gcc/testsuite/objc.dg/class-2.m

/* Test super classes.  */
/* { dg-do compile } */

@interface supclass1
@end

@interface supclass2
@end

@interface class1 : supclass1
@end

@implementation class1 : supclass2 /* { dg-error "conflicting super class name" } */
@end /* { dg-error "previous declaration" "" { target *-*-* } .-1 } */