Add cycle recovery for type aliases

Author: flodiebold

crates/ra_hir_ty/src/db.rs

@@ -22,6 +22,7 @@ pub trait HirDatabase: DefDatabase {
     fn infer(&self, def: DefWithBodyId) -> Arc<InferenceResult>;
 
     #[salsa::invoke(crate::lower::ty_query)]
+    #[salsa::cycle(crate::lower::ty_recover)]
     fn ty(&self, def: TyDefId) -> Ty;
 
     #[salsa::invoke(crate::lower::value_ty_query)]

crates/ra_hir_ty/src/lower.rs

@@ -742,6 +742,11 @@ pub(crate) fn ty_query(db: &impl HirDatabase, def: TyDefId) -> Ty {
         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
     }
 }
+
+pub(crate) fn ty_recover(_db: &impl HirDatabase, _cycle: &[String], _def: &TyDefId) -> Ty {
+    Ty::Unknown
+}
+
 pub(crate) fn value_ty_query(db: &impl HirDatabase, def: ValueTyDefId) -> Ty {
     match def {
         ValueTyDefId::FunctionId(it) => type_for_fn(db, it),

crates/ra_hir_ty/src/tests.rs

@@ -2154,7 +2154,6 @@ fn test(x: Foo, y: Bar<&str>, z: Baz<i8, u8>) {
 }
 
 #[test]
-#[should_panic] // we currently can't handle this
 fn recursive_type_alias() {
     assert_snapshot!(
         infer(r#"
@@ -2163,7 +2162,10 @@ type Foo = Foo;
 type Bar = A<Bar>;
 fn test(x: Foo) {}
 "#),
-        @""
+        @r###"
+    [59; 60) 'x': {unknown}
+    [67; 69) '{}': ()
+    "###
     )
 }