[Bug c++/86373] New: Destructor shall not be instantiated in C++17 mode for prvalue

[antoshkka at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86373

            Bug ID: 86373
           Summary: Destructor shall not be instantiated in C++17 mode for
                    prvalue
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: antoshkka at gmail dot com
  Target Milestone: ---

Following program fails to compile in -std=c++17 mode

struct some {
    some() = default;
    ~some() = delete;
};

some foo() {
    return {};
}

More realistic example:

#include <memory>

struct some;
std::unique_ptr<some> f() {
    return {};
}

Output:

/opt/compiler-explorer/gcc-8.1.0/include/c++/8.1.0/bits/unique_ptr.h:79:16:
error: invalid application of 'sizeof' to incomplete type 'some'
  static_assert(sizeof(_Tp)>0,


However [basic.lval] say "The result object of a prvalue is the object
initialized by the prvalue; a prvalue that is used to compute the value of an
operand of an operator or that has type (possibly cv-qualified) void has no
result object."

So looks like std::unique_ptr<some> has no object here, so the destructor shall
not be instantiated.

Clang compiles both of the above examples.