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.

mercurial/ui.py

@@ -1,1017 +1,1016 b''
 # ui.py - user interface bits for mercurial
 #
 # Copyright 2005-2007 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from i18n import _
 import errno, getpass, os, socket, sys, tempfile, traceback
 import config, scmutil, util, error, formatter, progress
 from node import hex
 
 samplehgrcs = {
     'user':
 """# example user config (see "hg help config" for more info)
 [ui]
 # name and email, e.g.
 # username = Jane Doe <[e-mail]>
 username =
 
 [extensions]
 # uncomment these lines to enable some popular extensions
 # (see "hg help extensions" for more info)
 #
 # pager =
 # progress =
 # color =""",
 
     'cloned':
 """# example repository config (see "hg help config" for more info)
 [paths]
 default = %s
 
 # path aliases to other clones of this repo in URLs or filesystem paths
 # (see "hg help config.paths" for more info)
 #
 # default-push = ssh://[e-mail]/hg/jdoes-fork
 # my-fork      = ssh://[e-mail]/hg/jdoes-fork
 # my-clone     = /home/jdoe/jdoes-clone
 
 [ui]
 # name and email (local to this repository, optional), e.g.
 # username = Jane Doe <[e-mail]>
 """,
 
     'local':
 """# example repository config (see "hg help config" for more info)
 [paths]
 # path aliases to other clones of this repo in URLs or filesystem paths
 # (see "hg help config.paths" for more info)
 #
 # default      = http://example.com/hg/example-repo
 # default-push = ssh://[e-mail]/hg/jdoes-fork
 # my-fork      = ssh://[e-mail]/hg/jdoes-fork
 # my-clone     = /home/jdoe/jdoes-clone
 
 [ui]
 # name and email (local to this repository, optional), e.g.
 # username = Jane Doe <[e-mail]>
 """,
 
     'global':
 """# example system-wide hg config (see "hg help config" for more info)
 
 [extensions]
 # uncomment these lines to enable some popular extensions
 # (see "hg help extensions" for more info)
 #
 # blackbox =
 # progress =
 # color =
 # pager =""",
 }
 
 class ui(object):
     def __init__(self, src=None):
         # _buffers: used for temporary capture of output
         self._buffers = []
         # _bufferstates:
         #   should the temporary capture include stderr and subprocess output
         self._bufferstates = []
         self.quiet = self.verbose = self.debugflag = self.tracebackflag = False
         self._reportuntrusted = True
         self._ocfg = config.config() # overlay
         self._tcfg = config.config() # trusted
         self._ucfg = config.config() # untrusted
         self._trustusers = set()
         self._trustgroups = set()
         self.callhooks = True
 
         if src:
             self.fout = src.fout
             self.ferr = src.ferr
             self.fin = src.fin
 
             self._tcfg = src._tcfg.copy()
             self._ucfg = src._ucfg.copy()
             self._ocfg = src._ocfg.copy()
             self._trustusers = src._trustusers.copy()
             self._trustgroups = src._trustgroups.copy()
             self.environ = src.environ
             self.callhooks = src.callhooks
             self.fixconfig()
         else:
             self.fout = sys.stdout
             self.ferr = sys.stderr
             self.fin = sys.stdin
 
             # shared read-only environment
             self.environ = os.environ
             # we always trust global config files
             for f in scmutil.rcpath():
                 self.readconfig(f, trust=True)
 
     def copy(self):
         return self.__class__(self)
 
     def formatter(self, topic, opts):
         return formatter.formatter(self, topic, opts)
 
     def _trusted(self, fp, f):
         st = util.fstat(fp)
         if util.isowner(st):
             return True
 
         tusers, tgroups = self._trustusers, self._trustgroups
         if '*' in tusers or '*' in tgroups:
             return True
 
         user = util.username(st.st_uid)
         group = util.groupname(st.st_gid)
         if user in tusers or group in tgroups or user == util.username():
             return True
 
         if self._reportuntrusted:
             self.warn(_('not trusting file %s from untrusted '
                         'user %s, group %s\n') % (f, user, group))
         return False
 
