#[derive] generates unnecessary bound when field is associated type

[durka]

With this struct:

#[derive(Debug)]
struct Foo<T: std::str::FromStr> {
    field: T::Err,
}

The only bound needed on the generated impl is where T::Err: Debug. However, the generated code contains where T: Debug, T::Err: Debug. Why is the first one necessary? The deriving code already scans the field types to find T::Err so it should be able to see that bare T is not mentioned.

cc #26925

[fmease]

This is simply an instance of #26925 (Ctrl+F for assoc, perfect deriving, T::, etc.) which you've already cc'ed. Closing as duplicate of it.