New lint: multiple-bound-locations

[nico-abram]

What it does

Checks for generic functions that have bounds for a generic parameter in both a where clause and the parameter list

Categories (optional)

• Kind: pedantic

What is the advantage of the recommended code over the original code

It makes the code less confusing, having bounds in multiple places makes it easy to miss one half. Specially if it's something small, for example (From nom documentation), here it is very easy to miss the : 'a bound on F

fn ws<'a, F: 'a, O, E: ParseError<&'a str>>(
    inner: F,
) -> impl FnMut(&'a str) -> IResult<&'a str, O, E>
where
    F: Fn(&'a str) -> IResult<&'a str, O, E>,
{
    delimited(
        nom::character::complete::multispace0,
        inner,
        nom::character::complete::multispace0,
    )
}

Drawbacks

None.

Example

fn f<'a, T: 'a>(x:T) where T: FnOnce() { x(); }

Could be written as:

fn f<'a, T>(x:T) where T: FnOnce() + 'a { x(); }