     def readconfig(self, filename, root=None, trust=False,
                    sections=None, remap=None):
         try:
             fp = open(filename)
         except IOError:
             if not sections: # ignore unless we were looking for something
                 return
             raise
 
         cfg = config.config()
         trusted = sections or trust or self._trusted(fp, filename)
 
         try:
             cfg.read(filename, fp, sections=sections, remap=remap)
             fp.close()
         except error.ConfigError, inst:
             if trusted:
                 raise
             self.warn(_("ignored: %s\n") % str(inst))
 
         if self.plain():
             for k in ('debug', 'fallbackencoding', 'quiet', 'slash',
                       'logtemplate', 'statuscopies', 'style',
                       'traceback', 'verbose'):
                 if k in cfg['ui']:
                     del cfg['ui'][k]
             for k, v in cfg.items('defaults'):
                 del cfg['defaults'][k]
         # Don't remove aliases from the configuration if in the exceptionlist
         if self.plain('alias'):
             for k, v in cfg.items('alias'):
                 del cfg['alias'][k]
         if self.plain('revsetalias'):
             for k, v in cfg.items('revsetalias'):
                 del cfg['revsetalias'][k]
 
         if trusted:
             self._tcfg.update(cfg)
             self._tcfg.update(self._ocfg)
         self._ucfg.update(cfg)
         self._ucfg.update(self._ocfg)
 
         if root is None:
             root = os.path.expanduser('~')
         self.fixconfig(root=root)
 
     def fixconfig(self, root=None, section=None):
         if section in (None, 'paths'):
             # expand vars and ~
             # translate paths relative to root (or home) into absolute paths
             root = root or os.getcwd()
             for c in self._tcfg, self._ucfg, self._ocfg:
                 for n, p in c.items('paths'):
                     if not p:
                         continue
                     if '%%' in p:
                         self.warn(_("(deprecated '%%' in path %s=%s from %s)\n")
                                   % (n, p, self.configsource('paths', n)))
                         p = p.replace('%%', '%')
                     p = util.expandpath(p)
                     if not util.hasscheme(p) and not os.path.isabs(p):
                         p = os.path.normpath(os.path.join(root, p))
                     c.set("paths", n, p)
 
         if section in (None, 'ui'):
             # update ui options
             self.debugflag = self.configbool('ui', 'debug')
             self.verbose = self.debugflag or self.configbool('ui', 'verbose')
             self.quiet = not self.debugflag and self.configbool('ui', 'quiet')
             if self.verbose and self.quiet:
                 self.quiet = self.verbose = False
             self._reportuntrusted = self.debugflag or self.configbool("ui",
                 "report_untrusted", True)
             self.tracebackflag = self.configbool('ui', 'traceback', False)
 
         if section in (None, 'trusted'):
             # update trust information
             self._trustusers.update(self.configlist('trusted', 'users'))
             self._trustgroups.update(self.configlist('trusted', 'groups'))
 
     def backupconfig(self, section, item):
         return (self._ocfg.backup(section, item),
                 self._tcfg.backup(section, item),
                 self._ucfg.backup(section, item),)
     def restoreconfig(self, data):
         self._ocfg.restore(data[0])
         self._tcfg.restore(data[1])
         self._ucfg.restore(data[2])
 
     def setconfig(self, section, name, value, source=''):
         for cfg in (self._ocfg, self._tcfg, self._ucfg):
             cfg.set(section, name, value, source)
         self.fixconfig(section=section)
 
     def _data(self, untrusted):
         return untrusted and self._ucfg or self._tcfg
 
     def configsource(self, section, name, untrusted=False):
         return self._data(untrusted).source(section, name) or 'none'
 
     def config(self, section, name, default=None, untrusted=False):
         if isinstance(name, list):
             alternates = name
         else:
             alternates = [name]
 
         for n in alternates:
             value = self._data(untrusted).get(section, n, None)
             if value is not None:
                 name = n
                 break
         else:
             value = default
 
