pager: don't terminate with extreme prejudice on SIGPIPE (BC)

The default SIGPIPE handler causes Mercurial to exit immediately, without
running any Python cleanup code (except and finally blocks, atexit handlers
etc). This creates problems if you want to do something at exit.

If we need a different exit code for broken pipe from pager, then we should
code that ourselves in Python; this appears to have been cargo-culted from
the fork implementation of pager that's no longer used, where it was needed
to stop Broken Pipe errors appearing on the user's terminal.

hgext/pager.py

@@ -1,174 +1,172 b''
 # pager.py - display output using a pager
 #
 # Copyright 2008 David Soria Parra <[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.
 #
 # To load the extension, add it to your configuration file:
 #
 #   [extension]
 #   pager =
 #
 # Run 'hg help pager' to get info on configuration.
 
 '''browse command output with an external pager
 
 To set the pager that should be used, set the application variable::
 
   [pager]
   pager = less -FRX
 
 If no pager is set, the pager extensions uses the environment variable
 $PAGER. If neither pager.pager, nor $PAGER is set, no pager is used.
 
 You can disable the pager for certain commands by adding them to the
 pager.ignore list::
 
   [pager]
   ignore = version, help, update
 
 You can also enable the pager only for certain commands using
 pager.attend. Below is the default list of commands to be paged::
 
   [pager]
   attend = annotate, cat, diff, export, glog, log, qdiff
 
 Setting pager.attend to an empty value will cause all commands to be
 paged.
 
 If pager.attend is present, pager.ignore will be ignored.
 
 Lastly, you can enable and disable paging for individual commands with
 the attend-<command> option. This setting takes precedence over
 existing attend and ignore options and defaults::
 
   [pager]
   attend-cat = false
 
 To ignore global commands like :hg:`version` or :hg:`help`, you have
 to specify them in your user configuration file.
 
 To control whether the pager is used at all for an individual command,
 you can use --pager=<value>::
 
   - use as needed: `auto`.
   - require the pager: `yes` or `on`.
   - suppress the pager: `no` or `off` (any unrecognized value
   will also work).
 
 '''
 from __future__ import absolute_import
 
 import atexit
 import os
 import signal
 import subprocess
 import sys
 
 from mercurial.i18n import _
 from mercurial import (
     cmdutil,
     commands,
     dispatch,
     encoding,
     extensions,
     util,
     )
 
 # Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
 # extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
 # be specifying the version(s) of Mercurial they are tested with, or
 # leave the attribute unspecified.
 testedwith = 'ships-with-hg-core'
 
 def _runpager(ui, p):
     pager = subprocess.Popen(p, shell=True, bufsize=-1,
                              close_fds=util.closefds, stdin=subprocess.PIPE,
                              stdout=util.stdout, stderr=util.stderr)
 
     # back up original file objects and descriptors
     olduifout = ui.fout
     oldstdout = util.stdout
     stdoutfd = os.dup(util.stdout.fileno())
     stderrfd = os.dup(util.stderr.fileno())
 
     # create new line-buffered stdout so that output can show up immediately
     ui.fout = util.stdout = newstdout = os.fdopen(util.stdout.fileno(), 'wb', 1)
     os.dup2(pager.stdin.fileno(), util.stdout.fileno())
     if ui._isatty(util.stderr):
         os.dup2(pager.stdin.fileno(), util.stderr.fileno())
 
     @atexit.register
     def killpager():
         if util.safehasattr(signal, "SIGINT"):
             signal.signal(signal.SIGINT, signal.SIG_IGN)
         pager.stdin.close()
         ui.fout = olduifout
         util.stdout = oldstdout
         # close new stdout while it's associated with pager; otherwise stdout
         # fd would be closed when newstdout is deleted
         newstdout.close()
         # restore original fds: stdout is open again
         os.dup2(stdoutfd, util.stdout.fileno())
         os.dup2(stderrfd, util.stderr.fileno())
         pager.wait()
 
 def uisetup(ui):
     class pagerui(ui.__class__):
         def _runpager(self, pagercmd):
             _runpager(self, pagercmd)
 
     ui.__class__ = pagerui
 
     def pagecmd(orig, ui, options, cmd, cmdfunc):
         p = ui.config("pager", "pager", encoding.environ.get("PAGER"))
         usepager = False
         always = util.parsebool(options['pager'])
         auto = options['pager'] == 'auto'
 
         if not p or '--debugger' in sys.argv or not ui.formatted():
             pass
         elif always:
             usepager = True
         elif not auto:
             usepager = False
         else:
             attend = ui.configlist('pager', 'attend', attended)
             ignore = ui.configlist('pager', 'ignore')
             cmds, _ = cmdutil.findcmd(cmd, commands.table)
 
             for cmd in cmds:
                 var = 'attend-%s' % cmd
                 if ui.config('pager', var):
                     usepager = ui.configbool('pager', var)
                     break
                 if (cmd in attend or
                      (cmd not in ignore and not attend)):
                     usepager = True
                     break
 
         setattr(ui, 'pageractive', usepager)
 
         if usepager:
             ui.setconfig('ui', 'formatted', ui.formatted(), 'pager')
             ui.setconfig('ui', 'interactive', False, 'pager')
-            if util.safehasattr(signal, "SIGPIPE"):
-                signal.signal(signal.SIGPIPE, signal.SIG_DFL)
             ui._runpager(p)
         return orig(ui, options, cmd, cmdfunc)
 
     # Wrap dispatch._runcommand after color is loaded so color can see
     # ui.pageractive. Otherwise, if we loaded first, color's wrapped
     # dispatch._runcommand would run without having access to ui.pageractive.
     def afterloaded(loaded):
         extensions.wrapfunction(dispatch, '_runcommand', pagecmd)
     extensions.afterloaded('color', afterloaded)
 
 def extsetup(ui):
     commands.globalopts.append(
         ('', 'pager', 'auto',
          _("when to paginate (boolean, always, auto, or never)"),
          _('TYPE')))
 
 attended = ['annotate', 'cat', 'diff', 'export', 'glog', 'log', 'qdiff']