e568cb45fe
Make the GATS self outlives error take into GATs in the inputs
Before, the reasoning was that outlives should factor in to the outlives error, because that value is produced and inputs aren't. However, this is potentially confusing, and we can just require this for now and relax it later if we need. GATs in where clauses still don't count for the self outlives error, and I've added a test for that.
This now errors:
```rust
trait Input {
type Item<'a>;
//~^ missing required
fn takes_item<'a>(&'a self, item: Self::Item<'a>);
}
```
I've also added a test that this does not:
```rust
trait WhereClause {
type Item<'a>;
fn takes_item<'a>(&'a self) where Self::Item<'a>: ;
}
```
r? ``@compiler-errors``
For high-level intro to how type checking works in rustc, see the type checking chapter of the rustc dev guide.