         if self.debugflag and not untrusted and self._reportuntrusted:
             for n in alternates:
                 uvalue = self._ucfg.get(section, n)
                 if uvalue is not None and uvalue != value:
                     self.debug("ignoring untrusted configuration option "
                                "%s.%s = %s\n" % (section, n, uvalue))
         return value
 
     def configpath(self, section, name, default=None, untrusted=False):
         'get a path config item, expanded relative to repo root or config file'
         v = self.config(section, name, default, untrusted)
         if v is None:
             return None
         if not os.path.isabs(v) or "://" not in v:
             src = self.configsource(section, name, untrusted)
             if ':' in src:
                 base = os.path.dirname(src.rsplit(':')[0])
                 v = os.path.join(base, os.path.expanduser(v))
         return v
 
     def configbool(self, section, name, default=False, untrusted=False):
         """parse a configuration element as a boolean
 
         >>> u = ui(); s = 'foo'
         >>> u.setconfig(s, 'true', 'yes')
         >>> u.configbool(s, 'true')
         True
         >>> u.setconfig(s, 'false', 'no')
         >>> u.configbool(s, 'false')
         False
         >>> u.configbool(s, 'unknown')
         False
         >>> u.configbool(s, 'unknown', True)
         True
         >>> u.setconfig(s, 'invalid', 'somevalue')
         >>> u.configbool(s, 'invalid')
         Traceback (most recent call last):
             ...
         ConfigError: foo.invalid is not a boolean ('somevalue')
         """
 
         v = self.config(section, name, None, untrusted)
         if v is None:
             return default
         if isinstance(v, bool):
             return v
         b = util.parsebool(v)
         if b is None:
             raise error.ConfigError(_("%s.%s is not a boolean ('%s')")
                                     % (section, name, v))
         return b
 
     def configint(self, section, name, default=None, untrusted=False):
         """parse a configuration element as an integer
 
         >>> u = ui(); s = 'foo'
         >>> u.setconfig(s, 'int1', '42')
         >>> u.configint(s, 'int1')
         42
         >>> u.setconfig(s, 'int2', '-42')
         >>> u.configint(s, 'int2')
         -42
         >>> u.configint(s, 'unknown', 7)
         7
         >>> u.setconfig(s, 'invalid', 'somevalue')
         >>> u.configint(s, 'invalid')
         Traceback (most recent call last):
             ...
         ConfigError: foo.invalid is not an integer ('somevalue')
         """
 
         v = self.config(section, name, None, untrusted)
         if v is None:
             return default
         try:
             return int(v)
         except ValueError:
             raise error.ConfigError(_("%s.%s is not an integer ('%s')")
                                     % (section, name, v))
 
     def configbytes(self, section, name, default=0, untrusted=False):
         """parse a configuration element as a quantity in bytes
 
         Units can be specified as b (bytes), k or kb (kilobytes), m or
         mb (megabytes), g or gb (gigabytes).
 
         >>> u = ui(); s = 'foo'
         >>> u.setconfig(s, 'val1', '42')
         >>> u.configbytes(s, 'val1')
         42
         >>> u.setconfig(s, 'val2', '42.5 kb')
         >>> u.configbytes(s, 'val2')
         43520
         >>> u.configbytes(s, 'unknown', '7 MB')
         7340032
         >>> u.setconfig(s, 'invalid', 'somevalue')
         >>> u.configbytes(s, 'invalid')
         Traceback (most recent call last):
             ...
         ConfigError: foo.invalid is not a byte quantity ('somevalue')
         """
 
         value = self.config(section, name)
         if value is None:
             if not isinstance(default, str):
                 return default
             value = default
         try:
             return util.sizetoint(value)
         except error.ParseError:
             raise error.ConfigError(_("%s.%s is not a byte quantity ('%s')")
                                     % (section, name, value))
 
     def configlist(self, section, name, default=None, untrusted=False):
         """parse a configuration element as a list of comma/space separated
         strings
 
