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<std::string>`
(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<std::ranges::owning_view<std::filesystem::__cxx11::directory_iterator>,
> main()::<lambda(const std::filesystem::__cxx11::directory_entry&)> >&,
> std::ranges::transform_view<std::ranges::owning_view<std::filesystem::__cxx11::directory_iterator>,
> main()::<lambda(const std::filesystem::__cxx11::directory_entry&)> >&)’
> 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<class ... _Ts>
> 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<class ... _Ts> requires
> sizeof ... (_Ts ...) == 0 || (__can_zip_view<_Ts ...>) constexpr auto
> std::ranges::views::_Zip::operator()(_Ts&& ...) const [with _Ts =
> {std::ranges::transform_view<std::ranges::owning_view<std::filesystem::__cxx11::directory_iterator>,
> main()::<lambda(const std::filesystem::__cxx11::directory_entry&)> >&,
> std::ranges::transform_view<std::ranges::owning_view<std::filesystem::__cxx11::directory_iterator>,
> main()::<lambda(const std::filesystem::__cxx11::directory_entry&)> >&}]’:
> 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<class ... _Ts> 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-14-14.2.0/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-14-ig5ci0/gcc-14-14.2.0/debian/tmp-gcn/usr
> --enable-offload-defaulted --without-cuda-driver --enable-checking=release
> --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
> --with-build-config=bootstrap-lto-lean --enable-link-serialization=2
> Thread model: posix
> Supported LTO compression algorithms: zlib zstd
> gcc version 14.2.0 (Ubuntu 14.2.0-4ubuntu2~24.04)
error using LLVM:
> $ clang++-18 -std=c++23 -Wall -Wextra filesystem-fail.cpp
> filesystem-fail.cpp:15:31: error: no matching function for call to object of
> type 'const _Zip'
> 15 | for (auto const& [f1, f2] : std::views::zip(x1, x2)) {
> | ^~~~~~~~~~~~~~~
> /usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/ranges:4969:2:
> note: candidate template ignored: constraints not satisfied [with _Ts =
> <transform_view<views::all_t<directory_iterator>, (lambda at
> filesystem-fail.cpp:9:18)> &,
> transform_view<views::all_t<directory_iterator>, (lambda at
> filesystem-fail.cpp:9:18)> &>]
> 4969 | operator() [[nodiscard]] (_Ts&&... __ts) const
> | ^
> /usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/ranges:4967:12:
> note: because 'sizeof...(_Ts) == 0' (2 == 0) evaluated to false
> 4967 | requires (sizeof...(_Ts) == 0 ||
> __detail::__can_zip_view<_Ts...>)
> | ^
> /usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/ranges:4967:35:
> note: and
> '__detail::__can_zip_view<std::ranges::transform_view<std::ranges::owning_view<std::filesystem::directory_iterator>,
> (lambda at filesystem-fail.cpp:9:18)> &,
> std::ranges::transform_view<std::ranges::owning_view<std::filesystem::directory_iterator>,
> (lambda at filesystem-fail.cpp:9:18)> &>' evaluated to false
> 4967 | requires (sizeof...(_Ts) == 0 ||
> __detail::__can_zip_view<_Ts...>)
> | ^
> /usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/ranges:4961:26:
> note: because 'zip_view<all_t<_Ts>...>(std::declval<_Ts>()...)' would be
> invalid: constraints not satisfied for alias template 'all_t' [with _Range =
> std::ranges::transform_view<std::ranges::owning_view<std::filesystem::directory_iterator>,
> (lambda at filesystem-fail.cpp:9:18)> &]
> 4961 | = requires {
> zip_view<all_t<_Ts>...>(std::declval<_Ts>()...); };
> | ^
> 1 error generated.
with `clang++-18 -std=c++23 -stdlib=libc++ -Wall -Wextra filesystem-fail.cpp`
it works fine (note the switch to libc++).
clang version:
> $ clang++-18 -v
> Ubuntu clang version 18.1.8
> (++20240731024944+3b5b5c1ec4a3-1~exp1~20240731145000.144)
> Target: x86_64-pc-linux-gnu
> Thread model: posix
> InstalledDir: /usr/bin
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/11
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/13
> Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/14
> Selected GCC installation: /usr/bin/../lib/gcc/x86_64-linux-gnu/14
> Candidate multilib: .;@m64
> Selected multilib: .;@m64
