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1. lunixbochs

   added

   type-bugAn unexpected behavior, bug, or errorAn unexpected behavior, bug, or error

   on Oct 13, 2023
2. AlexWaygood

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   OS-mac

   on Oct 13, 2023
3. vstinner commented on Oct 31, 2023

   

   vstinner

   on Oct 31, 2023

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   What is your clang version?
4. vstinner

   added

   topic-C-API

   on Oct 31, 2023
5. ronaldoussoren commented on Nov 5, 2023

   

   ronaldoussoren

   on Nov 5, 2023

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   Also, please add a minimal example on how to reproduce the issue.

   FWIW, I tried to reproduce using the following trivial code as a c++ file (.cc suffix):

   #include <cctype>
   #include "Python.h"

   This worked fine when building with "cc -c repro.cc" using the clang included with the current Xcode 15.1 beta.

   Version Details

   Xcode:

   Xcode 15.1
   Build version 15C5042i
   

   Clang:

   Apple clang version 15.0.0 (clang-1500.1.0.2.4)
   Target: arm64-apple-darwin23.1.0
   Thread model: posix
   InstalledDir: /Users/ronald/Applications/Xcode-beta.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
   
6. lunixbochs commented on Nov 10, 2023

   

   lunixbochs

   on Nov 10, 2023

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   This triggers it for me:

   cc `python3.11-config --includes` -fmodules -fcxx-modules test.cpp
7. vstinner commented on Nov 10, 2023

   

   vstinner

   on Nov 10, 2023

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   Can you provide the minimum test.cpp file reproducing the issue?
8. ronaldoussoren commented on Nov 10, 2023

   

   ronaldoussoren

   on Nov 10, 2023

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   Can you provide the minimum test.cpp file reproducing the issue?

   The two-line file in my previous comment is enough to reproduce the issue (with 3.9 or later)

   The error goes away if I add -Wno-module-import-in-extern-c to the compiler arguments, but that's almost certainly not the right fix (and I haven't tried building an extension with modules enabled and this flag to suppress the error).

   Actually avoiding the error requires non-trivial reorganisation of our header files to ensure that all includes of system headers are done outside of extern "C" blocks.
9. lunixbochs commented on Nov 10, 2023

   

   lunixbochs

   on Nov 10, 2023

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   Actually avoiding the error requires non-trivial reorganisation of our header files to ensure that all includes of system headers are done outside of extern "C" blocks.

   It looks like these changes for 3.13 already have the correct reorganization, they'd just need to be backported: #108769
10. ronaldoussoren commented on Dec 8, 2023

    

    ronaldoussoren

    on Dec 8, 2023

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    @vstinner : Are the changes in #108769 something that can be back ported to 3.11 and 3.12? I'm worried that moving includes around can affect 3th-party extensions.

    Alternatively we can document that Python 3.12 and earlier don't support building with C++ modules enabled, and add a test based on my earlier message to 3.13 to ensure that building with modules continues working there.
11. vstinner commented on Feb 7, 2024

    

    vstinner

    on Feb 7, 2024

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    I reproduced a similar error using a manually created C++20 module.

    Work in the Lib/test/test_cppext/ directory.

    Create Lib/test/test_cppext/mymodule.cppm:

    export module mymodule;
    

    Create Lib/test/test_cppext/Makefile:

    CXX=clang++
    CXXFLAGS=-std=c++20 -fmodules -fprebuilt-module-path=. -fno-strict-overflow -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -g -O0 -fPIC
    
    mymodule.pcm: mymodule.cppm
    	$(CXX) $(CXXFLAGS) --precompile mymodule.cppm -o $@
    	$(CXX) $(CXXFLAGS) -c mymodule.pcm -o mymodule.o
    
    clean:
    	rm -rf mymodule.pcm mymodule.o
    

    Pre-compile mymodule.cppm using the Makefile in Lib/test/test_cppext/:

    make
    

    Modify Lib/test/test_cppext/extension.cpp, before #include "Python.h", add:

    extern "C" {
        import mymodule;
    }

    Build the C++ extension with:

    ../../../python -m venv env
    env/bin/python -m pip install setuptools
    rm -rf build
    CC=clang++ CXX=clang++ CFLAGS="-fmodules -fprebuilt-module-path=." CPYTHON_TEST_CPP_STD=c++20 CPYTHON_TEST_EXT_NAME=extname env/bin/python setup.py build_ext
    

    Building the C++ extension fails with:

    extension.cpp:10:1: error: unknown type name 'import'
        2 | import mymodule;        // import declaration
          | ^
    1 error generated.
    

    What I understood:

    • On macOS, some system header files use import ... if built with C++.
    • <Python.h> includes some system header files inside extern "C" { ... }. In this case, building <Python.h> with C++20 modules fails with an error.

    In short:

    • #include ... must not be done inside extern "C" { ... }.
    • #include ... can be indirect, header A can include header B which includes a system header.
    • Moving most system headers to Python.h makes it easier since Python.h doesn't use extern "C" { ... }.
12. vstinner commented on Feb 7, 2024

    

    vstinner

    on Feb 7, 2024

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    Moving most system headers to Python.h makes it easier since Python.h doesn't use extern "C" { ... }.

    The problem also exists for the internal C API: see #115105.
13. vstinner commented on Jan 27, 2025

    

    vstinner

    on Jan 27, 2025

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    Since only Python 3.12 is impacted (Python 3.11 no longer gets bugfixes) and the lack of activity for one year, I suggest closing this old issue as "WONT FIX".
14. vstinner

    closed this as not plannedon Feb 27, 2025
15. vstinner commented on Feb 27, 2025

    

    vstinner

    on Feb 27, 2025

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    This issue has been fixed in Python 3.13.