Disable ForestToParseTree cache when ambiguity='resolve'

lark/parsers/earley.py

@@ -300,7 +300,10 @@ def parse(self, lexer, start):
 
         if self.Tree is not None:
             # Perform our SPPF -> AST conversion
-            transformer = ForestToParseTree(self.Tree, self.callbacks, self.forest_sum_visitor and self.forest_sum_visitor(), self.resolve_ambiguity)
+            # Disable the ForestToParseTree cache when ambiguity='resolve'
+            # to prevent a tree construction bug. See issue #1283
+            use_cache = not self.resolve_ambiguity
+            transformer = ForestToParseTree(self.Tree, self.callbacks, self.forest_sum_visitor and self.forest_sum_visitor(), self.resolve_ambiguity, use_cache)
             solutions = [transformer.transform(s) for s in solutions]
 
             if len(solutions) > 1:

lark/parsers/earley_forest.py

@@ -609,9 +609,10 @@ def transform_packed_node(self, node, data):
                 children.append(data.left)
         if data.right is not PackedData.NO_DATA:
             children.append(data.right)
-        if node.parent.is_intermediate:
-            return self._cache.setdefault(id(node), children)
-        return self._cache.setdefault(id(node), self._call_rule_func(node, children))
+        transformed = children if node.parent.is_intermediate else self._call_rule_func(node, children)
+        if self._use_cache:
+            self._cache[id(node)] = transformed
+        return transformed
 
     def visit_symbol_node_in(self, node):
         super(ForestToParseTree, self).visit_symbol_node_in(node)

tests/test_parser.py

@@ -954,6 +954,26 @@ def test_symbol_node_start_end_dynamic_lexer(self):
             self.assertEqual(node.start, 0)
             self.assertEqual(node.end, 3)
 
+        def test_resolve_ambiguity_with_shared_node(self):
+            grammar = """
+            start: (a+)*
+            !a.1: "A" |
+            """
+
+            l = Lark(grammar, ambiguity='resolve', lexer=LEXER)
+            tree = l.parse("A")
+            self.assertEqual(tree, Tree('start', [Tree('a', []), Tree('a', []), Tree('a', ['A'])]))
+
+        def test_resolve_ambiguity_with_shared_node2(self):
+            grammar = """
+            start: _s x _s
+            x: "X"?
+            _s: " "?
+            """
+
+            l = Lark(grammar, ambiguity='resolve', lexer=LEXER)
+            tree = l.parse("")
+            self.assertEqual(tree, Tree('start', [Tree('x', [])]))
 
     _NAME = "TestFullEarley" + LEXER.capitalize()
     _TestFullEarley.__name__ = _NAME