fix(compiler): Correct error message for unbound type variables (#1327)

Author: ospencer

compiler/src/typed/typetexp.re

@@ -457,7 +457,13 @@ let globalize_used_variables = (env, fixed) => {
         try(r := [(loc, v, Tbl.find(name, type_variables^)), ...r^]) {
         | Not_found =>
           if (fixed && Btype.is_Tvar(repr(ty))) {
-            raise(Error(loc, env, Unbound_type_variable("'" ++ name)));
+            raise(
+              Error(
+                loc,
+                env,
+                Unbound_type_variable(Printf.sprintf("'%s'", name)),
+              ),
+            );
           };
           let v2 = new_global_var();
           r := [(loc, v, v2), ...r^];

compiler/test/suites/types.re

@@ -110,6 +110,13 @@ describe("aliased types", ({test, testSkip}) => {
     |},
     "Type String is not compatible with type Number",
   );
+  assertCompileError(
+    "err_type_alias_5",
+    {|
+      type Foo = List<a>
+    |},
+    "Unbound type parameter 'a'",
+  );
   assertRun(
     "import_type_alias_1",
     {|