`manual_div_ceil` does not trigger for alternate form

[ronnodas]

Summary

The lint triggers for expressions of the form (a + b - 1) / b but not of the form (a - 1) / b + 1. For unsigned integers, these are equivalent ignoring overflow/underflow.

Lint Name

manual_div_ceil

Reproducer

I tried this code (playground):

fn div_ceil(a: u32, b: u32) -> u32 {
    (a - 1) / b + 1
}

I expected to see this happen:
The manual_div_ceil lint should trigger, suggesting a.div_ceil(b).

Instead, this happened:
Nothing.

[Gri-ffin]

the two expressions arent equivalent in all cases since rust division truncates towards zero for signed ints, take the case of a = -1, and b = 4. we get 0 for both the first expression and div_ceil but 1 for the second.

[ronnodas]

@Gri-ffin thanks, edited to specify a and b unsigned.