Re: [r16-7292 Regression] FAIL: g++.dg/concepts/expression.C -std=gnu++17 (test for excess errors) on Linux/x86_64

On 2/6/26 2:29 AM, Haochen Jiang wrote:
> On Linux/x86_64,
> 
> 3f7905550483408a2c4c5096a1adc8d7e863eb12 is the first bad commit
> commit 3f7905550483408a2c4c5096a1adc8d7e863eb12
> Author: Nathan Myers <[email protected]>
> Date:   Mon Sep 22 23:52:52 2025 -0400
> 
>      libstdc++: container erasure overloads (P2077) [PR117404]
> 
> caused
> 
> FAIL: g++.dg/concepts/expression.C  -std=gnu++17 (test for excess errors)
> 
> with GCC configured with
> 
> ../../gcc/configure --prefix=/export/users3/haochenj/src/gcc-bisect/master/master/r16-7292/usr --enable-clocale=gnu --with-system-zlib --with-demangler-in-ld --with-fpmath=sse --enable-languages=c,c++,fortran --enable-cet --without-isl --enable-libmpx x86_64-linux --disable-bootstrap
> 
> To reproduce:
> 
> $ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/concepts/expression.C --target_board='unix{-m32}'"
> $ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/concepts/expression.C --target_board='unix{-m32\ -march=cascadelake}'"
> $ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/concepts/expression.C --target_board='unix{-m64}'"
> $ cd {build_dir}/gcc && make check RUNTESTFLAGS="dg.exp=g++.dg/concepts/expression.C --target_board='unix{-m64\ -march=cascadelake}'"
> 
> (Please directly reply to this email for question about this report.)
> (If you met problems with cascadelake related, disabling AVX512F in command line might save that.)
> (However, please make sure that there is no potential problems with AVX512.)
Fixed in 786e316de5c25a3fddeaa2003f6efb64fb5ab4a9  2026-02-06 03:25:21

     libstdc++: fix C++17 regression in concept __heterogeneous_key

     The commit 3f7905550483408a2c4c5096a1adc8d7e863eb12 defined a
     concept using a name not defined in C++17. This is fixed by
     using an older name.

     https://gcc.gnu.org/pipermail/gcc-patches/2026-February/707814.html

     libstdc++-v3/ChangeLog
     	* include/bits/stl_function.h (__heterogeneous_key): Use
     	C++17-defined remove_cvref<>::type instead.

Nathan Myers
[email protected]