===================================================================
@@ -0,0 +1,7 @@
+! { dg-do compile }
+module stuff
+ implicit none
+ type, bind(C) :: junk ! { dg-warning "may be inaccessible by the C companion" }
+ ! Empty!
+ end type junk
+end module stuff
===================================================================
@@ -3592,14 +3592,25 @@ verify_bind_c_derived_type (gfc_symbol *
curr_comp = derived_sym->components;
- /* TODO: is this really an error? */
+ /* Fortran 2003 allows an empty derived type. C99 appears to disallow an
+ empty struct. Section 15.2 in Fortran 2003 states: "The following
+ subclauses define the conditions under which a Fortran entity is
+ interoperable. If a Fortran entity is interoperable, an equivalent
+ entity may be defined by means of C and the Fortran entity is said
+ to be interoperable with the C entity. There does not have to be such
+ an interoperating C entity."
+ */
if (curr_comp == NULL)
{
- gfc_error ("Derived type '%s' at %L is empty",
- derived_sym->name, &(derived_sym->declared_at));
- return FAILURE;
+ gfc_warning ("Derived type '%s' with BIND(C) attribute at %L is empty, "
+ "and may be inaccessible by the C companion processor",
+ derived_sym->name, &(derived_sym->declared_at));
+ derived_sym->ts.is_c_interop = 1;
+ derived_sym->attr.is_bind_c = 1;
+ return SUCCESS;
}
+
/* Initialize the derived type as being C interoperable.
If we find an error in the components, this will be set false. */
derived_sym->ts.is_c_interop = 1;
The attached patch has been built and regression tested on i686-*-freebsd. There were no regression observed with this patch. So, what does it do? Fortran 2003 allows a derived type to be empty. It so happens that one can also add the BIND(C) attribute to the derived type. The simple example is in the empty_derived_type.f90 testcase: ! { dg-do compile } module stuff implicit none type, bind(C) :: junk ! { dg-warning "inaccessible by the C companion" } ! Empty! end type junk end module stuff gfortran currently disallows the above code with troutmask:sgk[203] gfc4x -c po.f90 po.f90:4.82: , bind(C) :: junk ! { dg-warning "inaccessible by the C companion" } 1 Error: Derived type 'junk' at (1) is empty (Side note: The error message above is mangled!) With the attached patch, the error is degraded to a warning, thusly, laptop:kargl[219] gfc4x -c po.f90 po.f90:4.24: type, bind(C) :: junk 1 Warning: Derived type 'junk' with BIND(C) attribute at (1) is empty, and may be inaccessible by the C companion processor So, what's this business about a C companion processor? A structure cannot be empty, laptop:kargl[223] cat k.c #include <stdio.h> int main() { struct junk { // empty! }; struct junk x; printf("Hello, world!\n"); return 0; } laptop:kargl[224] cc -o z k.c laptop:kargl[225] ./z Hello, world! except gcc accepts the invalid code as an extension without warning or error! laptop:kargl[226] cc -o z -pedantic k.c k.c: In function 'main': k.c:8: warning: struct has no members It seems 'pedantic' does not mean that gcc should pedantically follow the C standard. The C code is invalid! /* Invalid. struct contains no member. */ struct junk { // empty! }; /* Valid. struct is nonempty, contains an unnamed member, is not interoperable with Fortran. */ struct junk { int : 0; }; /* Valid. struct is nonempty, contains a named member, is interoperable with Fortran. */ struct junk { int x; }; For more information see http://groups.google.com/group/comp.lang.fortran/browse_frm/thread/5acfb0c37d904e86# 2010-11-10 Steven G. Kargl <kargl@gcc.gnu.org> * symbol.c (verify_bind_c_derived_type): Accept BIND(C) on an empty derived type. 2010-11-10 Steven G. Kargl <kargl@gcc.gnu.org> * gfortran.dg/empty_derived_type.f90: New test. OK for trunk?