--- a/mercurial/scmutil.py	Thu Dec 14 21:30:00 2017 +0800
+++ b/mercurial/scmutil.py	Sun Oct 01 12:21:50 2017 +0100
@@ -1100,12 +1100,11 @@
     finally:
         if proc:
             proc.communicate()
-            if proc.returncode != 0:
-                # not an error so 'cmd | grep' can be empty
-                repo.ui.debug("extdata command '%s' %s\n"
-                              % (cmd, util.explainexit(proc.returncode)[0]))
         if src:
             src.close()
+    if proc and proc.returncode != 0:
+        raise error.Abort(_("extdata command '%s' failed: %s")
+                          % (cmd, util.explainexit(proc.returncode)[0]))
 
     return data