fix: deep-copy literal values so changes do not propagate across calls

jmespath/visitor.py

@@ -1,3 +1,4 @@
+import copy
 import operator
 
 from jmespath import functions
@@ -225,7 +226,7 @@ def visit_key_val_pair(self, node, value):
         return self.visit(node['children'][0], value)
 
     def visit_literal(self, node, value):
-        return node['value']
+        return copy.deepcopy(node['value'])
 
     def visit_multi_select_dict(self, node, value):
         if value is None:

tests/test_search.py

@@ -62,3 +62,33 @@ def test_can_handle_decimals_as_numeric_type(self):
         result = decimal.Decimal('3')
         self.assertEqual(jmespath.search('[?a >= `1`].a', [{'a': result}]),
                          [result])
+
+    def test_literal_empty_list_changes_do_not_propagate(self):
+        first = jmespath.search('`[]`', {})
+        first.extend([1, 2, 3])
+        second = jmespath.search('`[]`', {})
+        self.assertEqual(second, [])
+
+    def test_literal_list_changes_do_not_propagate(self):
+        first = jmespath.search('`[1, 2, 3]`', {})
+        first.append(99)
+        second = jmespath.search('`[1, 2, 3]`', {})
+        self.assertEqual(second, [1, 2, 3])
+
+    def test_literal_nested_dict_changes_do_not_propagate(self):
+        first = jmespath.search('`{"key": [1, 2, 3]}`', {})
+        first['key'].append(99)
+        second = jmespath.search('`{"key": [1, 2, 3]}`', {})
+        self.assertEqual(second, {'key': [1, 2, 3]})
+
+    def test_literal_dict_added_key_does_not_propagate(self):
+        first = jmespath.search('`{"a": 1}`', {})
+        first['new_key'] = 99
+        second = jmespath.search('`{"a": 1}`', {})
+        self.assertEqual(second, {'a': 1})
+
+    def test_literal_dict_overwritten_key_does_not_propagate(self):
+        first = jmespath.search('`{"a": 1}`', {})
+        first['a'] = 99
+        second = jmespath.search('`{"a": 1}`', {})
+        self.assertEqual(second, {'a': 1})