error: using declaration referring to 'sprintf' with internal linkage cannot be exported

[ClausKlein]

clang++ on Linux with libstdc++ and import std;

build-and-test / clang 21 c++23 libstdc++ Release.Default

FAILED: [code=1] CMakeFiles/__cmake_cxx26.dir/Release/usr/share/libc++/v1/std.cppm.o CMakeFiles/__cmake_cxx26.dir/Release/std.pcm 
/usr/local/bin/clang++ -DCMAKE_INTDIR=\"Release\" -I/usr/lib/gcc/x86_64-pc-linux-gnu/15/../../../../lib64/../share/libc++/v1 -stdlib=libc++ -O3  -O3 -DNDEBUG -std=gnu++26 -Wno-reserved-module-identifier -MD -MT CMakeFiles/__cmake_cxx26.dir/Release/usr/share/libc++/v1/std.cppm.o -MF CMakeFiles/__cmake_cxx26.dir/Release/usr/share/libc++/v1/std.cppm.o.d @CMakeFiles/__cmake_cxx26.dir/Release/usr/share/libc++/v1/std.cppm.o.modmap -o CMakeFiles/__cmake_cxx26.dir/Release/usr/share/libc++/v1/std.cppm.o -c /usr/share/libc++/v1/std.cppm
In file included from /usr/share/libc++/v1/std.cppm:199:
/usr/share/libc++/v1/std/cstdio.inc:24:14: error: using declaration referring to 'fprintf' with internal linkage cannot be exported
   24 |   using std::fprintf _LIBCPP_USING_IF_EXISTS;
      |              ^
/usr/include/bits/stdio2.h:123:1: note: target of using declaration
  123 | fprintf (__fortify_clang_overload_arg (FILE *, __restrict, __stream),
      | ^
In file included from /usr/share/libc++/v1/std.cppm:199:
/usr/share/libc++/v1/std/cstdio.inc:37:14: error: using declaration referring to 'printf' with internal linkage cannot be exported
   37 |   using std::printf _LIBCPP_USING_IF_EXISTS;
      |              ^
/usr/include/bits/stdio2.h:135:1: note: target of using declaration
  135 | printf (__fortify_clang_overload_arg (const char *, __restrict, __fmt), ...)
      | ^
In file included from /usr/share/libc++/v1/std.cppm:199:
/usr/share/libc++/v1/std/cstdio.inc:47:14: error: using declaration referring to 'snprintf' with internal linkage cannot be exported
   47 |   using std::snprintf _LIBCPP_USING_IF_EXISTS;
      |              ^
/usr/include/bits/stdio2.h:75:8: note: target of using declaration
   75 | __NTH (snprintf (__fortify_clang_overload_arg (char *, __restrict, __s),
      |        ^
In file included from /usr/share/libc++/v1/std.cppm:199:
/usr/share/libc++/v1/std/cstdio.inc:48:14: error: using declaration referring to 'sprintf' with internal linkage cannot be exported
   48 |   using std::sprintf _LIBCPP_USING_IF_EXISTS;
      |              ^
/usr/include/bits/stdio2.h:37:8: note: target of using declaration
   37 | __NTH (sprintf (__fortify_clang_overload_arg (char *, __restrict, __s),
      |        ^
In file included from /usr/share/libc++/v1/std.cppm:204:
/usr/share/libc++/v1/std/cwchar.inc:30:14: error: using declaration referring to 'swprintf' with internal linkage cannot be exported
   30 |   using std::swprintf _LIBCPP_USING_IF_EXISTS;
      |              ^
/usr/include/bits/wchar2.h:181:8: note: target of using declaration
  181 | __NTH (swprintf (__fortify_clang_overload_arg (wchar_t *, __restrict, __s),
      |        ^
5 errors generated.

[ClausKlein]

@ednolan this error occurs with CMAKE_GENERATOR: Ninja Multi-Config, but the cmake preset tests on linux with Ninja work fine?

[ednolan]

This seems like a Clang compiler bug or a libstdc++ bug to me. We should see whether it reproduces with the Clang trunk CI job (just substitute the string "trunk" for "21" in the CI matrix) and if so, create a minimal reproduction and report it to LLVM (perhaps they'll blame libstdc++, in which case we can kick it over to the GCC bugzilla).

[ednolan]

In general, though, if we're testing modules and the configuration is mixing compiler and standard library implementations, we're probably going to run into issues like this. I think we should restrict support for modules to gcc/libstdc++ and clang/libc++.

[ednolan]

@nickelpro found out that the root cause is a glibc bug that clang lacks a workaround for: llvm/llvm-project#121709