While analyzing PR100154, Tobias pointed me to the following:

F2018:R902: function-reference shall have a data pointer result

A variable is either the data object denoted by designator or the target of the pointer resulting from the evaluation of function-reference; this pointer shall
be associated.

He also gave an example in that other PR, for which I have a fix.  In my
interpretation the following code should thus also be valid and is accepted
by two other compilers I tested (Intel, Nvidia) and gives the right result.

program p
  implicit none
  integer, target :: z = 0
  call g (f ())
  print *, z
contains
  function f () result (r)
    integer, pointer :: r
    r => z
  end function f
  subroutine g (x)
    integer, intent(out) :: x
    x = 1
  end subroutine g
end program p


The following patch seems to help:

diff --git a/gcc/fortran/expr.c b/gcc/fortran/expr.c
index 92a6700568d..696b9f1daac 100644
--- a/gcc/fortran/expr.c
+++ b/gcc/fortran/expr.c
@@ -6121,7 +6132,9 @@ gfc_check_vardef_context (gfc_expr* e, bool pointer, bool alloc_obj,
     }
   if (!pointer && sym->attr.flavor != FL_VARIABLE
       && !(sym->attr.flavor == FL_PROCEDURE && sym == sym->result)
-      && !(sym->attr.flavor == FL_PROCEDURE && sym->attr.proc_pointer))
+      && !(sym->attr.flavor == FL_PROCEDURE && sym->attr.proc_pointer)
+      && !(sym->attr.flavor == FL_PROCEDURE
+	   && sym->attr.function && sym->attr.pointer))
     {
       if (context)
 	gfc_error ("%qs in variable definition context (%s) at %L is not"