TST: add a shared library to the example_pkg package

This tests using a shared library from a Python extension module,
which is relevant for SciPy (scipy.special contains such a shared
library).

Author: rgommers

example_pkg/example_pkg/__init__.py

@@ -1,4 +1,20 @@
-from ._core import echo
+import os
+import sys
 
-__all__ = ["echo"]
+__all__ = ["echo", "example_sum"]
 __version__ = "0.0.0dev0"
+
+
+def _enable_sharedlib_loading():
+    basedir = os.path.dirname(__file__)
+    subdir = os.path.join(basedir, "submodule")
+    if os.name == "nt":
+        os.add_dll_directory(subdir)
+    elif sys.platform == "cygwin":
+        os.environ["PATH"] = f'os.environ["PATH"]{os.pathsep}{subdir}'
+
+
+_enable_sharedlib_loading()
+
+
+from ._core import echo, example_sum  # noqa: E402

example_pkg/example_pkg/_core.pyi

@@ -1 +1,2 @@
 def echo(str) -> None: ...
+def example_sum(a: int, b: int) -> int: ...

example_pkg/example_pkg/coremodule.c

@@ -1,6 +1,8 @@
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 
+#include "shlib.h"
+
 static PyObject *
 core_echo(PyObject *self, PyObject *args)
 {
@@ -17,8 +19,21 @@ core_echo(PyObject *self, PyObject *args)
     return ret;
 }
 
+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 CoreMethods[] = {
     {"echo",  core_echo, METH_VARARGS, "Echo a string and return 42"},
+    {"example_sum", example_sum, METH_VARARGS, "Sum up two integers"},
     {NULL, NULL, 0, NULL}        /* Sentinel */
 };
 

example_pkg/example_pkg/meson.build

@@ -1,8 +1,13 @@
+subdir('submodule')
+
 py.extension_module(
   '_core',
   'coremodule.c',
+  include_directories: 'submodule',
+  dependencies: shlib_dep,
   install: true,
-  subdir: 'example_pkg'
+  subdir: 'example_pkg',
+  install_rpath: '$ORIGIN/submodule',
 )
 
 python_sources = [
@@ -15,5 +20,4 @@ py.install_sources(
   subdir: 'example_pkg'
 )
 
-install_subdir('submodule', install_dir: py.get_install_dir() / 'example_pkg')
 install_subdir('tests', install_dir: py.get_install_dir() / 'example_pkg')

example_pkg/example_pkg/submodule/meson.build

@@ -1 +1,29 @@
+# Add a basic shared library, used from the Python extension module
+# in ../coremodule.c
+if meson.get_compiler('c').get_id() in ['msvc', 'clang-cl', 'intel-cl']
+  export_dll_args = ['-DSHLIB_DLL_EXPORTS']
+  import_dll_args = ['-DSHLIB_DLL_IMPORTS']
+else
+  export_dll_args = []
+  import_dll_args = []
+endif
+
+shlib = shared_library(
+  'shlib',
+  'shlib.c',
+  c_args: export_dll_args,
+  install: true,
+  install_dir: py.get_install_dir() / 'example_pkg/submodule',
+)
+
+shlib_dep = declare_dependency(
+  compile_args: import_dll_args,
+  link_with: shlib,
+)
+
+py.install_sources(
+  ['__init__.py'],
+  subdir: 'example_pkg/submodule',
+)
+
 install_subdir('tests', install_dir: py.get_install_dir() / 'example_pkg/submodule')

example_pkg/example_pkg/submodule/shlib.c

@@ -0,0 +1,5 @@
+#include "shlib_dll.h"
+
+SHLIB_DLL int sum(int a, int b) {
+    return a + b;
+}

example_pkg/example_pkg/submodule/shlib.h

@@ -0,0 +1,3 @@
+#include "shlib_dll.h"
+
+SHLIB_DLL int sum(int a, int b);

example_pkg/example_pkg/submodule/shlib_dll.h

@@ -0,0 +1,14 @@
+#pragma once
+
+// Windows support. When building the `shlib` 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.
+#if defined(SHLIB_DLL_EXPORTS)
+    #define SHLIB_DLL __declspec(dllexport)
+#elif defined(SHLIB_DLL_IMPORTS)
+    #define SHLIB_DLL __declspec(dllimport)
+#else
+    #define SHLIB_DLL
+#endif

example_pkg/meson.build

@@ -13,8 +13,7 @@ project(
 
 cc = meson.get_compiler('c')
 
-py_mod = import('python')
-py = py_mod.find_installation(pure: false)
+py = import('python').find_installation(pure: false)
 py_dep = py.dependency()
 
 subdir('example_pkg')