwanted_lib = library(
+    'unwantedlib',
+    'examplelib.c',
+    c_shared_args: export_dll_args,
+    install: true,
+)
+
+bar_dep = declare_dependency(
+  compile_args: import_dll_args,
+  link_with: example_lib,
+  include_directories: '.',
+)

tests/test_wheel.py

@@ -169,6 +169,13 @@ def test_sharedlib_in_package(venv, wheel_sharedlib_in_package):
     assert int(output) == 42
 
 
+@pytest.mark.skipif(MESON_VERSION < (1, 3, 0), reason='Meson version too old')
+def test_link_library_in_subproject(venv, wheel_link_library_in_subproject):
+    venv.pip('install', wheel_link_library_in_subproject)
+    output = venv.python('-c', 'import foo; print(foo.example_sum(3, 6))')
+    assert int(output) == 9
+
+
 @pytest.mark.skipif(sys.platform not in {'linux', 'darwin', 'sunos5'}, reason='Not supported on this platform')
 def test_rpath(wheel_link_against_local_lib, tmp_path):
     artifact = wheel.wheelfile.WheelFile(wheel_link_against_local_lib)