         >>> u = ui(); s = 'foo'
         >>> u.setconfig(s, 'list1', 'this,is "a small" ,test')
         >>> u.configlist(s, 'list1')
         ['this', 'is', 'a small', 'test']
         """
 
         def _parse_plain(parts, s, offset):
             whitespace = False
             while offset < len(s) and (s[offset].isspace() or s[offset] == ','):
                 whitespace = True
                 offset += 1
             if offset >= len(s):
                 return None, parts, offset
             if whitespace:
                 parts.append('')
             if s[offset] == '"' and not parts[-1]:
                 return _parse_quote, parts, offset + 1
             elif s[offset] == '"' and parts[-1][-1] == '\\':
                 parts[-1] = parts[-1][:-1] + s[offset]
                 return _parse_plain, parts, offset + 1
             parts[-1] += s[offset]
             return _parse_plain, parts, offset + 1
 
         def _parse_quote(parts, s, offset):
             if offset < len(s) and s[offset] == '"': # ""
                 parts.append('')
                 offset += 1
                 while offset < len(s) and (s[offset].isspace() or
                         s[offset] == ','):
                     offset += 1
                 return _parse_plain, parts, offset
 
             while offset < len(s) and s[offset] != '"':
                 if (s[offset] == '\\' and offset + 1 < len(s)
                         and s[offset + 1] == '"'):
                     offset += 1
                     parts[-1] += '"'
                 else:
                     parts[-1] += s[offset]
                 offset += 1
 
             if offset >= len(s):
                 real_parts = _configlist(parts[-1])
                 if not real_parts:
                     parts[-1] = '"'
                 else:
                     real_parts[0] = '"' + real_parts[0]
                     parts = parts[:-1]
                     parts.extend(real_parts)
                 return None, parts, offset
 
             offset += 1
             while offset < len(s) and s[offset] in [' ', ',']:
                 offset += 1
 
             if offset < len(s):
                 if offset + 1 == len(s) and s[offset] == '"':
                     parts[-1] += '"'
                     offset += 1
                 else:
                     parts.append('')
             else:
                 return None, parts, offset
 
             return _parse_plain, parts, offset
 
         def _configlist(s):
             s = s.rstrip(' ,')
             if not s:
                 return []
             parser, parts, offset = _parse_plain, [''], 0
             while parser:
                 parser, parts, offset = parser(parts, s, offset)
             return parts
 
         result = self.config(section, name, untrusted=untrusted)
         if result is None:
             result = default or []
         if isinstance(result, basestring):
             result = _configlist(result.lstrip(' ,\n'))
             if result is None:
                 result = default or []
         return result
 
     def has_section(self, section, untrusted=False):
         '''tell whether section exists in config.'''
         return section in self._data(untrusted)
 
     def configitems(self, section, untrusted=False):
         items = self._data(untrusted).items(section)
         if self.debugflag and not untrusted and self._reportuntrusted:
             for k, v in self._ucfg.items(section):
                 if self._tcfg.get(section, k) != v:
                     self.debug("ignoring untrusted configuration option "
                                "%s.%s = %s\n" % (section, k, v))
         return items
 
     def walkconfig(self, untrusted=False):
         cfg = self._data(untrusted)
         for section in cfg.sections():
             for name, value in self.configitems(section, untrusted):
                 yield section, name, value
 
     def plain(self, feature=None):
         '''is plain mode active?
 
         Plain mode means that all configuration variables which affect
         the behavior and output of Mercurial should be
         ignored. Additionally, the output should be stable,
         reproducible and suitable for use in scripts or applications.
 
         The only way to trigger plain mode is by setting either the
         `HGPLAIN' or `HGPLAINEXCEPT' environment variables.
 
         The return value can either be
         - False if HGPLAIN is not set, or feature is in HGPLAINEXCEPT
         - True otherwise
         '''
         if 'HGPLAIN' not in os.environ and 'HGPLAINEXCEPT' not in os.environ:
             return False
         exceptions = os.environ.get('HGPLAINEXCEPT', '').strip().split(',')
         if feature and exceptions:
             return feature not in exceptions
         return True
 
     def username(self):
         """Return default username to be used in commits.
 
