Example code which triggers the assert, but emits no warnings from Cargo or Clippy in pedantic mode:

#[deny(clippy::pedantic)]
pub fn main() {
    let x: usize = 65_535;

    // Should be u16::MAX
    if x < u16::max as usize {
        println!("fits in a u16!");
        assert!(x < 65_535);
    } else {
        println!("Too big!");
    }
}

Although clippy::fn_to_numeric_cast_any will catch this mistake, it's not enabled in pedantic mode and will flag all other uses where function pointers are converted to integers.

Possible solutions:

• Enable clippy::fn_to_numeric_cast_any by default for the special case of standard library functions where associated constants and functions are lookalikes.
• Warn when function pointers are cast to usize in a non-equality comparison.

I don't think we can make fn_to_numeric_cast_any to be emitted in some special cases. Its category cannot be changed at runtime.

I think in this case, the best might be a specialized new lint. Something like primitive_method_to_numeric_cast.