don't convert str to tuple in TupleParameter (#3275)

* fix: don't convert str to tuple in TupleParameter

* fix: don't compare message in other library.

jsonschema validation error message was changed. I think it is very flaky test.

luigi/parameter.py

@@ -1379,10 +1379,15 @@ def parse(self, x):
         # ast.literal_eval(t_str) == t
         try:
             # loop required to parse tuple of tuples
-            return tuple(tuple(x) for x in json.loads(x, object_pairs_hook=FrozenOrderedDict))
+            return tuple(self._convert_iterable_to_tuple(x) for x in json.loads(x, object_pairs_hook=FrozenOrderedDict))
         except (ValueError, TypeError):
             return tuple(literal_eval(x))  # if this causes an error, let that error be raised.
 
+    def _convert_iterable_to_tuple(self, x):
+        if isinstance(x, str):
+            return x
+        return tuple(x)
+
 
 class OptionalTupleParameter(OptionalParameterMixin, TupleParameter):
     """Class to parse optional tuple parameters."""

test/list_parameter_test.py

@@ -81,7 +81,7 @@ def test_schema(self):
             a.normalize(["INVALID_ATTRIBUTE"])
 
         # Check that empty list is not valid
-        with pytest.raises(ValidationError, match=r"\[\] is too short"):
+        with pytest.raises(ValidationError):
             a.normalize([])
 
         # Check that valid lists work

test/parameter_test.py

@@ -533,6 +533,14 @@ class Foo(luigi.Task):
         self.assertEqual(hash(Foo(args=(('foo', 'bar'), ('doge', 'wow'))).args),
                          hash(p.normalize(p.parse('(("foo", "bar"), ("doge", "wow"))'))))
 
+    def test_tuple_string_with_json(self):
+        class Foo(luigi.Task):
+            args = luigi.parameter.TupleParameter()
+
+        p = luigi.parameter.TupleParameter()
+        self.assertEqual(hash(Foo(args=('foo', 'bar')).args),
+                         hash(p.normalize(p.parse('["foo", "bar"]'))))
+
     def test_task(self):
         class Bar(luigi.Task):
             pass