1 files changed, 53 insertions, 0 deletions

diff --git a/crates/hir_ty/src/chalk_cast.rs b/crates/hir_ty/src/chalk_cast.rs
new file mode 100644
index 000000000..bf884ae15
--- /dev/null
+++ b/crates/hir_ty/src/chalk_cast.rs
@@ -0,0 +1,53 @@
+//! Implementations of the Chalk `Cast` trait for our types.
+
+use chalk_ir::{
+    cast::{Cast, CastTo},
+    interner::HasInterner,
+};
+
+use crate::{AliasEq, DomainGoal, Interner, TraitRef, WhereClause};
+
+macro_rules! has_interner {
+    ($t:ty) => {
+        impl HasInterner for $t {
+            type Interner = crate::Interner;
+        }
+    };
+}
+
+has_interner!(WhereClause);
+has_interner!(DomainGoal);
+
+impl CastTo<WhereClause> for TraitRef {
+    fn cast_to(self, _interner: &Interner) -> WhereClause {
+        WhereClause::Implemented(self)
+    }
+}
+
+impl CastTo<WhereClause> for AliasEq {
+    fn cast_to(self, _interner: &Interner) -> WhereClause {
+        WhereClause::AliasEq(self)
+    }
+}
+
+impl CastTo<DomainGoal> for WhereClause {
+    fn cast_to(self, _interner: &Interner) -> DomainGoal {
+        DomainGoal::Holds(self)
+    }
+}
+
+macro_rules! transitive_impl {
+    ($a:ty, $b:ty, $c:ty) => {
+        impl CastTo<$c> for $a {
+            fn cast_to(self, interner: &Interner) -> $c {
+                self.cast::<$b>(interner).cast(interner)
+            }
+        }
+    };
+}
+
+// In Chalk, these can be done as blanket impls, but that doesn't work here
+// because of coherence
+
+transitive_impl!(TraitRef, WhereClause, DomainGoal);
+transitive_impl!(AliasEq, WhereClause, DomainGoal);