int_plus_one changes program behavior in regards of overflows

[matthiaskrgr]

Summary

int_plus_one suggestions prevent overflows from happening because it removes a potential case where we could run into T::max() + 1

Reproducer

I tried this code:

fn main() {
    dbg!(comp(254));
    dbg!(comp(255)); // overflow/panic

    dbg!(comp_clippyfixed(254));
    dbg!(comp_clippyfixed(255)); // no panic

}

fn comp(x: u8) -> bool {
    1 >= x + 1
}

fn comp_clippyfixed(x: u8) -> bool {
    1 > x 
}

Version

rustc 1.64.0-nightly (0f4bcadb4 2022-07-30)
binary: rustc
commit-hash: 0f4bcadb46006bc484dad85616b484f93879ca4e
commit-date: 2022-07-30
host: x86_64-unknown-linux-gnu
release: 1.64.0-nightly
LLVM version: 14.0.6

Additional Labels

No response

[Jarcho]

If the overflow check is needed it should be using checked_add. The docs could be updated to note this.

[Rudxain]

I agree. checked_add and wrapping_add should be used instead, for explicitness. When people use bare ops, they usually don't think about overflows