bpo-29854: Add failing test that crash readline

readline segfaults on input() if the number of items in the history file
is equal or more to history size * 2.

This issue affects only GNU readline. When using libedit emulation
system history size option does not work.

Author: nirs

Lib/test/test_readline.py

@@ -9,7 +9,7 @@
 import sys
 import tempfile
 import unittest
-from test.support import import_module, unlink, TESTFN
+from test.support import import_module, unlink, temp_dir, TESTFN
 from test.support.script_helper import assert_python_ok
 
 # Skip tests if there is no readline module
@@ -210,6 +210,44 @@ def display(substitution, matches, longest_match_length):
         self.assertIn(b"result " + expected + b"\r\n", output)
         self.assertIn(b"history " + expected + b"\r\n", output)
 
+    @unittest.skipIf(is_editline,
+                     "editline history size configuration is broken")
+    @unittest.expectedFailure
+    def test_history_size(self):
+        history_size = 10
+        with temp_dir() as test_dir:
+            inputrc = os.path.join(test_dir, "inputrc")
+            with open(inputrc, "wb") as f:
+                f.write(b"set history-size %d\n" % history_size)
+
+            history_file = os.path.join(test_dir, "history")
+            with open(history_file, "wb") as f:
+                # history_size * 2 items crashes readline
+                data = b"".join(b"item %d\n" % i
+                                for i in range(history_size * 2))
+                f.write(data)
+
+            script = """
+import os
+import readline
+
+history_file = os.environ["HISTORY_FILE"]
+readline.read_history_file(history_file)
+input()
+readline.write_history_file(history_file)
+"""
+
+            env = dict(os.environ)
+            env["INPUTRC"] = inputrc
+            env["HISTORY_FILE"] = history_file
+
+            run_pty(script, input=b"last input\r", env=env)
+
+            with open(history_file, "rb") as f:
+                lines = f.readlines()
+            self.assertEqual(len(lines), history_size)
+            self.assertEqual(lines[-1].strip(), b"last input")
+
 
 def run_pty(script, input=b"dummy input\r", env=None):
     pty = import_module('pty')