ENH: support shared libraries inside packages

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')

spin/cmds/meson.py

@@ -231,11 +231,6 @@ def _check_coverage_tool_installation(coverage_type: GcovReportFormat, build_dir
         )
 
 
-if sys.platform.startswith("win"):
-    DEFAULT_PREFIX = "C:/"
-else:
-    DEFAULT_PREFIX = "/usr"
-
 build_dir_option = click.option(
     "-C",
     "--build-dir",
@@ -266,10 +261,10 @@ def _check_coverage_tool_installation(coverage_type: GcovReportFormat, build_dir
 )
 @click.option(
     "--prefix",
-    help="The build prefix, passed directly to meson.",
+    help="The build prefix as an absolute path, passed directly to meson.",
     type=str,
     metavar="PREFIX",
-    default=DEFAULT_PREFIX,
+    default="",
 )
 @click.argument("meson_args", nargs=-1)
 @build_dir_option
@@ -316,10 +311,12 @@ def build(
     Which can then be used to build (`spin-clang build`), to test (`spin-clang test ...`), etc.
 
     """
-    abs_build_dir = os.path.abspath(build_dir)
     install_dir = _get_install_dir(build_dir)
     abs_install_dir = os.path.abspath(install_dir)
 
+    if not prefix:
+        prefix = abs_install_dir
+
     cfg = get_config()
     distname = cfg.get("project.name", None)
     if distname and _is_editable_install_of_same_source(distname):
@@ -385,10 +382,6 @@ def build(
             "--only-changed",
             "-C",
             build_dir,
-            "--destdir",
-            install_dir
-            if os.path.isabs(install_dir)
-            else os.path.relpath(abs_install_dir, abs_build_dir),
         ]
         + list(meson_install_args),
         output=(not quiet) and verbose,

spin/tests/test_build_cmds.py

@@ -38,7 +38,8 @@ def test_debug_builds(example_pkg):
 
 def test_prefix_builds(example_pkg):
     """does spin build --prefix create a build-install directory with the correct structure?"""
-    spin("build", "--prefix=/foobar/")
+    prefix = Path.cwd() / "build-install" / "foobar"
+    spin("build", f"--prefix={prefix}")
     assert (Path("build-install") / Path("foobar")).exists()