From 8f028ebf6813512ec59b89a7f8c03eadd1bae9e5 Mon Sep 17 00:00:00 2001
From: Max Brunsfeld <maxbrunsfeld@gmail.com>
Date: Wed, 5 Jul 2017 17:33:35 -0700
Subject: [PATCH] Avoid deep tree comparison when both trees have errors

---
 src/runtime/parser.c                             | 2 ++
 test/fixtures/error_corpus/javascript_errors.txt | 2 +-
 test/runtime/parser_test.cc                      | 3 ++-
 3 files changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/runtime/parser.c b/src/runtime/parser.c
index 5e2f75f3..13ef9a76 100644
--- a/src/runtime/parser.c
+++ b/src/runtime/parser.c
@@ -452,6 +452,8 @@ static bool parser__select_tree(Parser *self, Tree *left, Tree *right) {
     return false;
   }
 
+  if (left->error_cost > 0) return -1;
+
   int comparison = ts_tree_compare(left, right);
   switch (comparison) {
     case -1:
diff --git a/test/fixtures/error_corpus/javascript_errors.txt b/test/fixtures/error_corpus/javascript_errors.txt
index 02edfb48..f4f99bc8 100644
--- a/test/fixtures/error_corpus/javascript_errors.txt
+++ b/test/fixtures/error_corpus/javascript_errors.txt
@@ -53,8 +53,8 @@ if ({a: 'b'} {c: 'd'}) {
 
 (program
   (if_statement
+    (ERROR (object (pair (identifier) (string))))
     (object (pair (identifier) (string)))
-    (ERROR (statement_block (labeled_statement (identifier) (expression_statement (string)))))
     (statement_block
       (expression_statement (assignment
         (identifier)
diff --git a/test/runtime/parser_test.cc b/test/runtime/parser_test.cc
index 0c7e30a3..f680ecf5 100644
--- a/test/runtime/parser_test.cc
+++ b/test/runtime/parser_test.cc
@@ -398,7 +398,8 @@ describe("Parser", [&]() {
 
         assert_root_node(
           "(program "
-            "(expression_statement (number) (ERROR (number))) "
+            "(ERROR (number)) "
+            "(expression_statement (number)) "
             "(expression_statement (math_op (number) (number))))");
       });
     });