feat(cmake): add installation support for pkg-config dependency detection (#4077)

* add installation support for pkg-config dependency detection

pkg-config is a buildsystem-agnostic alternative to
`pybind11Config.cmake` that can be used from build systems other than
cmake.

Fixes #230

* tests: add test for pkg config

Signed-off-by: Henry Schreiner <henryschreineriii@gmail.com>

Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>

.pre-commit-config.yaml

@@ -12,6 +12,9 @@
 #
 # See https://github.com/pre-commit/pre-commit
 
+# third-party content
+exclude: ^tools/JoinPaths.cmake$
+
 repos:
 # Standard hooks
 - repo: https://github.com/pre-commit/pre-commit-hooks

CMakeLists.txt

@@ -198,6 +198,9 @@ else()
 endif()
 
 include("${CMAKE_CURRENT_SOURCE_DIR}/tools/pybind11Common.cmake")
+# https://github.com/jtojnar/cmake-snips/#concatenating-paths-when-building-pkg-config-files
+# TODO: cmake 3.20 adds the cmake_path() function, which obsoletes this snippet
+include("${CMAKE_CURRENT_SOURCE_DIR}/tools/JoinPaths.cmake")
 
 # Relative directory setting
 if(USE_PYTHON_INCLUDE_DIR AND DEFINED Python_INCLUDE_DIRS)
@@ -262,6 +265,16 @@ if(PYBIND11_INSTALL)
     NAMESPACE "pybind11::"
     DESTINATION ${PYBIND11_CMAKECONFIG_INSTALL_DIR})
 
+  # pkg-config support
+  if(NOT prefix_for_pc_file)
+    set(prefix_for_pc_file "${CMAKE_INSTALL_PREFIX}")
+  endif()
+  join_paths(includedir_for_pc_file "\${prefix}" "${CMAKE_INSTALL_INCLUDEDIR}")
+  configure_file("${CMAKE_CURRENT_SOURCE_DIR}/tools/pybind11.pc.in"
+                 "${CMAKE_CURRENT_BINARY_DIR}/pybind11.pc" @ONLY)
+  install(FILES "${CMAKE_CURRENT_BINARY_DIR}/pybind11.pc"
+          DESTINATION "${CMAKE_INSTALL_DATAROOTDIR}/pkgconfig/")
+
   # Uninstall target
   if(PYBIND11_MASTER_PROJECT)
     configure_file("${CMAKE_CURRENT_SOURCE_DIR}/tools/cmake_uninstall.cmake.in"

noxfile.py

@@ -27,7 +27,7 @@ def lint(session: nox.Session) -> None:
     Lint the codebase (except for clang-format/tidy).
     """
     session.install("pre-commit")
-    session.run("pre-commit", "run", "-a")
+    session.run("pre-commit", "run", "-a", *session.posargs)
 
 
 @nox.session(python=PYTHON_VERSIONS)
@@ -58,7 +58,7 @@ def tests_packaging(session: nox.Session) -> None:
     """
 
     session.install("-r", "tests/requirements.txt", "--prefer-binary")
-    session.run("pytest", "tests/extra_python_package")
+    session.run("pytest", "tests/extra_python_package", *session.posargs)
 
 
 @nox.session(reuse_venv=True)

pybind11/__init__.py

@@ -6,11 +6,12 @@ if sys.version_info < (3, 6):
 
 
 from ._version import __version__, version_info
-from .commands import get_cmake_dir, get_include
+from .commands import get_cmake_dir, get_include, get_pkgconfig_dir
 
 __all__ = (
     "version_info",
     "__version__",
     "get_include",
     "get_cmake_dir",
+    "get_pkgconfig_dir",
 )

pybind11/__main__.py

@@ -4,7 +4,7 @@ import argparse
 import sys
 import sysconfig
 
-from .commands import get_cmake_dir, get_include
+from .commands import get_cmake_dir, get_include, get_pkgconfig_dir
 