         Searched in this order: $HGUSER, [ui] section of hgrcs, $EMAIL
         and stop searching if one of these is set.
         If not found and ui.askusername is True, ask the user, else use
         ($LOGNAME or $USER or $LNAME or $USERNAME) + "@full.hostname".
         """
         user = os.environ.get("HGUSER")
         if user is None:
             user = self.config("ui", ["username", "user"])
             if user is not None:
                 user = os.path.expandvars(user)
         if user is None:
             user = os.environ.get("EMAIL")
         if user is None and self.configbool("ui", "askusername"):
             user = self.prompt(_("enter a commit username:"), default=None)
         if user is None and not self.interactive():
             try:
                 user = '%s@%s' % (util.getuser(), socket.getfqdn())
                 self.warn(_("no username found, using '%s' instead\n") % user)
             except KeyError:
                 pass
         if not user:
             raise util.Abort(_('no username supplied'),
                              hint=_('use "hg config --edit" '
                                     'to set your username'))
         if "\n" in user:
             raise util.Abort(_("username %s contains a newline\n") % repr(user))
         return user
 
     def shortuser(self, user):
         """Return a short representation of a user name or email address."""
         if not self.verbose:
             user = util.shortuser(user)
         return user
 
     def expandpath(self, loc, default=None):
         """Return repository location relative to cwd or from [paths]"""
         if util.hasscheme(loc) or os.path.isdir(os.path.join(loc, '.hg')):
             return loc
 
         p = self.paths.getpath(loc, default=default)
         if p:
             return p.loc
         return loc
 
     @util.propertycache
     def paths(self):
         return paths(self)
 
     def pushbuffer(self, error=False, subproc=False):
         """install a buffer to capture standard output of the ui object
 
         If error is True, the error output will be captured too.
 
         If subproc is True, output from subprocesses (typically hooks) will be
         captured too."""
         self._buffers.append([])
         self._bufferstates.append((error, subproc))
 
     def popbuffer(self, labeled=False):
         '''pop the last buffer and return the buffered output
 
         If labeled is True, any labels associated with buffered
         output will be handled. By default, this has no effect
         on the output returned, but extensions and GUI tools may
         handle this argument and returned styled output. If output
         is being buffered so it can be captured and parsed or
         processed, labeled should not be set to True.
         '''
         self._bufferstates.pop()
         return "".join(self._buffers.pop())
 
     def write(self, *args, **opts):
         '''write args to output
 
         By default, this method simply writes to the buffer or stdout,
         but extensions or GUI tools may override this method,
         write_err(), popbuffer(), and label() to style output from
         various parts of hg.
 
         An optional keyword argument, "label", can be passed in.
         This should be a string containing label names separated by
         space. Label names take the form of "topic.type". For example,
         ui.debug() issues a label of "ui.debug".
 
         When labeling output for a specific command, a label of
         "cmdname.type" is recommended. For example, status issues
         a label of "status.modified" for modified files.
         '''
         self._progclear()
         if self._buffers:
             self._buffers[-1].extend([str(a) for a in args])
         else:
             for a in args:
                 self.fout.write(str(a))
 
     def write_err(self, *args, **opts):
         self._progclear()
         try:
             if self._bufferstates and self._bufferstates[-1][0]:
                 return self.write(*args, **opts)
             if not getattr(self.fout, 'closed', False):
                 self.fout.flush()
             for a in args:
                 self.ferr.write(str(a))
             # stderr may be buffered under win32 when redirected to files,
             # including stdout.
             if not getattr(self.ferr, 'closed', False):
                 self.ferr.flush()
         except IOError, inst:
             if inst.errno not in (errno.EPIPE, errno.EIO, errno.EBADF):
                 raise
 
     def flush(self):
         try: self.fout.flush()
         except (IOError, ValueError): pass
         try: self.ferr.flush()
         except (IOError, ValueError): pass
 
     def _isatty(self, fh):
         if self.configbool('ui', 'nontty', False):
             return False
         return util.isatty(fh)
 
     def interactive(self):
         '''is interactive input allowed?
 
