`where` clauses in GAT impls aren't formatted

[clarfonthey]

Playground example: https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=1ef166f9e2b31f3f4093728719de4efc

pub trait Test {
    type Ref<'a> where Test: 'a;
}

impl<T, U> Test for (T,) {
    type Ref<'a> = (&'a T,) where T: 'a;
}

impl<T, U> Test for (T, U) {
    type Ref<'a> = (&'a T, &'a U) where T: 'a, U: 'a;
}

The above autoformats to:

pub trait Test {
    type Ref<'a>
    where
        Test: 'a;
}

impl<T, U> Test for (T,) {
    type Ref<'a> = (&'a T,) where T: 'a;
}

impl<T, U> Test for (T, U) {
    type Ref<'a> = (&'a T, &'a U) where T: 'a, U: 'a;
}

You'll notice that the where clauses for the impls aren't formatted at all, whereas I would expect:

pub trait Test {
    type Ref<'a>
    where
        Test: 'a;
}

impl<T, U> Test for (T,) {
    type Ref<'a> = (&'a T,)
    where
        T: 'a;
}

impl<T, U> Test for (T, U) {
    type Ref<'a> = (&'a T, &'a U)
    where
        T: 'a,
        U: 'a;
}

[ytmimi]

Thanks for reaching out!

I haven't had a chance to look into this yet, but I'll try to dig into this when I've got a little more time

[richard-uk1]

I hit an issue where a longer GAT where clause had a linebreak inserted. This then caused an internal error on rustfmt --check. I suspect this issue will go away as and when formatting for GATs is implemented, but wanted to record it.

[ytmimi]

@derekdreery would it be possible for you to post a code snippet? It would help in the investigation!

[richard-uk1]

Hi @ytmimi. It seems like I can't reproduce the problem - good news! It might have been something to do with the upgrade that is now resolved. Will report back here if I manage to reproduce it again.

[ytmimi]

That is good news! I appreciate you taking the time to look into it

[richard-uk1]

@ytmimi no worries thanks for an awesome tool!

[CJKay]

Still seems to be occurring - the associated type declaration in the trait formats fine, but the impl remains untouched. This is very simple to reproduce: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=9bd99971b4d896d785caed1506993ee4

[tamird]

Note that this doesn't require GATs; it happens on any associated type in an impl that has a where clause. From #5751: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=448e25cc22bb316f236e5ee6aeb455de.

[clarfonthey]

Aren't those still considered GATs? I was under the impression that any conditions on associated types were forbidden before GATs were stabilised, and the code is shared for all of them.

[ia0]

I suspect this is now fixed, although in a weird way. Notice how the actual output differs from the expected output in the original issue comment. You can use the playground link provided there to reproduce.

pub trait Test {
    type Ref<'a>
    where
        Test: 'a;
}

impl<T, U> Test for (T,) {
    type Ref<'a>
        = (&'a T,)
    where
        T: 'a;
}

impl<T, U> Test for (T, U) {
    type Ref<'a>
        = (&'a T, &'a U)
    where
        T: 'a,
        U: 'a;
}