[BUG]: pybind11-config wrong include flags

[susnux]

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Problem description

After installing the project using cmake the pybind11-config program prints wrong include flags.

% pybind11-config --includes
-I/usr/include/python3.8 -I/usr/lib/python3.8/site-packages/include

The first part (python include directory) is ok, but the pybind11 include path is wrong, there is no /usr/lib/python3.8/site-packages/include.

The problem is this part: https://github.com/pybind/pybind11/blob/e2dcd95407d5202019cecd2bb2827ee6a4a8f9f3/pybind11/commands.py#L13

This only works for not-installed versions, as soon as you install the project using cmake the path is wrong. Probably cmake should insert its installation path into that file after installation (using configure_file).

For me I fixed it using this patch:

diff -Nur pybind11-2.9.2/CMakeLists.txt new/CMakeLists.txt
--- pybind11-2.9.2/CMakeLists.txt	2022-03-31 05:12:13.000000000 +0200
+++ new/CMakeLists.txt	2022-06-08 11:59:32.704707307 +0200
@@ -206,6 +206,8 @@
   file(RELATIVE_PATH CMAKE_INSTALL_INCLUDEDIR ${CMAKE_INSTALL_PREFIX} ${PYTHON_INCLUDE_DIRS})
 endif()
 
+configure_file(pybind11/_config.py.in ${CMAKE_CURRENT_SOURCE_DIR}/pybind11/_config.py @ONLY)
+
 if(PYBIND11_INSTALL)
   install(DIRECTORY ${pybind11_INCLUDE_DIR}/pybind11 DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
   set(PYBIND11_CMAKECONFIG_INSTALL_DIR
diff -Nur pybind11-2.9.2/pybind11/commands.py new/pybind11/commands.py
--- pybind11-2.9.2/pybind11/commands.py	2022-03-31 05:12:13.000000000 +0200
+++ new/pybind11/commands.py	2022-06-08 12:01:48.677372043 +0200
@@ -1,5 +1,6 @@
 # -*- coding: utf-8 -*-
 import os
+from ._config import HEADER_DIR
 
 DIR = os.path.abspath(os.path.dirname(__file__))
 
@@ -8,7 +9,7 @@
     # type: (bool) -> str
     installed_path = os.path.join(DIR, "include")
     source_path = os.path.join(os.path.dirname(DIR), "include")
-    return installed_path if os.path.exists(installed_path) else source_path
+    return HEADER_DIR if os.path.exists(HEADER_DIR) else ( installed_path if os.path.exists(installed_path) else source_path )
 
 
 def get_cmake_dir():
diff -Nur pybind11-2.9.2/pybind11/_config.py.in new/pybind11/_config.py.in
--- pybind11-2.9.2/pybind11/_config.py.in	1970-01-01 01:00:00.000000000 +0100
+++ new/pybind11/_config.py.in	2022-06-08 11:46:25.876860701 +0200
@@ -0,0 +1 @@
+HEADER_DIR = "@CMAKE_INSTALL_FULL_INCLUDEDIR@/pybind11"
diff -Nur pybind11-2.9.2/tests/extra_python_package/test_files.py new/tests/extra_python_package/test_files.py
--- pybind11-2.9.2/tests/extra_python_package/test_files.py	2022-03-31 05:12:13.000000000 +0200
+++ new/tests/extra_python_package/test_files.py	2022-06-08 12:22:22.899405848 +0200
@@ -63,6 +63,7 @@
 py_files = {
     "__init__.py",
     "__main__.py",
+    "_config.py",
     "_version.py",
     "_version.pyi",
     "commands.py",

Reproducible example code

Simply install it using cmake and then use pybind11-config --include

[Skylion007]

Ping @henryiii

[henryiii]

We don't want to break the normal way to install this (via pip), so not fond of adding a new file. Also this would probably not be relocatable? The wheel must be relocatable. I doubt I thought someone would install via CMake only and then try to run via Python, so maybe there are some easy improvements.

[henryiii]

Okay, now I'm confused. pybind11-config is not part of the CMake install at all. It's a Python entry point so it can only be installed via Python. It's not generated by CMake. The CMake install doesn't install any Python parts either. Are you mixing and matching? I'm guessing there's a Python install and that's getting mixed with a manual CMake install? Maybe an old version mixing with a new version, etc?