         An interactive session is a session where input can be reasonably read
         from `sys.stdin'. If this function returns false, any attempt to read
         from stdin should fail with an error, unless a sensible default has been
         specified.
 
         Interactiveness is triggered by the value of the `ui.interactive'
         configuration variable or - if it is unset - when `sys.stdin' points
         to a terminal device.
 
         This function refers to input only; for output, see `ui.formatted()'.
         '''
         i = self.configbool("ui", "interactive", None)
         if i is None:
             # some environments replace stdin without implementing isatty
             # usually those are non-interactive
             return self._isatty(self.fin)
 
         return i
 
     def termwidth(self):
         '''how wide is the terminal in columns?
         '''
         if 'COLUMNS' in os.environ:
             try:
                 return int(os.environ['COLUMNS'])
             except ValueError:
                 pass
         return util.termwidth()
 
     def formatted(self):
         '''should formatted output be used?
 
         It is often desirable to format the output to suite the output medium.
         Examples of this are truncating long lines or colorizing messages.
         However, this is not often not desirable when piping output into other
         utilities, e.g. `grep'.
 
         Formatted output is triggered by the value of the `ui.formatted'
         configuration variable or - if it is unset - when `sys.stdout' points
         to a terminal device. Please note that `ui.formatted' should be
         considered an implementation detail; it is not intended for use outside
         Mercurial or its extensions.
 
         This function refers to output only; for input, see `ui.interactive()'.
         This function always returns false when in plain mode, see `ui.plain()'.
         '''
         if self.plain():
             return False
 
         i = self.configbool("ui", "formatted", None)
         if i is None:
             # some environments replace stdout without implementing isatty
             # usually those are non-interactive
             return self._isatty(self.fout)
 
         return i
 
     def _readline(self, prompt=''):
         if self._isatty(self.fin):
             try:
                 # magically add command line editing support, where
                 # available
                 import readline
                 # force demandimport to really load the module
                 readline.read_history_file
                 # windows sometimes raises something other than ImportError
             except Exception:
                 pass
 
         # call write() so output goes through subclassed implementation
         # e.g. color extension on Windows
         self.write(prompt)
 
         # instead of trying to emulate raw_input, swap (self.fin,
         # self.fout) with (sys.stdin, sys.stdout)
         oldin = sys.stdin
         oldout = sys.stdout
         sys.stdin = self.fin
         sys.stdout = self.fout
         # prompt ' ' must exist; otherwise readline may delete entire line
         # - http://bugs.python.org/issue12833
         line = raw_input(' ')
         sys.stdin = oldin
         sys.stdout = oldout
 
         # When stdin is in binary mode on Windows, it can cause
         # raw_input() to emit an extra trailing carriage return
         if os.linesep == '\r\n' and line and line[-1] == '\r':
             line = line[:-1]
         return line
 
     def prompt(self, msg, default="y"):
         """Prompt user with msg, read response.
         If ui is not interactive, the default is returned.
         """
         if not self.interactive():
             self.write(msg, ' ', default, "\n")
             return default
         try:
             r = self._readline(self.label(msg, 'ui.prompt'))
             if not r:
                 r = default
             if self.configbool('ui', 'promptecho'):
                 self.write(r, "\n")
             return r
         except EOFError:
             raise util.Abort(_('response expected'))
 
     @staticmethod
     def extractchoices(prompt):
         """Extract prompt message and list of choices from specified prompt.
 
         This returns tuple "(message, choices)", and "choices" is the
         list of tuple "(response character, text without &)".
         """
         parts = prompt.split('$$')
         msg = parts[0].rstrip(' ')
         choices = [p.strip(' ') for p in parts[1:]]
         return (msg,
                 [(s[s.index('&') + 1].lower(), s.replace('&', '', 1))
                  for s in choices])
 
     def promptchoice(self, prompt, default=0):
         """Prompt user with a message, read response, and ensure it matches
         one of the provided choices. The prompt is formatted as follows:
 
            "would you like fries with that (Yn)? $$ &Yes $$ &No"
 
