[llvm-bugs] [Bug 32978] New: Cannot create shared_ptr of types with noexcept(false) destructor

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https://bugs.llvm.org/show_bug.cgi?id=32978

            Bug ID: 32978
           Summary: Cannot create shared_ptr of types with noexcept(false)
                    destructor
           Product: libc++
           Version: unspecified
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: All Bugs
          Assignee: unassignedclangbugs at nondot.org
          Reporter: marvin_schmidt at gmx.net
                CC: llvm-bugs at lists.llvm.org, mclow.lists at gmail.com

Created attachment 18422
  --> https://bugs.llvm.org/attachment.cgi?id=18422&action=edit
patch to fix `make_shared<T>()` for types with noexcept(false) dtors

Hey folks,

I'm not sure if this is a bug in libc++ or not. But it's something, where
libstdc++ and libc++ behave differently. With libc++ calling
std::make_shared<T>() where T has a destructor marked `noexcept(false)` fails
to compile.

Test case:

#include <memory>

struct Foo
{
        Foo() = default;
        ~Foo() noexcept(false) { throw 42; }
};

int main()
{
        auto ptr = std::make_shared<Foo>();
        return 0;
}


fails to compile with the following error:

# clang++ -std=c++11 -stdlib=libc++ -Wall -pedantic -O0 -o test test.cc
In file included from test.cc:1:
/usr/x86_64-pc-linux-gnu/bin/../include/c++/v1/memory:3589:7: error: exception
specification of overriding function is more lax than base version
class __shared_ptr_emplace
      ^
/usr/x86_64-pc-linux-gnu/bin/../include/c++/v1/memory:4228:26: note: in
instantiation of template class 'std::__1::__shared_ptr_emplace<Foo,
std::__1::allocator<Foo> >' requested here
    ::new(__hold2.get()) _CntrlBlk(__a2, _VSTD::forward<_Args>(__args)...);
                         ^
/usr/x86_64-pc-linux-gnu/bin/../include/c++/v1/memory:4598:29: note: in
instantiation of function template specialization
'std::__1::shared_ptr<Foo>::make_shared<>' requested here
    return shared_ptr<_Tp>::make_shared(_VSTD::forward<_Args>(__args)...);
                            ^
test.cc:11:25: note: in instantiation of function template specialization
'std::__1::make_shared<Foo>' requested here
        auto ptr = std::make_shared<Foo>();
                        ^
/usr/x86_64-pc-linux-gnu/bin/../include/c++/v1/memory:3498:13: note: overridden
virtual function is here
    virtual ~__shared_weak_count();
            ^
1 error generated.


The attached patch fixes that by marking the destructors of
__shared_ptr_emplace, __shared_{,weak_}count with _NOEXCEPT, but I'm not sure,
if this is the way to go. It also is not a complete fix, since the
std::locale::facet for example is also derived from __shared_count and would
need to be adjusted accordingly as well.
I appreciate any insights on this

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