https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97449
Bug ID: 97449
Summary: libstdc++ <variant> cannot be compiled with clang
after 3427e31331677ca826c5588c87924214f7e5c54b
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
Assignee: unassigned at gcc dot gnu.org
Reporter: foom at fuhm dot net
Target Milestone: ---
After 3427e31331677ca826c5588c87924214f7e5c54b, "clang -std=c++17" (using
libstdc++ headers), on a file that has simply "#include <variant>" fails with
this error:
In file included from <source>:1:
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/11.0.0/../../../../include/c++/11.0.0/variant:1032:10:
error: no matching constructor for initialization of 'std::__nonesuch'
return __nonesuch{};
^ ~~
/opt/compiler-explorer/gcc-snapshot/lib/gcc/x86_64-linux-gnu/11.0.0/../../../../include/c++/11.0.0/type_traits:2953:5:
note: candidate constructor not viable: requires 1 argument, but 0 were
provided
__nonesuch(__nonesuch const&) = delete;
^
(https://godbolt.org/z/951jYr)
I believe Clang is correct to reject this code, due to
http://eel.is/c++draft/temp.res#general-8.1
"""
The program is ill-formed, no diagnostic required, if:
- no valid specialization can be generated for a template or a substatement of
a constexpr if statement within a template and the template is not instantiated
"""
The invalid return statement probably needs to be made dependent on
__visit_ret_type_mismatch just like the static_assert.
