Ignore type bindings in generic_predicates_for_param

This allows us to handle more cases without a query cycle, which
includes certain cases that rustc accepted. That in turn means we avoid
triggering salsa-rs/salsa#257 on valid code (it will still happen if the
user writes an actual cycle).

We actually accept more definitions than rustc now; that's because rustc
only ignores bindings when looking up super traits, whereas we now also
ignore them when looking for predicates to disambiguate associated type
shorthand. We could introduce a separate query for super traits if
necessary, but for now I think this should be fine.

1 files changed, 2 insertions, 3 deletions

diff --git a/crates/hir_ty/src/tests/traits.rs b/crates/hir_ty/src/tests/traits.rs
index 1bb6dff95..37cd04c6f 100644
--- a/crates/hir_ty/src/tests/traits.rs
+++ b/crates/hir_ty/src/tests/traits.rs
@@ -2273,8 +2273,7 @@ fn test<T, U>() where T: Trait<U::Item>, U: Trait<T::Item> {
 
 #[test]
 fn unselected_projection_in_trait_env_cycle_3() {
-    // this is a cycle, although it would be possible to handle if we didn't go
-    // into bindings when looking for traits
+    // this is a cycle for rustc; we currently accept it
     check_types(
         r#"
 //- /main.rs
@@ -2285,7 +2284,7 @@ trait Trait {
 
 fn test<T>() where T: Trait<OtherItem = T::Item> {
     let x: T::Item = no_matter;
-}                   //^ {unknown}
+}                   //^ Trait::Item<T>
 "#,
     );
 }