ui: flush stderr after printing a non-chained exception for Windows There were consistent test failures in test-bad-extension.t, because Windows buffers stderr when redirected to a file (per the comment in ui.write_err()). That resulted in failures like this: --- c:/Users/Matt/Projects/hg/tests/test-bad-extension.t +++ c:/Users/Matt/Projects/hg/tests/test-bad-extension.t.err @@ -23,11 +23,11 @@ Traceback (most recent call last): Exception: bit bucket overflow *** failed to import extension badext2: No module named badext2 - Traceback (most recent call last): - ImportError: No module named badext2 hg help [-ec] [TOPIC] show help for a given topic or a help overview + Traceback (most recent call last): + ImportError: No module named badext2 show traceback for ImportError of hgext.name if debug is set (note that --debug option isn't applied yet when loading extensions) Instead of inserting another flush immediately after the print, to go along with the one recently added prior to the print (see 3ff4b07412ad), funnel the output through ui.write_err(). The flush prior to printing the traceback only mentions that stdout needs to be flushed, and only stderr needs to be flushed after printing the traceback. ui.write_err() does both for us without needing to redocument the quirky Windows behavior. It will also clear any progress bar.

--- a/mercurial/ui.py	Thu Jun 11 19:02:24 2015 -0700
+++ b/mercurial/ui.py	Fri Jun 12 22:09:41 2015 -0400
@@ -869,9 +869,8 @@
                                ''.join(causetb),
                                ''.join(exconly))
             else:
-                self.flush()  # flush debug or status message
-                traceback.print_exception(exc[0], exc[1], exc[2],
-                                          file=self.ferr)
+                output = traceback.format_exception(exc[0], exc[1], exc[2])
+                self.write_err(''.join(output))
         return self.tracebackflag or force
 
     def geteditor(self):