[Bug c++/66832] New: [concepts] parameters in requires clauses conflicting with function arguments

[eric.niebler at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66832

            Bug ID: 66832
           Summary: [concepts] parameters in requires clauses conflicting
                    with function arguments
           Product: gcc
           Version: c++-concepts
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eric.niebler at gmail dot com
  Target Milestone: ---

template <class T, class U, unsigned N>
  requires requires (T& t, U &u) { t.foo(); u.foo(); }
void foo_all( T (&t)[N], U (&u)[N] ) {
  for(auto& x : t)
      x.foo();
  for(auto& x : u)
      x.foo();
}

struct S {
  void foo() {}
};

int main() {
  S rg[4] {};
  foo_all(rg, rg);
}


Yields:

/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp:4:23: error: conflicting
declaration ‘T (& t)[N]’
 void foo_all( T (&t)[N], U (&u)[N] ) {
                       ^
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp:3:25: note: previous
declaration as ‘T& t’
   requires requires (T& t, U &u) { t.foo(); u.foo(); }
                         ^
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp: In function ‘void
foo_all(U (&)[N])’:
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp:5:18: error: use of
parameter outside function body before ‘)’ token
   for(auto& x : t)
                  ^
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp: In function ‘int
main()’:
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp:17:17: error: no matching
function for call to ‘foo_all(S [4], S [4])’
   foo_all(rg, rg);
                 ^
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp:4:6: note: candidate:
template<class T, class U, unsigned int N>  requires predicate(r
equires(T& t, U& u) {t->foo();u->foo();}) void foo_all(U (&)[N])
 void foo_all( T (&t)[N], U (&u)[N] ) {
      ^
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp:4:6: note:   template
argument deduction/substitution failed:
/cygdrive/c/Users/eric/Code/cmcstl2/test/iterator.cpp:17:17: note:   candidate
expects 1 argument, 2 provided
   foo_all(rg, rg);
                 ^