Typecheck tags in "alt" patterns

src/boot/me/type.ml

@@ -903,8 +903,10 @@ let check_stmt (cx:Semant.ctxt) : (fn_ctx -> Ast.stmt -> unit) =
           let arg_tys =
             match constr_ty with
                 Ast.TY_fn (ty_sig, _) ->
+                  demand expected (get_slot_ty ty_sig.Ast.sig_output_slot);
                   Array.map get_slot_ty ty_sig.Ast.sig_input_slots
               | Ast.TY_tag _ ->
+                  demand expected constr_ty;
                   [||]
               | _ -> type_error "constructor function" constr_ty
           in

src/test/compile-fail/alt-tag-nullary.rs

@@ -0,0 +1,12 @@
+// error-pattern: mismatched types
+
+tag a { A; }
+tag b { B; }
+
+fn main() {
+    let a x = A;
+    alt (x) {
+        case (B) {}
+    }
+}
+

src/test/compile-fail/alt-tag-unary.rs

@@ -0,0 +1,12 @@
+// error-pattern: mismatched types
+
+tag a { A(int); }
+tag b { B(int); }
+
+fn main() {
+    let a x = A(0);
+    alt (x) {
+        case (B(?y)) {}
+    }
+}
+