[Bug c++/114210] New: Potential bug wrt __restrict on member function decl/def

[rl.alt.accnt at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114210

            Bug ID: 114210
           Summary: Potential bug wrt __restrict on member function
                    decl/def
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rl.alt.accnt at gmail dot com
  Target Milestone: ---

Clang dev here; I’m currently working on improving our support for `__restrict`
in the cv-qualifier-seq of member functions, and I have a question about the
following situation:

struct S {
    void a() __restrict;
    void b();
};

void S::a() { static_assert(__is_same(decltype(this), S*)); }
void S::b() __restrict { 
    static_assert(__is_same(decltype(this), S* __restrict)); 
}

`decltype(this)` is `S* __restrict` in the body of `S::b`, but `S*` (no
`__restrict`) in the body of `S::a`, i.e. GCC only seems to care about
`__restrict` being present in the definition, not the declaration. 

According to the documentation
(https://gcc.gnu.org/onlinedocs/gcc-13.2.0/gcc/Restricted-Pointers.html), ‘you
only need to specify __restrict__ in a function definition, rather than in a
function prototype as well.’ This doesn’t
really say anything about what happens if the opposite is the case (i.e. if
`__restrict` is only present in the declaration, not the definition).

My question, then: is this intended, or is it a bug?