Bug#1102350: libstdc++-15-dev: libstdc++-modules.json points at wrong location (was: cmake 4.0 couldn't find correct std module source file)

[Timo Röhling]

Control: reassign 1102350 libstdc++-15-dev
Control: retitle 1102350 libstdc++-15-dev: libstdc++-modules.json points at 
wrong location

* Leen Hawk <leenh...@leenhawk.com> [2025-04-08 13:47]:

I have change the `CMakeCXXCompiler.cmake`:
```
target_sources(__CMAKE::CXX23
  INTERFACE
  FILE_SET std TYPE CXX_MODULES
    BASE_DIRS  "/usr/lib/gcc/x86_64-linux-gnu/15/../include/c++/15/bits"
    FILES  "/usr/lib/gcc/x86_64-linux-gnu/15/../include/c++/15/bits/std.cc" 
"/usr/lib/gcc/x86_64-linux-gnu/15/../include/c++/15/bits/std.compat.cc")
endif ()
```
to
```
target_sources(__CMAKE::CXX23
  INTERFACE
  FILE_SET std TYPE CXX_MODULES
    BASE_DIRS  "/usr/include/c++/15/bits"
    FILES  "/usr/include/c++/15/bits/std.cc" 
"/usr/include/c++/15/bits/std.compat.cc")
endif ()
```

to fix it. And there is my issue on kitware cmake: https://gitlab.kitware.com/cmake/cmake/-/issues/26609

The source-path in libstdc++-modules.json is broken, and this needs to be fixed in gcc-15, not in cmake.

They have fixed in gentoo and fedora. But debian doesn't.

Nobody filed a bug yet, what do you expect? Especially with an unreleased snapshot of gcc that sits in experimental for a good reason.

Cheers
Timo

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