Fix internal error when trying to detect the start of a recursive tra…

…ceback.

Fix pytest-dev#2486

_pytest/_code/code.py

@@ -640,8 +640,11 @@ def _truncate_recursive_traceback(self, traceback):
             ).format(exc_type=type(e).__name__, exc_msg=safe_str(e), max_frames=max_frames, total=len(traceback))
             traceback = traceback[:max_frames] + traceback[-max_frames:]
         else:
-            extraline = "!!! Recursion detected (same locals & position)"
-            traceback = traceback[:recursionindex + 1]
+            if recursionindex is not None:
+                extraline = "!!! Recursion detected (same locals & position)"
+                traceback = traceback[:recursionindex + 1]
+            else:
+                extraline = None
 
         return traceback, extraline
 

changelog/2486.bugfix

@@ -0,0 +1 @@
+Fix internal error when trying to detect the start of a recursive traceback.

testing/code/test_excinfo.py

@@ -1173,3 +1173,21 @@ def b(x):
             '*The following exception happened*',
             '*ValueError: The truth value of an array*',
         ])
+
+
+def test_no_recursion_index_on_recursion_error():
+    """
+    Ensure that we don't break in case we can't find the recursion index
+    during a recursion error (#2486).
+    """
+    try:
+        class RecursionDepthError(object):
+            def __getattr__(self, attr):
+                return getattr(self, '_' + attr)
+
+        RecursionDepthError().trigger
+        assert 0
+    except:
+        from _pytest._code.code import ExceptionInfo
+        exc_info = ExceptionInfo()
+        assert 'maximum recursion' in str(exc_info.getrepr())