[parser] Supports root node.

Author: springcomp

jmespath/ast.py

@@ -10,6 +10,10 @@ def current_node():
     return {'type': 'current', 'children': []}
 
 
+def root_node():
+    return {'type': 'root', 'children': []}
+
+
 def expref(expression):
     return {'type': 'expref', 'children': [expression]}
 

jmespath/parser.py

@@ -46,6 +46,7 @@ class Parser(object):
         'rbrace': 0,
         'number': 0,
         'current': 0,
+        'root': 0,
         'expref': 0,
         'colon': 0,
         'pipe': 1,
@@ -239,6 +240,9 @@ def _parse_slice_expression(self):
     def _token_nud_current(self, token):
         return ast.current_node()
 
+    def _token_nud_root(self, token):
+        return ast.root_node()
+
     def _token_nud_expref(self, token):
         expression = self._expression(self.BINDING_POWER['expref'])
         return ast.expref(expression)

tests/test_parser.py

@@ -106,6 +106,17 @@ def test_function_call_with_and_statement(self):
              'type': 'function_expression',
              'value': 'f'})
 
+    def test_root_node(self):
+        self.assert_parsed_ast(
+            '$[0]',
+            {
+                'type': 'index_expression',
+                'children': [
+                    {'type': 'root', 'children': []},
+                    {'type': 'index', 'value': 0, 'children': []}
+                ]
+            })
+
 
 class TestErrorMessages(unittest.TestCase):