An associated type is not a projection!
More correctly, a `TyKind::AssociatedType` is not the same as `TyKind::Projection`.
We used to map next-solver `TyKind::Alias` to Chalk's `TyKind::AssociatedType`. This is very incorrect, as `AssociatedType` is assumed to be fully normalized, and caused a lot of type mismatches.
Unfortunately fixing this causes a lot of stack overflows, because the next solver doesn't have something akin to `AssociatedType` so we normalize again and again. The reason is that is the lazy-normalization nature of the next solver, which means we need to stop normalizing everything. This will be fixed in the next commit.
diff --git a/crates/hir-ty/src/next_solver/mapping.rs b/crates/hir-ty/src/next_solver/mapping.rs
index f66b8da..57a56b3 100644
--- a/crates/hir-ty/src/next_solver/mapping.rs
+++ b/crates/hir-ty/src/next_solver/mapping.rs
@@ -1358,7 +1358,10 @@
};
let associated_ty_id = to_assoc_type_id(assoc_ty_id);
let substitution = convert_args_for_result(interner, alias_ty.args.as_slice());
- TyKind::AssociatedType(associated_ty_id, substitution)
+ TyKind::Alias(crate::AliasTy::Projection(crate::ProjectionTy {
+ associated_ty_id,
+ substitution,
+ }))
}
rustc_type_ir::AliasTyKind::Opaque => {
let opaque_ty_id = match alias_ty.def_id {
diff --git a/crates/hir-ty/src/tests/regression/new_solver.rs b/crates/hir-ty/src/tests/regression/new_solver.rs
index 97473bb..471108d 100644
--- a/crates/hir-ty/src/tests/regression/new_solver.rs
+++ b/crates/hir-ty/src/tests/regression/new_solver.rs
@@ -71,3 +71,30 @@
}"#,
);
}
+
+#[test]
+fn projection_is_not_associated_type() {
+ check_no_mismatches(
+ r#"
+//- minicore: fn
+trait Iterator {
+ type Item;
+
+ fn partition<F>(self, f: F)
+ where
+ F: FnMut(&Self::Item) -> bool,
+ {
+ }
+}
+
+struct Iter;
+impl Iterator for Iter {
+ type Item = i32;
+}
+
+fn main() {
+ Iter.partition(|n| true);
+}
+ "#,
+ );
+}
