llvm-project/clang/test/Analysis/ObjCRetSigs.m

// RUN: clang -analyze -warn-objc-methodsigs -verify %s

#include <stdio.h>

@interface MyBase
-(long long)length;
@end

@interface MySub : MyBase{}
-(double)length;
@end

@implementation MyBase
-(long long)length{
   printf("Called MyBase -length;\n");
   return 3;
}
@end

@implementation MySub
-(double)length{  // expected-warning{{types are incompatible}}
   printf("Called MySub -length;\n");
   return 3.3;
}
@end