__is_trivial doesn't work in the presence of special member functions with trailing requires clauses #50084
Comments
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I'm not a Clang expert, but I think CXXRecordDecl::addedMember() is incorrectly setting up this declaration: as a special member function that is non-trivial and user-provided, even though should (?) not be considered because of the trailing requires clause. |
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This is part of P0848R3, which we don't yet implement. |
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Oh, thanks, I thought http://wg21.link/P0848 was just adding the trailing requires clauses to constructors with that use case in mind, but I had it wrong. So this is simply not implemented. I guess we can close as INVALID, since this is not a bug, merely a missing feature. |
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Extended Description
When compiled with Clang ToT, the following code incorrectly believes that allocator is non-trivial, when it should be trivial:
cat <<EOF | clang++ -xc++ - -std=c++2a -fsyntax-only
#include <type_traits>
template
struct allocator {
allocator() = default;
allocator() requires(!std::is_void_v) { }
};
static_assert(__is_trivial(allocator));
int main() { }
EOF
This works on GCC. Godbolt link: https://godbolt.org/z/4osMGWTne.
I tracked the issue down a bit, and I think the issue is that when QualType::isTrivialType() queries whether the class declaration has a non-trivial default constructor (via CXXRecordDecl::hasNonTrivialDefaultConstructor()), it incorrectly believes that it's the case.
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