         The index of the choice is returned. Responses are case
         insensitive. If ui is not interactive, the default is
         returned.
         """
 
         msg, choices = self.extractchoices(prompt)
         resps = [r for r, t in choices]
         while True:
             r = self.prompt(msg, resps[default])
             if r.lower() in resps:
                 return resps.index(r.lower())
             self.write(_("unrecognized response\n"))
 
     def getpass(self, prompt=None, default=None):
         if not self.interactive():
             return default
         try:
             self.write_err(self.label(prompt or _('password: '), 'ui.prompt'))
             # disable getpass() only if explicitly specified. it's still valid
             # to interact with tty even if fin is not a tty.
             if self.configbool('ui', 'nontty'):
                 return self.fin.readline().rstrip('\n')
             else:
                 return getpass.getpass('')
         except EOFError:
             raise util.Abort(_('response expected'))
     def status(self, *msg, **opts):
         '''write status message to output (if ui.quiet is False)
 
         This adds an output label of "ui.status".
         '''
         if not self.quiet:
             opts['label'] = opts.get('label', '') + ' ui.status'
             self.write(*msg, **opts)
     def warn(self, *msg, **opts):
         '''write warning message to output (stderr)
 
         This adds an output label of "ui.warning".
         '''
         opts['label'] = opts.get('label', '') + ' ui.warning'
         self.write_err(*msg, **opts)
     def note(self, *msg, **opts):
         '''write note to output (if ui.verbose is True)
 
         This adds an output label of "ui.note".
         '''
         if self.verbose:
             opts['label'] = opts.get('label', '') + ' ui.note'
             self.write(*msg, **opts)
     def debug(self, *msg, **opts):
         '''write debug message to output (if ui.debugflag is True)
 
         This adds an output label of "ui.debug".
         '''
         if self.debugflag:
             opts['label'] = opts.get('label', '') + ' ui.debug'
             self.write(*msg, **opts)
     def edit(self, text, user, extra={}, editform=None):
         (fd, name) = tempfile.mkstemp(prefix="hg-editor-", suffix=".txt",
                                       text=True)
         try:
             f = os.fdopen(fd, "w")
             f.write(text)
             f.close()
 
             environ = {'HGUSER': user}
             if 'transplant_source' in extra:
                 environ.update({'HGREVISION': hex(extra['transplant_source'])})
             for label in ('intermediate-source', 'source', 'rebase_source'):
                 if label in extra:
                     environ.update({'HGREVISION': extra[label]})
                     break
             if editform:
                 environ.update({'HGEDITFORM': editform})
 
             editor = self.geteditor()
 
             self.system("%s \"%s\"" % (editor, name),
                         environ=environ,
                         onerr=util.Abort, errprefix=_("edit failed"))
 
             f = open(name)
             t = f.read()
             f.close()
         finally:
             os.unlink(name)
 
         return t
 
     def system(self, cmd, environ={}, cwd=None, onerr=None, errprefix=None):
         '''execute shell command with appropriate output stream. command
         output will be redirected if fout is not stdout.
         '''
         out = self.fout
         if any(s[1] for s in self._bufferstates):
             out = self
         return util.system(cmd, environ=environ, cwd=cwd, onerr=onerr,
                            errprefix=errprefix, out=out)
 
     def traceback(self, exc=None, force=False):
         '''print exception traceback if traceback printing enabled or forced.
         only to call in exception handler. returns true if traceback
         printed.'''
         if self.tracebackflag or force:
             if exc is None:
                 exc = sys.exc_info()
             cause = getattr(exc[1], 'cause', None)
 
             if cause is not None:
                 causetb = traceback.format_tb(cause[2])
                 exctb = traceback.format_tb(exc[2])
                 exconly = traceback.format_exception_only(cause[0], cause[1])
 
