https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117560
Bug ID: 117560
Summary: std::views::zip incompatible with
std::filesystem::directory_iterator &
std::views::transform
Product: gcc
Version: 14.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: ralph.ursprung at gmail dot com
Target Milestone: ---
Created attachment 59588
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59588&action=edit
test case reproducing the error
the attached code compiles fine with MSVC (tested on Windows 11 x64 with
17.12.0 but also worked before with previous 17.11.x and possibly older
releases) and LLVMs libc++ (tested on Ubuntu 24.04 LTS with 18.1.3) but fails
with GCCs libstdc++ (tested with GCC/libstdc++ 14.2.0).
this is a problem in the standard library implementation and not the compiler
as clang fails with the same compile error as GCC when using libstdc++ but
works fine when using its own library.
i have narrowed it down to the combination of
`std::filesystem::directory_iterator`, `std::views::transform` and
`std::views::zip` (though others might of course be affected! i just reduced my
real-world problem to this test-case).
you can get the code to compile by removing the `| std::views::transform(t)`
from the two variables `x1` & `x2` in the test case or by replacing
`std::filesystem::directory_iterator{p}` with `std::views::empty`
(or something similarly simple, e.g.
`std::views::single(std::string{"hello"})`).
error using GCC:
> $ g++-14 -std=c++23 -Wall -Wextra filesystem-fail.cpp && ./a.out
> filesystem-fail.cpp: In function ‘int main()’:
> filesystem-fail.cpp:15:46: error: no match for call to ‘(const
> std::ranges::views::_Zip)
> (std::ranges::transform_view,
> main():: >&,
> std::ranges::transform_view,
> main():: >&)’
>15 | for (auto const& [f1, f2] : std::views::zip(x1, x2)) {
> | ~~~^~~~
> In file included from filesystem-fail.cpp:3:
> /usr/include/c++/14/ranges:4969:9: note: candidate: ‘template
> requires sizeof ... (_Ts ...) == 0 || (__can_zip_view<_Ts ...>) constexpr
> auto std::ranges::views::_Zip::operator()(_Ts&& ...) const’
> 4969 | operator() [[nodiscard]] (_Ts&&... __ts) const
> | ^~~~
> /usr/include/c++/14/ranges:4969:9: note: template argument
> deduction/substitution failed:
> /usr/include/c++/14/ranges:4969:9: note: constraints not satisfied
> filesystem-fail.cpp: In substitution of ‘template requires
> sizeof ... (_Ts ...) == 0 || (__can_zip_view<_Ts ...>) constexpr auto
> std::ranges::views::_Zip::operator()(_Ts&& ...) const [with _Ts =
> {std::ranges::transform_view,
> main():: >&,
> std::ranges::transform_view,
> main():: >&}]’:
> filesystem-fail.cpp:15:46: required from here
>15 | for (auto const& [f1, f2] : std::views::zip(x1, x2)) {
> | ~~~^~~~
> /usr/include/c++/14/ranges:4969:2: required by the constraints of
> ‘template requires sizeof ... (_Ts ...) == 0 ||
> (__can_zip_view<_Ts ...>) constexpr auto
> std::ranges::views::_Zip::operator()(_Ts&& ...) const’
> /usr/include/c++/14/ranges:4967:39: note: no operand of the disjunction is
> satisfied
> 4967 | requires (sizeof...(_Ts) == 0 ||
> __detail::__can_zip_view<_Ts...>)
> |
> ~^~~~
> cc1plus: note: set ‘-fconcepts-diagnostics-depth=’ to at least 2 for more
> detail
GCC version:
> $ g++-14 -v
> Using built-in specs.
> COLLECT_GCC=g++-14
> COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-linux-gnu/14/lto-wrapper
> OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
> OFFLOAD_TARGET_DEFAULT=1
> Target: x86_64-linux-gnu
> Configured with: ../src/configure -v --with-pkgversion='Ubuntu
> 14.2.0-4ubuntu2~24.04' --with-bugurl=file:///usr/share/doc/gcc-14/README.Bugs
> --enable-languages=c,ada,c++,go,d,fortran,objc,obj-c++,m2,rust --prefix=/usr
> --with-gcc-major-version-only --program-suffix=-14
> --program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
> --libexecdir=/usr/libexec --without-included-gettext --enable-threads=posix
> --libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
> --enable-libstdcxx-debug --enable-libstdcxx-time=yes
> --with-default-libstdcxx-abi=new --enable-libstdcxx-backtrace
> --enable-gnu-unique-object --disable-vtable-verify --enable-plugin
> --enable-default-pie --with-system-zlib --enable-libphobos-checking=release
> --with-target-system-zlib=auto --enable-objc-gc=auto --enable-multiarch
> --disable-werror --enable-cet --with-arch-32=i686 --with-abi=m64
> --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic
> --enable-offload-targets=nvptx-none=/build/gcc-14-ig5ci0/gcc-14-14.2
