Removing bound from generic type causes an "overflow evaluating a requirement" error.

[rodrimati1992]

With the following code:

pub trait Frogg<W: ?Sized> {
    fn frogg(&self, _with: &W){}
}

impl <T, W> Frogg<[W]> for T
where
    T: Frogg<W>
{}

impl <T, W> Frogg<[W]> for [T]
where
    T: Frogg<W>
{}

fn bar<T, W>(slice: &[T], other: &[W]) 
where
    T:Frogg<W>
{
    slice.frogg(other)
}

If I remove the where clause for bar,it prints this error:

error[E0275]: overflow evaluating the requirement `_: std::marker::Sized`
  --> src/lib.rs:16:11
   |
16 |     slice.frogg(other)
   |           ^^^^^
   |
   = help: consider adding a `#![recursion_limit="256"]` attribute to your crate
   = note: required because of the requirements on the impl of `Frogg<[_]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[_]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[_]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[_]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[_]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[_]]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[[_]]]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[[[_]]]]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[[[[_]]]]]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[[[[[_]]]]]]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[[[[[[_]]]]]]]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[[[[[[[_]]]]]]]]]]]]>` for `T`
   = note: required because of the requirements on the impl of `Frogg<[[[[[[[[[[[[[_]]]]]]]]]]]]]>` for `T`
   [Ommited identical errors for length]

error: aborting due to previous error

I expected to get an error mentioning how slice does not implement the Frogg trait instead.

[Centril]

cc @rust-lang/wg-traits

[istankovic]

I think this can be closed since the error is much better now:

   Compiling playground v0.0.1 (/playground)
error[E0275]: overflow evaluating the requirement `_: Sized`
  --> src/lib.rs:18:11
   |
18 |     slice.frogg(other)
   |           ^^^^^
   |
   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`playground`)
note: required for `T` to implement `Frogg<[_]>`
  --> src/lib.rs:5:13
   |
5  | impl <T, W> Frogg<[W]> for T
   |          -  ^^^^^^^^^^     ^
   |          |
   |          unsatisfied trait bound introduced here
   = note: 128 redundant requirements hidden
   = note: required for `[T]` to implement `Frogg<[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[_]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]>`

For more information about this error, try `rustc --explain E0275`.
error: could not compile `playground` (lib) due to previous error