Make let statements kind of work

crates/ra_syntax/src/ast/generated.rs

@@ -1561,6 +1561,10 @@ impl<'a> LetStmt<'a> {
         super::child_opt(self)
     }
 
+    pub fn type_ref(self) -> Option<TypeRef<'a>> {
+        super::child_opt(self)
+    }
+
     pub fn initializer(self) -> Option<Expr<'a>> {
         super::child_opt(self)
     }

crates/ra_syntax/src/grammar.ron

@@ -499,6 +499,7 @@ Grammar(
         ),
         "LetStmt": ( options: [
             ["pat", "Pat"],
+            ["type_ref", "TypeRef"],
             ["initializer", "Expr"],
         ]),
         "Condition": (