Avoid false-positive -Wswitch warnings

Question

Let's have a list of values (foo.lst):

foo,
bar,
baz,

Let's make an enum out of this

enum foo {
  #include "foo.lst"
  _foo_length
};

Let's use that enum in a switch:

int main(void) {
  enum foo[_foo_length];

  switch(f[0]) {
    case foo: return 0;
    case bar: return 0;
    case baz: return 0;
  }

  __builtin_unreachable();
}

(this code is dumb, but just ignore that)

The problem:
With -Wswitch (included in -Wall), GCC and Clang (and probably others) will warn:

warning: enumeration value '_foo_length' not handled in switch [-Wswitch]

Solutions:

• Disabling -Wno-switch hides that warning.
  Downside: we lose warnings about any other case missing from the switch.
• Adding a default: unreachable(); case.
  Downside: we lose compile-time warnings of missing cases, in favour of a runtime crash if we ever hit one of the missing cases when debugging.
• Replacing the last value of the enum with a #define _foo_length (baz + 1), making it not part of the enum anymore.
  Downside: it requires that define to be manually updated every time a value is added to the list. Someone will invariably forget, breaking everything.

Ideally, there should be a way to mark an enum's value as no being assignable, thereby making it not produce a warning in the compiler when reading the possible values and this one isn't there, without requiring a preprocessor macro needing duplicate modifications.

Is there anything like that? Any other option I didn't think of?

Answer 1

Use

case _foo_length:
    unreachable();
    break;

so that all the cases will be handled. You could create a macro for it to keep it from being so verbose.