--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/tests/logexceptions.py	Mon Nov 20 23:02:32 2017 -0800
@@ -0,0 +1,73 @@
+# logexceptions.py - Write files containing info about Mercurial exceptions
+#
+# Copyright 2017 Matt Mackall <mpm@selenic.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+
+import inspect
+import os
+import sys
+import traceback
+import uuid
+
+from mercurial import (
+    dispatch,
+    extensions,
+)
+
+def handleexception(orig, ui):
+    res = orig(ui)
+
+    if not ui.environ.get(b'HGEXCEPTIONSDIR'):
+        return res
+
+    dest = os.path.join(ui.environ[b'HGEXCEPTIONSDIR'],
+                        str(uuid.uuid4()).encode('ascii'))
+
+    exc_type, exc_value, exc_tb = sys.exc_info()
+
+    stack = []
+    tb = exc_tb
+    while tb:
+        stack.append(tb)
+        tb = tb.tb_next
+    stack.reverse()
+
+    hgframe = 'unknown'
+    hgline = 'unknown'
+
+    # Find the first Mercurial frame in the stack.
+    for tb in stack:
+        mod = inspect.getmodule(tb)
+        if not mod.__name__.startswith(('hg', 'mercurial')):
+            continue
+
+        frame = tb.tb_frame
+
+        try:
+            with open(inspect.getsourcefile(tb), 'r') as fh:
+                hgline = fh.readlines()[frame.f_lineno - 1].strip()
+        except (IndexError, OSError):
+            pass
+
+        hgframe = '%s:%d' % (frame.f_code.co_filename, frame.f_lineno)
+        break
+
+    primary = traceback.extract_tb(exc_tb)[-1]
+    primaryframe = '%s:%d' % (primary.filename, primary.lineno)
+
+    with open(dest, 'wb') as fh:
+        parts = [
+            str(exc_value),
+            primaryframe,
+            hgframe,
+            hgline,
+        ]
+        fh.write(b'\0'.join(p.encode('utf-8', 'replace') for p in parts))
+
+def extsetup(ui):
+    extensions.wrapfunction(dispatch, 'handlecommandexception',
+                            handleexception)