https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115939
Bug ID: 115939
Summary: Cannot unambiguously compare iterators in
std::unordered_map with mapped type
std::expected<std::any, Y>>
Product: gcc
Version: 14.1.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: halfflat at gmail dot com
Target Milestone: ---
Created attachment 58667
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=58667&action=edit
Preprocessed .ii file from example code
Consider the following code:
#include <any>
#include <expected>
#include <unordered_map>
struct Y {};
std::unordered_map<int, std::expected<std::any, Y>> m;
bool r = m.begin()==m.end();
When compiled with g++ -c -std=c++23 -pedantic we get an "ambiguous overload
for ‘operator==’" error. This issue has been replicated on Compiler Explorer
(https://godbolt.org/z/cqoedqKbr). It is not clear to me if this results from a
fundamental issue in the standard library specification or is a consequence of
the implementation in libstdc++.
The original context of the bug was in code that was attempting to use a
std::unordered_map<std::type_index, std::function<std::expected<std::any,
failure> (std::string_view)>> (where failure was a separately defined type).
Compiler output below:
% g++ -v -save-temps -c -std=c++23 -pedantic bug.cc
Using built-in specs.
COLLECT_GCC=g++
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure
--enable-languages=ada,c,c++,d,fortran,go,lto,m2,objc,obj-c++,rust
--enable-bootstrap --prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib
--mandir=/usr/share/man --infodir=/usr/share/info
--with-bugurl=https://gitea.artixlinux.org/packages/gcc/issues
--with-build-config=bootstrap-lto --with-linker-hash-style=gnu
--with-system-zlib --enable-__cxa_atexit --enable-cet=auto
--enable-checking=release --enable-clocale=gnu --enable-default-pie
--enable-default-ssp --enable-gnu-indirect-function --enable-gnu-unique-object
--enable-libstdcxx-backtrace --enable-link-serialization=1
--enable-linker-build-id --enable-lto --enable-multilib --enable-plugin
--enable-shared --enable-threads=posix --disable-libssp --disable-libstdcxx-pch
--disable-werror
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 14.1.1 20240507 (GCC)
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-std=c++23' '-Wpedantic'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/cc1plus -E -quiet -v -D_GNU_SOURCE
bug.cc -mtune=generic -march=x86-64 -std=c++23 -Wpedantic -fpch-preprocess -o
bug.ii
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/../../../../x86_64-pc-linux-gnu/include"
ignoring nonexistent directory "/home/sam/pkg/include"
#include "..." search starts here:
#include <...> search starts here:
/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/../../../../include/c++/14.1.1
/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/../../../../include/c++/14.1.1/x86_64-pc-linux-gnu
/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/../../../../include/c++/14.1.1/backward
/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/include
/usr/local/include
/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/include-fixed
/usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-c' '-std=c++23' '-Wpedantic'
'-shared-libgcc' '-mtune=generic' '-march=x86-64'
/usr/lib/gcc/x86_64-pc-linux-gnu/14.1.1/cc1plus -fpreprocessed bug.ii -quiet
-dumpbase bug.cc -dumpbase-ext .cc -mtune=generic -march=x86-64 -Wpedantic
-std=c++23 -version -o bug.s
GNU C++23 (GCC) version 14.1.1 20240507 (x86_64-pc-linux-gnu)
compiled by GNU C version 14.1.1 20240507, GMP version 6.3.0, MPFR
version 4.2.1, MPC version 1.3.1, isl version isl-0.26-GMP
GGC heuristics: --param ggc-min-expand=100 --param ggc-min-heapsize=131072
Compiler executable checksum: 79593118236b8aa0b562fa91bdea97d6
bug.cc:7:19: error: ambiguous overload for ‘operator==’ (operand types are
‘std::unordered_map<int, std::expected<std::any, Y> >::iterator’ {aka
‘std::__detail::_Insert_base<int, std::pair<const int, std::expected<std::any,
Y> >, std::allocator<std::pair<const int, std::expected<std::any, Y> > >,
std::__detail::_Select1st, std::equal_to<int>, std::hash<int>,
std::__detail::_Mod_range_hashing, std::__detail::_Default_ranged_hash,
std::__detail::_Prime_rehash_policy, std::__detail::_Hashtable_traits<false,
false, true> >::iterator’} and ‘std::unordered_map<int, std::expected<std::any,
Y> >::iterator’ {aka ‘std::__detail::_Insert_base<int, std::pair<const int,
std::expected<std::any, Y> >, std::allocator<std::pair<const int,
std::expected<std::any, Y> > >, std::__detail::_Select1st, std::equal_to<int>,
std::hash<int>, std::__detail::_Mod_range_hashing,
std::__detail::_Default_ranged_hash, std::__detail::_Prime_rehash_policy,
std::__detail::_Hashtable_traits<false, false, true> >::iterator’})
7 | bool r = m.begin()==m.end();
| ~~~~~~~~~^~~~~~~~~
| | |
| | _Node_iterator<[...],[...],[...]>
| _Node_iterator<[...],[...],[...]>
In file included from bug.cc:2:
/usr/include/c++/14.1.1/expected:1133:9: note: candidate: ‘constexpr bool
std::operator==(const expected<_Tp, _Er>&, const _Up&) [with _Up =
__detail::_Node_iterator<pair<const int, expected<any, Y> >, false, false>; _Tp
= any; _Er = Y]’ (reversed)
1133 | operator==(const expected& __x, const _Up& __v)
| ^~~~~~~~
In file included from /usr/include/c++/14.1.1/bits/hashtable.h:35,
from /usr/include/c++/14.1.1/bits/unordered_map.h:33,
from /usr/include/c++/14.1.1/unordered_map:41,
from bug.cc:3:
/usr/include/c++/14.1.1/bits/hashtable_policy.h:407:7: note: candidate: ‘bool
std::__detail::operator==(const _Node_iterator_base<std::pair<const int,
std::expected<std::any, Y> >, false>&, const
_Node_iterator_base<std::pair<const int, std::expected<std::any, Y> >,
false>&)’
407 | operator==(const _Node_iterator_base& __x, const
_Node_iterator_base& __y)
| ^~~~~~~~
