Lint to ban impl Trait in parameters

[SUPERCILEX]

Advantage

You can't use the turbofish with parameter impls which makes it strictly less powerful as far as I can tell. This lint should only apply to public items.

Name: impl_trait_in_param_of_pub_fn.

Category

style (or potentially pedantic)

Example

fn foo(t: impl Trait) {}

Could be written as:

fn foo<T: Trait>(t: T) {}

[blyxyas]

@rustbot claim

[blyxyas]

Just to be clear, when you refer to you can't use the turbofish with parameter impl, can you put an example?

[SUPERCILEX]

Sure:

trait A {}

impl A for u32 {}
impl A for u64 {}

fn foo_impl(_a: impl A) {}
fn foo_turbo<AA: A>(_a: AA) {}

fn do_stuff() {
    // foo_impl(0); // Doesn't compile
    // foo_impl::<u32>(0); // Doesn't compile
    foo_impl(0 as u32);
    foo_turbo(0 as u32);
    foo_turbo::<u32>(0);
}

It gets more annoying when people use Option<impl Something> because then when you want to pass in None you have to say None::<Blah> which looks weird IMO. I guess those are both turbofish, so to be more precise I mean turbofish in the function generic position.

[SUPERCILEX]

Woohoo, thanks!

PS: 5ef3cc8#r101419032