llvmbot
commented
1 month ago @llvm/issue-subscribers-clang-frontend
Author: None (jdrouhard)
```cpp
#include <memory>
class Foo {
inline static std::unique_ptr<Foo> instance_;
};
```
See: https://godbolt.org/z/MqMxs9nzr
This fails to compile due to `unique_ptr<T>::~unique_ptr()` (and thus `default_delete<T>::operator()`) being instantiated at the point of the variable declaration (when the class isn't fully defined yet). Since c++23, `unique_ptr` and `default_delete::operator()` are constexpr, but the declaration of the unique_ptr should not attempt to fully instantiate the destructor or std::default_delete<T>::operator() yet. Or at least the above usage pattern should be allowed, as this is a valid pattern for singletons (that aren't Meyers style). Should this fall back to non-constexpr unique_ptr/default_delete?
This fails using both libc++ and libstdc++. gcc and msvc both compile it fine.
```
In file included from test.cpp:1:
In file included from /builds/clang-19.1.0/bin/../include/c++/v1/memory:944:
In file included from /builds/clang-19.1.0/bin/../include/c++/v1/__memory/inout_ptr.h:16:
In file included from /builds/clang-19.1.0/bin/../include/c++/v1/__memory/shared_ptr.h:32:
/builds/clang-19.1.0/bin/../include/c++/v1/__memory/unique_ptr.h:78:19: error: invalid application of 'sizeof' to an incomplete type 'Foo'
78 | static_assert(sizeof(_Tp) >= 0, "cannot delete an incomplete type");
| ^~~~~~~~~~~
/builds/clang-19.1.0/bin/../include/c++/v1/__memory/unique_ptr.h:292:7: note: in instantiation of member function 'std::default_delete<Foo>::operator()' requested here
292 | __ptr_.second()(__tmp);
| ^
/builds/clang-19.1.0/bin/../include/c++/v1/__memory/unique_ptr.h:261:71: note: in instantiation of member function 'std::unique_ptr<Foo>::reset' requested here
261 | _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX23 ~unique_ptr() { reset(); }
| ^
simple.cpp:4:38: note: in instantiation of member function 'std::unique_ptr<Foo>::~unique_ptr' requested here
4 | inline static std::unique_ptr<Foo> instance;
| ^
simple.cpp:3:7: note: definition of 'Foo' is not complete until the closing '}'
3 | class Foo {
```
zyn0217
See: https://godbolt.org/z/MqMxs9nzr
This fails to compile due to::operator() yet. Or at least the above usage pattern should be allowed, as this is a valid pattern for singletons (that aren't Meyers style). Should this fall back to non-constexpr unique_ptr/default_delete?
unique_ptr<T>::~unique_ptr()(and thusdefault_delete<T>::operator()) being instantiated at the point of the variable declaration (when the class isn't fully defined yet). Since c++23,unique_ptranddefault_delete::operator()are constexpr, but the declaration of the unique_ptr should not attempt to fully instantiate the destructor or std::default_deleteThis fails using both libc++ and libstdc++. gcc and msvc both compile it fine.