[Bug libstdc++/109647] New: ranges:6151:14: error: requires clause differs in template redeclaration rejected by clang++ 16.0.2

[Bug libstdc++/109647] New: ranges:6151:14: error: requires clause differs in template redeclaration rejected by clang++ 16.0.2

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109647

            Bug ID: 109647
           Summary: ranges:6151:14: error: requires clause differs in
                    template redeclaration rejected by clang++ 16.0.2
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: marxin at gcc dot gnu.org
                CC: redi at gcc dot gnu.org
  Target Milestone: ---

Apparently, clang++ 16.0.2 can't digest libstdc++ version of ranges header
file:

echo '#include <ranges>' | clang++ -x c++ - -c -std=c++2b
In file included from <stdin>:1:
/usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/ranges:6151:14:
error: requires clause differs in template redeclaration
    requires forward_range<_Vp>
             ^
/usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/ranges:5850:14:
note: previous template declaration is here
    requires input_range<_Vp>
             ^
/usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/ranges:8846:20:
error: type-id cannot have a name
    { return (auto(__x) += __y); }
                   ^
/usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/ranges:8846:25:
error: expected ')'
    { return (auto(__x) += __y); }
                        ^
/usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/ranges:8846:14:
note: to match this '('
    { return (auto(__x) += __y); }
             ^
/usr/bin/../lib64/gcc/x86_64-suse-linux/13/../../../../include/c++/13/ranges:8846:32:
error: expected expression
    { return (auto(__x) += __y); }
                               ^
4 errors generated.

$ echo '#include <ranges>' | g++-13 -x c++ - -c -std=c++2b
(ok)

[Bug libstdc++/109647] ranges:6151:14: error: requires clause differs in template redeclaration rejected by clang++ 16.0.2

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109647

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |INVALID
             Status|UNCONFIRMED                 |RESOLVED

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
This is a clang bug.

The primary template on line 5850 has these constraints:

  template<view _Vp>
    requires input_range<_Vp>
  class chunk_view : public view_interface<chunk_view<_Vp>>


But then there is a partial specialization for forward_range on line 6075:

  template<view _Vp>
    requires forward_range<_Vp>
  class chunk_view<_Vp> : public view_interface<chunk_view<_Vp>>

The error on line 6151 incorrectly says that the definition is inconstistent
with line 5850. That's true, but it's a definition for the one on line 6075
instead.

[Bug libstdc++/109647] ranges:6151:14: error: requires clause differs in template redeclaration rejected by clang++ 16.0.2

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109647

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
As already explained in Bug 96830 comment 8 

This is https://github.com/llvm/llvm-project/issues/49620 which is fixed on
trunk, but still present in Clang 16.0.0