 
 def print_includes() -> None:
@@ -36,6 +36,11 @@ def main() -> None:
         action="store_true",
         help="Print the CMake module directory, ideal for setting -Dpybind11_ROOT in CMake.",
     )
+    parser.add_argument(
+        "--pkgconfigdir",
+        action="store_true",
+        help="Print the pkgconfig directory, ideal for setting $PKG_CONFIG_PATH.",
+    )
     args = parser.parse_args()
     if not sys.argv[1:]:
         parser.print_help()
@@ -43,6 +48,8 @@ def main() -> None:
         print_includes()
     if args.cmakedir:
         print(get_cmake_dir())
+    if args.pkgconfigdir:
+        print(get_pkgconfig_dir())
 
 
 if __name__ == "__main__":

pybind11/commands.py

@@ -23,3 +23,15 @@ def get_cmake_dir() -> str:
 
     msg = "pybind11 not installed, installation required to access the CMake files"
     raise ImportError(msg)
+
+
+def get_pkgconfig_dir() -> str:
+    """
+    Return the path to the pybind11 pkgconfig directory.
+    """
+    pkgconfig_installed_path = os.path.join(DIR, "share", "pkgconfig")
+    if os.path.exists(pkgconfig_installed_path):
+        return pkgconfig_installed_path
+
+    msg = "pybind11 not installed, installation required to access the pkgconfig files"
+    raise ImportError(msg)

setup.py

@@ -127,6 +127,7 @@ with remove_output("pybind11/include", "pybind11/share"):
             "-DCMAKE_INSTALL_PREFIX=pybind11",
             "-DBUILD_TESTING=OFF",
             "-DPYBIND11_NOPYTHON=ON",
+            "-Dprefix_for_pc_file=${pcfiledir}/../../",
         ]
         if "CMAKE_ARGS" in os.environ:
             fcommand = [

tests/extra_python_package/test_files.py

@@ -12,6 +12,16 @@ import zipfile
 DIR = os.path.abspath(os.path.dirname(__file__))
 MAIN_DIR = os.path.dirname(os.path.dirname(DIR))
 
+PKGCONFIG = """\
+prefix=${{pcfiledir}}/../../
+includedir=${{prefix}}/include
+
+Name: pybind11
+Description: Seamless operability between C++11 and Python
+Version: {VERSION}
+Cflags: -I${{includedir}}
+"""
+
 
 main_headers = {
     "include/pybind11/attr.h",
@@ -59,6 +69,10 @@ cmake_files = {
     "share/cmake/pybind11/pybind11Tools.cmake",
 }
 
+pkgconfig_files = {
+    "share/pkgconfig/pybind11.pc",
+}
+
 py_files = {
     "__init__.py",
     "__main__.py",
@@ -69,7 +83,7 @@ py_files = {
 }
 
 headers = main_headers | detail_headers | stl_headers
-src_files = headers | cmake_files
+src_files = headers | cmake_files | pkgconfig_files
 all_files = src_files | py_files
 
 
@@ -82,6 +96,7 @@ sdist_files = {
     "pybind11/share",
     "pybind11/share/cmake",
     "pybind11/share/cmake/pybind11",
+    "pybind11/share/pkgconfig",
     "pyproject.toml",
     "setup.cfg",
     "setup.py",
@@ -101,22 +116,25 @@ local_sdist_files = {
 }
 
 
+def read_tz_file(tar: tarfile.TarFile, name: str) -> bytes:
+    start = tar.getnames()[0] + "/"
+    inner_file = tar.extractfile(tar.getmember(f"{start}{name}"))
+    assert inner_file
+    with contextlib.closing(inner_file) as f:
+        return f.read()
+
+
+def normalize_line_endings(value: bytes) -> bytes:
+    return value.replace(os.linesep.encode("utf-8"), b"\n")
+
+
 def test_build_sdist(monkeypatch, tmpdir):
 
     monkeypatch.chdir(MAIN_DIR)
 
-    out = subprocess.check_output(
-        [
-            sys.executable,
-            "-m",
-            "build",
-            "--sdist",
-            "--outdir",
-            str(tmpdir),
-        ]
+    subprocess.run(
+        [sys.executable, "-m", "build", "--sdist", f"--outdir={tmpdir}"], check=True
     )
-    if hasattr(out, "decode"):
-        out = out.decode()
 
     (sdist,) = tmpdir.visit("*.tar.gz")
 
