Open Radar

 
Description:
The -Wstrict-prototypes warning from GCC is not implemented in Clang. In C and Objective-C code, many developers mistakenly use ‘()’ for a function or block parameters expecting it to mean “no arguments” where it actually means “unspecified arguments”. This has been an “obsolescent feature” since C89 and ANSI-C.

This leads to type mis-matches, where a block typed ‘void (^)()’ can be passed as a parameter to ‘void (^)(id obj, float f)’ without warning resulting in issues at runtime (unexpected values, EXC_BAD_ACCESS, etc.). There should be a diagnostic when first creating a variable of a function or block type with unspecified arguments.


Steps to reproduce:
Compile (with -Weverything) and run:

int main(int argc, const char *argv[]) {
    void (^block)() = ^(NSInteger arg) {
        printf(“arg = %ld\n”, arg);
    };
    block(42);
    block(-1);
    return 0;
}


Expected Results:
Warning at line 2 (example using GCC’s language; actual wording should be more effective):
  warning: block declaration isn’t a prototype [-Wstrict-prototypes]


Actual Results:
No warnings are generated; logged output is:
arg = 42
arg = 4294967295


Xcode Version/Build & OS X Version/Build:
Xcode 7.0.1 (7A1001)
OS X 10.10.5 (14F27)


Additional Notes:
See also https://llvm.org/bugs/show_bug.cgi?id=20796