rustfmt removes GATs from associated type

[louaykamel]

I tried this code:

#![feature(generic_associated_types)]

trait GAT {
    type R<T>;
    fn do_something<T>(r: Self::R<T>) -> Self::R<T> {
        r
    }
    
}
struct SomeStruct;

impl GAT for SomeStruct {
    type R<T> = T;
}

impl SomeStruct {
    fn process<T>(v: T) -> <Self as GAT>::R<T>
    // Issue: rustfmt removes the GAT from the associated R  
    where Self: GAT<R<T> = T>
    {
        SomeStruct::do_something(v)
    }
}


fn main() {
  let one: u8 = SomeStruct::process(1);
  assert!(one == 1)
}

I expected rustfmt to: keep <T>

where Self: GAT<R<T> = T>

Instead, this happened: removed <T>

where Self: GAT<R = T>

Meta

rustc --version --verbose:

rustc 1.56.0-nightly (2f07ae408 2021-08-05)
binary: rustc
commit-hash: 2f07ae408fce782bf1058e3de808f1b6f9ab60a4
commit-date: 2021-08-05
host: x86_64-unknown-linux-gnu
release: 1.56.0-nightly
LLVM version: 12.0.1

[louaykamel]

#4911