1 files changed, 34 insertions, 0 deletions
diff --git a/compiler/rustc_trait_selection/src/solve/project_goals/weak_types.rs b/compiler/rustc_trait_selection/src/solve/project_goals/weak_types.rs
new file mode 100644
index 000000000..54de32cf6
--- /dev/null
+++ b/compiler/rustc_trait_selection/src/solve/project_goals/weak_types.rs
@@ -0,0 +1,34 @@
+//! Computes a normalizes-to (projection) goal for inherent associated types,
+//! `#![feature(lazy_type_alias)]` and `#![feature(type_alias_impl_trait)]`.
+//!
+//! Since a weak alias is not ambiguous, this just computes the `type_of` of
+//! the alias and registers the where-clauses of the type alias.
+use rustc_middle::traits::solve::{Certainty, Goal, QueryResult};
+use rustc_middle::ty;
+
+use super::EvalCtxt;
+
+impl<'tcx> EvalCtxt<'_, 'tcx> {
+    pub(super) fn normalize_weak_type(
+        &mut self,
+        goal: Goal<'tcx, ty::ProjectionPredicate<'tcx>>,
+    ) -> QueryResult<'tcx> {
+        let tcx = self.tcx();
+        let weak_ty = goal.predicate.projection_ty;
+        let expected = goal.predicate.term.ty().expect("no such thing as a const alias");
+
+        let actual = tcx.type_of(weak_ty.def_id).instantiate(tcx, weak_ty.args);
+        self.eq(goal.param_env, expected, actual)?;
+
+        // Check where clauses
+        self.add_goals(
+            tcx.predicates_of(weak_ty.def_id)
+                .instantiate(tcx, weak_ty.args)
+                .predicates
+                .into_iter()
+                .map(|pred| goal.with(tcx, pred)),
+        );
+
+        self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
+    }
+}