Modern compilers haven't agreed with you in the last 5 years or so. They definitely assume that if you have 'enum foo' you can only ever assign values defined by that type to the enum and not other values. You have to add explicit (int) casts if you need to treat it as a raw int now. So modern compilers will assume that if you've handled all the defined enum values, there won't be a default case. GCC 4.2 is the only compiler capable of compiling FreeBSD that will trip over this.

Oof, I had read the comment as only being 4.2. I would also remove the comment if GCC 6 still can't cope. I don't know of a good way to achieve @avg's requirement. We could maybe put the return under #ifndef clang but that's kind of ugly.

Not sure that you are correct John:

% cat foo.c
enum foo { a = 1, b = 2, c = 4 };
enum foo x;

void bar(void)
{
	x = a | c;
}
% clang -Wall foo.c -c
% clang -v
clang -v
FreeBSD clang version 8.0.0 (tags/RELEASE_800/final 356365) (based on LLVM 8.0.0)
Target: x86_64-unknown-freebsd13.0
Thread model: posix
InstalledDir: /usr/bin
%