[Bug fortran/103931] Type name "c_ptr" is ambiguous when iso_c_binding is imported both directly and indirectly

["anlauf at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103931

--- Comment #20 from anlauf at gcc dot gnu.org ---
(In reply to Bernhard Reutner-Fischer from comment #18)
> diff --git a/gcc/fortran/symbol.cc b/gcc/fortran/symbol.cc
> index 221165d6dac..28ed1a32b9e 100644
> --- a/gcc/fortran/symbol.cc
> +++ b/gcc/fortran/symbol.cc
> @@ -4977,6 +4986,10 @@ generate_isocbinding_symbol (const char *mod_name,
> iso_c_binding_symbol s,
>  	      if (!tmp_sym->attr.function
>  		  && !gfc_add_function (&tmp_sym->attr, tmp_sym->name, NULL))
>  		return NULL;
> +
> +	      /* Mark the derived-type symbol in the generic interface
> +	         as generic.  */
> +	      dt_sym->attr.generic = 1;
>  	    }
>  
>  	  /* Say what module this symbol belongs to.  */
> 
> 

This change would lead to an accepts-invalid, such as for:

module AModule
  use, intrinsic :: ISO_C_BINDING, only: C_PTR
  use, intrinsic :: ISO_C_BINDING, only: X_PTR => C_FUNPTR
  implicit none
end module

module GModule
  use AModule, only: X_PTR => C_PTR ! C_PTR
  implicit none
end module

module HModule
  use AModule, only: C_PTR => X_PTR ! C_FUNPTR
  use GModule, only: C_PTR => X_PTR ! C_PTR
  implicit none
  type(c_ptr) :: ptr
end module

Without the patch I'd get (as expected):

pr103931-v3.f90:16:14:

   16 |   type(c_ptr) :: ptr
      |              1
Error: Type name 'c_ptr' at (1) is ambiguous

With the patch the actual type of ptr depends on the order of the use
statements in HModule - at least this is what the fortran-dump says...