diff -r 2a42ca2679e2 -r 1cb54e6193a6 mercurial/pycompat.py
--- a/mercurial/pycompat.py	Sat Apr 14 02:06:03 2018 +0530
+++ b/mercurial/pycompat.py	Fri Apr 13 18:17:45 2018 -0400
@@ -28,6 +28,9 @@
     import xmlrpclib
 
     from .thirdparty.concurrent import futures
+
+    def future_set_exception_info(f, exc_info):
+        f.set_exception_info(*exc_info)
 else:
     import concurrent.futures as futures
     import http.cookiejar as cookielib
@@ -37,6 +40,9 @@
     import socketserver
     import xmlrpc.client as xmlrpclib
 
+    def future_set_exception_info(f, exc_info):
+        f.set_exception(exc_info[0])
+
 empty = _queue.Empty
 queue = _queue.Queue