[C++23] [Modules] `-fskip-odr-check-in-gmf` results in "redefinition of concept" error

[jiixyj]

I'm testing with LLVM/Clang head (607b4bc). I have some code where I #include after doing an import:

import utpp;
#include <fstream>
#include <numeric>
#include <streambuf>
#include <string>

When compiling with -fskip-odr-check-in-gmf (which is the default now, I think), I'm getting a "redefinition of concept" error:

/llvm-project/prefix/bin/clang++   -m64 -stdlib=libc++ -Xclang -fskip-odr-check-in-gmf -Wno-deprecated-declarations -O2 -g -DNDEBUG -std=c++23 -fcolor-diagnostics -MD -MT example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o -MF example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o.d @example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o.modmap -o example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o -c /home/jan/git/utpp/example/gherkin.cpp
In file included from /home/jan/git/utpp/example/gherkin.cpp:9:
In file included from /llvm-project/prefix/bin/../include/c++/v1/fstream:199:                           
In file included from /llvm-project/prefix/bin/../include/c++/v1/filesystem:538:                        
In file included from /llvm-project/prefix/bin/../include/c++/v1/__filesystem/directory_entry.h:20:     
In file included from /llvm-project/prefix/bin/../include/c++/v1/__filesystem/filesystem_error.h:15:    
In file included from /llvm-project/prefix/bin/../include/c++/v1/__filesystem/path.h:30:                
In file included from /llvm-project/prefix/bin/../include/c++/v1/iomanip:46:                            
In file included from /llvm-project/prefix/bin/../include/c++/v1/istream:170:                           
In file included from /llvm-project/prefix/bin/../include/c++/v1/ostream:188:
In file included from /llvm-project/prefix/bin/../include/c++/v1/format:194:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/container_adaptor.h:20:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/range_default_formatter.h:23:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/range_formatter.h:23:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/format_context.h:30:
/llvm-project/prefix/bin/../include/c++/v1/optional:565:9: error: redefinition of concept '__is_derived_from_optional' with different template parameters or requirem
ents
  565 | concept __is_derived_from_optional = requires(const _Tp& __t) { []<class _Up>(const optional<_Up>&) {}(__t); };
      |         ^
/llvm-project/prefix/bin/../include/c++/v1/__ranges/movable_box.h:21:10: note: '/llvm-project/prefix/bin/../include/c++/v1/optional' inclu
ded multiple times, additional include site in header from module 'std.<global>'
   21 | #include <optional>
      |          ^
/llvm-project/prefix/share/libc++/v1/std.cppm:14:1: note: std.<global> defined here
   14 | module;
      | ^
/llvm-project/prefix/bin/../include/c++/v1/__format/format_context.h:30:12: note: '/llvm-project/prefix/bin/../include/c++/v1/optional' in
cluded multiple times, additional include site here
   30 | #  include <optional>
      |            ^

When compiling with -fno-skip-odr-check-in-gmf, it finishes compiling without error. Which is curious, since I had assumed that enabling -fskip-odr-check-in-gmf would always result in less errors, not more.

Another data point: on LLVM/Clang from 2024-02-22, this compiled without error without any additional compiler arguments.

So now, I have to do one of the following to make the error go away:

• Specify -fno-skip-odr-check-in-gmf
• or move the import after the #includes

Has anyone an idea how/why this could happen? I could try to bisect this, but this could take a while...

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: Jan Kokemüller (jiixyj)

I'm testing with LLVM/Clang head (607b4bc). I have some code where I `#include` _after_ doing an `import`:

import utpp;
#include <fstream>
#include <numeric>
#include <streambuf>
#include <string>

When compiling with -fskip-odr-check-in-gmf (which is the default now, I think), I'm getting a "redefinition of concept" error:

/llvm-project/prefix/bin/clang++   -m64 -stdlib=libc++ -Xclang -fskip-odr-check-in-gmf -Wno-deprecated-declarations -O2 -g -DNDEBUG -std=c++23 -fcolor-diagnostics -MD -MT example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o -MF example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o.d @<!-- -->example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o.modmap -o example/CMakeFiles/utpp_gherkin_feature.dir/gherkin.cpp.o -c /home/jan/git/utpp/example/gherkin.cpp
In file included from /home/jan/git/utpp/example/gherkin.cpp:9:
In file included from /llvm-project/prefix/bin/../include/c++/v1/fstream:199:                           
In file included from /llvm-project/prefix/bin/../include/c++/v1/filesystem:538:                        
In file included from /llvm-project/prefix/bin/../include/c++/v1/__filesystem/directory_entry.h:20:     
In file included from /llvm-project/prefix/bin/../include/c++/v1/__filesystem/filesystem_error.h:15:    
In file included from /llvm-project/prefix/bin/../include/c++/v1/__filesystem/path.h:30:                
In file included from /llvm-project/prefix/bin/../include/c++/v1/iomanip:46:                            
In file included from /llvm-project/prefix/bin/../include/c++/v1/istream:170:                           
In file included from /llvm-project/prefix/bin/../include/c++/v1/ostream:188:
In file included from /llvm-project/prefix/bin/../include/c++/v1/format:194:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/container_adaptor.h:20:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/range_default_formatter.h:23:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/range_formatter.h:23:
In file included from /llvm-project/prefix/bin/../include/c++/v1/__format/format_context.h:30:
/llvm-project/prefix/bin/../include/c++/v1/optional:565:9: error: redefinition of concept '__is_derived_from_optional' with different template parameters or requirem
ents
  565 | concept __is_derived_from_optional = requires(const _Tp&amp; __t) { []&lt;class _Up&gt;(const optional&lt;_Up&gt;&amp;) {}(__t); };
      |         ^
/llvm-project/prefix/bin/../include/c++/v1/__ranges/movable_box.h:21:10: note: '/llvm-project/prefix/bin/../include/c++/v1/optional' inclu
ded multiple times, additional include site in header from module 'std.&lt;global&gt;'
   21 | #include &lt;optional&gt;
      |          ^
/llvm-project/prefix/share/libc++/v1/std.cppm:14:1: note: std.&lt;global&gt; defined here
   14 | module;
      | ^
/llvm-project/prefix/bin/../include/c++/v1/__format/format_context.h:30:12: note: '/llvm-project/prefix/bin/../include/c++/v1/optional' in
cluded multiple times, additional include site here
   30 | #  include &lt;optional&gt;
      |            ^

When compiling with -fno-skip-odr-check-in-gmf, it finishes compiling without error. Which is curious, since I had assumed that enabling -fskip-odr-check-in-gmf would always result in less errors, not more.

Another data point: on LLVM/Clang from 2024-02-22, this compiled without error without any additional compiler arguments.

So now, I have to do one of the following to make the error go away:

• Specify -fno-skip-odr-check-in-gmf
• or move the import after the #includes

Has anyone an idea how/why this could happen? I could try to bisect this, but this could take a while...

[ChuanqiXu9]

I guess the reason may be that we used ODRHash to merge concepts in (import-before-include) path. A reduced (without any stl) may be helpful.

[ChuanqiXu9]

Although I marked this as closed in the commit, I didn't try the original reproducer. So feel free to reopen this if there is still problems.

[jiixyj]

Thank you! I can confirm that the fix works. I tested with 8cee94e .