                 # exclude frame where 'exc' was chained and rethrown from exctb
                 self.write_err('Traceback (most recent call last):\n',
                                ''.join(exctb[:-1]),
                                ''.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):
         '''return editor to use'''
         if sys.platform == 'plan9':
             # vi is the MIPS instruction simulator on Plan 9. We
             # instead default to E to plumb commit messages to
             # avoid confusion.
             editor = 'E'
         else:
             editor = 'vi'
         return (os.environ.get("HGEDITOR") or
                 self.config("ui", "editor") or
                 os.environ.get("VISUAL") or
                 os.environ.get("EDITOR", editor))
 
     @util.propertycache
     def _progbar(self):
         """setup the progbar singleton to the ui object"""
         if (self.quiet or self.debugflag
                 or self.configbool('progress', 'disable', False)
                 or not progress.shouldprint(self)):
             return None
         return getprogbar(self)
 
     def _progclear(self):
         """clear progress bar output if any. use it before any output"""
         if '_progbar' not in vars(self): # nothing loadef yet
             return
         if self._progbar is not None and self._progbar.printed:
             self._progbar.clear()
 
     def progress(self, topic, pos, item="", unit="", total=None):
         '''show a progress message
 
         With stock hg, this is simply a debug message that is hidden
         by default, but with extensions or GUI tools it may be
         visible. 'topic' is the current operation, 'item' is a
         non-numeric marker of the current position (i.e. the currently
         in-process file), 'pos' is the current numeric position (i.e.
         revision, bytes, etc.), unit is a corresponding unit label,
         and total is the highest expected pos.
 
         Multiple nested topics may be active at a time.
 
         All topics should be marked closed by setting pos to None at
         termination.
         '''
         if self._progbar is not None:
             self._progbar.progress(topic, pos, item=item, unit=unit,
                                    total=total)
         if pos is None or not self.configbool('progress', 'debug'):
             return
 
         if unit:
             unit = ' ' + unit
         if item:
             item = ' ' + item
 
         if total:
             pct = 100.0 * pos / total
             self.debug('%s:%s %s/%s%s (%4.2f%%)\n'
                      % (topic, item, pos, total, unit, pct))
         else:
             self.debug('%s:%s %s%s\n' % (topic, item, pos, unit))
 
     def log(self, service, *msg, **opts):
         '''hook for logging facility extensions
 
         service should be a readily-identifiable subsystem, which will
         allow filtering.
         message should be a newline-terminated string to log.
         '''
         pass
 
     def label(self, msg, label):
         '''style msg based on supplied label
 
         Like ui.write(), this just returns msg unchanged, but extensions
         and GUI tools can override it to allow styling output without
         writing it.
 
         ui.write(s, 'label') is equivalent to
         ui.write(ui.label(s, 'label')).
         '''
         return msg
 
 class paths(dict):
     """Represents a collection of paths and their configs.
 
     Data is initially derived from ui instances and the config files they have
     loaded.
     """
     def __init__(self, ui):
         dict.__init__(self)
 
         for name, loc in ui.configitems('paths'):
             # No location is the same as not existing.
             if not loc:
                 continue
             self[name] = path(name, rawloc=loc)
 
     def getpath(self, name, default=None):
         """Return a ``path`` for the specified name, falling back to a default.
 
         Returns the first of ``name`` or ``default`` that is present, or None
         if neither is present.
         """
         try:
             return self[name]
         except KeyError:
             if default is not None:
                 try:
                     return self[default]
                 except KeyError:
                     pass
 
         return None
 
 class path(object):
     """Represents an individual path and its configuration."""
 
     def __init__(self, name, rawloc=None):
         """Construct a path from its config options.
 
         ``name`` is the symbolic name of the path.
         ``rawloc`` is the raw location, as defined in the config.
         """
         self.name = name
         # We'll do more intelligent things with rawloc in the future.
         self.loc = rawloc
 
 # we instantiate one globally shared progress bar to avoid
 # competing progress bars when multiple UI objects get created
 _progresssingleton = None
 
 def getprogbar(ui):
     global _progresssingleton
     if _progresssingleton is None:
         # passing 'ui' object to the singleton is fishy,
         # this is how the extension used to work but feel free to rework it.
         _progresssingleton = progress.progbar(ui)
     return _progresssingleton