3 files changed, 18 insertions, 2 deletions

diff --git a/crates/hir_ty/src/db.rs b/crates/hir_ty/src/db.rs
index 25cf9eb7f..57e60c53b 100644
--- a/crates/hir_ty/src/db.rs
+++ b/crates/hir_ty/src/db.rs
@@ -26,6 +26,9 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
     #[salsa::invoke(crate::infer::infer_query)]
     fn infer_query(&self, def: DefWithBodyId) -> Arc<InferenceResult>;
 
+    #[salsa::invoke(crate::infer::can_unify)]
+    fn can_unify(&self, def: DefWithBodyId, ty1: Ty, ty2: Ty) -> bool;
+
     #[salsa::invoke(crate::lower::ty_query)]
     #[salsa::cycle(crate::lower::ty_recover)]
     fn ty(&self, def: TyDefId) -> Binders<Ty>;
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 03b00b101..d461e077b 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -55,7 +55,7 @@ macro_rules! ty_app {
     };
 }
 
-mod unify;
+pub mod unify;
 mod path;
 mod expr;
 mod pat;
@@ -78,6 +78,19 @@ pub(crate) fn infer_query(db: &dyn HirDatabase, def: DefWithBodyId) -> Arc<Infer
     Arc::new(ctx.resolve_all())
 }
 
+pub(crate) fn can_unify(db: &dyn HirDatabase, def: DefWithBodyId, ty1: Ty, ty2: Ty) -> bool {
+    let resolver = def.resolver(db.upcast());
+    let mut ctx = InferenceContext::new(db, def, resolver);
+
+    let ty1 = ctx.canonicalizer().canonicalize_ty(ty1).value;
+    let ty2 = ctx.canonicalizer().canonicalize_ty(ty2).value;
+    let mut kinds = Vec::from(ty1.kinds.to_vec());
+    kinds.extend_from_slice(ty2.kinds.as_ref());
+    let tys = crate::Canonical::new((ty1.value, ty2.value), kinds);
+
+    unify(&tys).is_some()
+}
+
 #[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
 enum ExprOrPatId {
     ExprId(ExprId),
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index 1e748476a..681f98bde 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -43,7 +43,7 @@ use crate::{
 };
 
 pub use autoderef::autoderef;
-pub use infer::{InferTy, InferenceResult};
+pub use infer::{unify, InferTy, InferenceResult};
 pub use lower::CallableDefId;
 pub use lower::{
     associated_type_shorthand_candidates, callable_item_sig, ImplTraitLoweringMode, TyDefId,