From b7ff1684f3ac2c1b74d9a95510bc54121eb3e6a0 Mon Sep 17 00:00:00 2001
From: John Vandenberg <jayvdb@gmail.com>
Date: Fri, 6 May 2016 22:18:15 +0700
Subject: [PATCH] Manage recursion limit preventing RuntimeError

pyflakes has traditionally recursed with a handler for every
level of the ast.  The ast depth can become very large, especially
for an expression containing many binary operators.

Python has a maximum recursion limit, defaulting to a low number
like 1000, which resulted in a RuntimeError for the ast of:

    x = 1 + 2 + 3 + ... + 1001

To workaround this problem, pyflakes now increases the recursion
limit at runtime when it knows it will be exceeded.

Fixes lp:1507827
---
 pyflakes/checker.py         |  7 +++++++
 pyflakes/test/test_other.py | 16 ++++++++++++++++
 2 files changed, 23 insertions(+)

diff --git a/pyflakes/checker.py b/pyflakes/checker.py
index 9545cab9..49029b4c 100644
--- a/pyflakes/checker.py
+++ b/pyflakes/checker.py
@@ -734,6 +734,13 @@ def on_conditional_branch():
                 self.report(messages.UndefinedName, node, name)
 
     def handleChildren(self, tree, omit=None):
+        # The recursion limit needs to be at least double nodeDepth
+        # as the recursion cycles between handleChildren and handleNode.
+        # Set it to triple nodeDepth to account for other items on the stack,
+        # and to reduce the frequency of changes to the limit.
+        acceptable_recursion_limit = self.nodeDepth * 3
+        if sys.getrecursionlimit() <= acceptable_recursion_limit:
+            sys.setrecursionlimit(acceptable_recursion_limit)
         for node in iter_child_nodes(tree, omit=omit):
             self.handleNode(node, tree)
 
diff --git a/pyflakes/test/test_other.py b/pyflakes/test/test_other.py
index ae6cea24..531f063d 100644
--- a/pyflakes/test/test_other.py
+++ b/pyflakes/test/test_other.py
@@ -1,6 +1,7 @@
 """
 Tests for various Pyflakes behavior.
 """
+import sys
 
 from sys import version_info
 
@@ -1743,3 +1744,18 @@ def test_matmul(self):
         def foo(a, b):
             return a @ b
         ''')
+
+
+class TestMaximumRecursion(TestCase):
+
+    def setUp(self):
+        self._recursionlimit = sys.getrecursionlimit()
+
+    def test_recursion_limit(self):
+        # Using self._recursionlimit * 10 tends to cause CPython to core dump.
+        r = range(self._recursionlimit * 9)
+        s = 'x = ' + ' + '.join(str(n) for n in r)
+        self.flakes(s)
+
+    def tearDown(self):
+        sys.setrecursionlimit(self._recursionlimit)