@@ -125,25 +143,17 @@ def test_build_sdist(monkeypatch, tmpdir):
         version = start[9:-1]
         simpler = {n.split("/", 1)[-1] for n in tar.getnames()[1:]}
 
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "setup.py"))
-        ) as f:
-            setup_py = f.read()
-
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "pyproject.toml"))
-        ) as f:
-            pyproject_toml = f.read()
-
-        with contextlib.closing(
-            tar.extractfile(
-                tar.getmember(
-                    start + "pybind11/share/cmake/pybind11/pybind11Config.cmake"
-                )
-            )
-        ) as f:
-            contents = f.read().decode("utf8")
-        assert 'set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include")' in contents
+        setup_py = read_tz_file(tar, "setup.py")
+        pyproject_toml = read_tz_file(tar, "pyproject.toml")
+        pkgconfig = read_tz_file(tar, "pybind11/share/pkgconfig/pybind11.pc")
+        cmake_cfg = read_tz_file(
+            tar, "pybind11/share/cmake/pybind11/pybind11Config.cmake"
+        )
+
+    assert (
+        'set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include")'
+        in cmake_cfg.decode("utf-8")
+    )
 
     files = {f"pybind11/{n}" for n in all_files}
     files |= sdist_files
@@ -154,9 +164,9 @@ def test_build_sdist(monkeypatch, tmpdir):
 
     with open(os.path.join(MAIN_DIR, "tools", "setup_main.py.in"), "rb") as f:
         contents = (
-            string.Template(f.read().decode())
+            string.Template(f.read().decode("utf-8"))
             .substitute(version=version, extra_cmd="")
-            .encode()
+            .encode("utf-8")
         )
     assert setup_py == contents
 
@@ -164,25 +174,19 @@ def test_build_sdist(monkeypatch, tmpdir):
         contents = f.read()
     assert pyproject_toml == contents
 
+    simple_version = ".".join(version.split(".")[:3])
+    pkgconfig_expected = PKGCONFIG.format(VERSION=simple_version).encode("utf-8")
+    assert normalize_line_endings(pkgconfig) == pkgconfig_expected
+
 
 def test_build_global_dist(monkeypatch, tmpdir):
 
     monkeypatch.chdir(MAIN_DIR)
     monkeypatch.setenv("PYBIND11_GLOBAL_SDIST", "1")
-    out = subprocess.check_output(
-        [
-            sys.executable,
-            "-m",
-            "build",
-            "--sdist",
-            "--outdir",
-            str(tmpdir),
-        ]
+    subprocess.run(
+        [sys.executable, "-m", "build", "--sdist", "--outdir", str(tmpdir)], check=True
     )
 
-    if hasattr(out, "decode"):
-        out = out.decode()
-
     (sdist,) = tmpdir.visit("*.tar.gz")
 
     with tarfile.open(str(sdist), "r:gz") as tar:
@@ -190,15 +194,17 @@ def test_build_global_dist(monkeypatch, tmpdir):
         version = start[16:-1]
         simpler = {n.split("/", 1)[-1] for n in tar.getnames()[1:]}
 
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "setup.py"))
-        ) as f:
-            setup_py = f.read()
+        setup_py = read_tz_file(tar, "setup.py")
+        pyproject_toml = read_tz_file(tar, "pyproject.toml")
+        pkgconfig = read_tz_file(tar, "pybind11/share/pkgconfig/pybind11.pc")
+        cmake_cfg = read_tz_file(
+            tar, "pybind11/share/cmake/pybind11/pybind11Config.cmake"
+        )
 
-        with contextlib.closing(
-            tar.extractfile(tar.getmember(start + "pyproject.toml"))
-        ) as f:
-            pyproject_toml = f.read()
+    assert (
+        'set(pybind11_INCLUDE_DIR "${PACKAGE_PREFIX_DIR}/include")'
+        in cmake_cfg.decode("utf-8")
+    )
 
     files = {f"pybind11/{n}" for n in all_files}
     files |= sdist_files
@@ -209,7 +215,7 @@ def test_build_global_dist(monkeypatch, tmpdir):
         contents = (
             string.Template(f.read().decode())
             .substitute(version=version, extra_cmd="")
-            .encode()
+            .encode("utf-8")
         )
         assert setup_py == contents
 
@@ -217,12 +223,16 @@ def test_build_global_dist(monkeypatch, tmpdir):
         contents = f.read()
         assert pyproject_toml == contents
 
+    simple_version = ".".join(version.split(".")[:3])
+    pkgconfig_expected = PKGCONFIG.format(VERSION=simple_version).encode("utf-8")
+    assert normalize_line_endings(pkgconfig) == pkgconfig_expected
+
 
 def tests_build_wheel(monkeypatch, tmpdir):
     monkeypatch.chdir(MAIN_DIR)
 
-    subprocess.check_output(
-        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)]
+    subprocess.run(
+        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)], check=True
     )
 
     (wheel,) = tmpdir.visit("*.whl")
@@ -249,8 +259,8 @@ def tests_build_global_wheel(monkeypatch, tmpdir):
     monkeypatch.chdir(MAIN_DIR)
     monkeypatch.setenv("PYBIND11_GLOBAL_SDIST", "1")
 
-    subprocess.check_output(
-        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)]
+    subprocess.run(
+        [sys.executable, "-m", "pip", "wheel", ".", "-w", str(tmpdir)], check=True
     )
 
     (wheel,) = tmpdir.visit("*.whl")

tools/JoinPaths.cmake

@@ -0,0 +1,23 @@
+# This module provides function for joining paths
+# known from most languages
+#
+# SPDX-License-Identifier: (MIT OR CC0-1.0)
+# Copyright 2020 Jan Tojnar
+# https://github.com/jtojnar/cmake-snips
+#
+# Modelled after Python’s os.path.join
+# https://docs.python.org/3.7/library/os.path.html#os.path.join
+# Windows not supported
+function(join_paths joined_path first_path_segment)
+    set(temp_path "${first_path_segment}")
+    foreach(current_segment IN LISTS ARGN)
+        if(NOT ("${current_segment}" STREQUAL ""))
+            if(IS_ABSOLUTE "${current_segment}")
+                set(temp_path "${current_segment}")
+            else()
+                set(temp_path "${temp_path}/${current_segment}")
+            endif()
+        endif()
+    endforeach()
+    set(${joined_path} "${temp_path}" PARENT_SCOPE)
+endfunction()

tools/pybind11.pc.in

@@ -0,0 +1,7 @@
+prefix=@prefix_for_pc_file@
+includedir=@includedir_for_pc_file@
+
+Name: @PROJECT_NAME@
+Description: Seamless operability between C++11 and Python
+Version: @PROJECT_VERSION@
+Cflags: -I${includedir}

tools/setup_global.py.in

@@ -29,6 +29,7 @@ main_headers = glob.glob("pybind11/include/pybind11/*.h")
 detail_headers = glob.glob("pybind11/include/pybind11/detail/*.h")
 stl_headers = glob.glob("pybind11/include/pybind11/stl/*.h")
 cmake_files = glob.glob("pybind11/share/cmake/pybind11/*.cmake")
+pkgconfig_files = glob.glob("pybind11/share/pkgconfig/*.pc")
 headers = main_headers + detail_headers + stl_headers
 
 cmdclass = {"install_headers": InstallHeadersNested}
@@ -51,6 +52,7 @@ setup(
     headers=headers,
     data_files=[
         (base + "share/cmake/pybind11", cmake_files),
+        (base + "share/pkgconfig", pkgconfig_files),
         (base + "include/pybind11", main_headers),
         (base + "include/pybind11/detail", detail_headers),
         (base + "include/pybind11/stl", stl_headers),

tools/setup_main.py.in

@@ -17,6 +17,7 @@ setup(
         "pybind11.include.pybind11.detail",
         "pybind11.include.pybind11.stl",
         "pybind11.share.cmake.pybind11",
+        "pybind11.share.pkgconfig",
     ],
     package_data={
         "pybind11": ["py.typed"],
@@ -24,6 +25,7 @@ setup(
         "pybind11.include.pybind11.detail": ["*.h"],
         "pybind11.include.pybind11.stl": ["*.h"],
         "pybind11.share.cmake.pybind11": ["*.cmake"],
+        "pybind11.share.pkgconfig": ["*.pc"],
     },
     extras_require={
         "global": ["pybind11_global==$version"]