pager: exit cleanly on SIGPIPE (BC)

Changeset aaa751585325 removes SIGPIPE handling completely. This is wrong,
as it means that Mercurial does not exit when the pager does. Instead, raise
SignalInterrupt when SIGPIPE happens with a pager attached, to trigger the
normal exit path.

This will cause "killed!" to be printed to stderr (hence the BC warning),
but in the normal pager use case (where the pager gets both stderr and
stdout), this message is lost as we only get SIGPIPE when the pager quits.

hgext/pager.py

@@ -1,163 +1,169 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,
+    error,
     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 descriptors
     stdoutfd = os.dup(util.stdout.fileno())
     stderrfd = os.dup(util.stderr.fileno())
 
     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)
         # restore original fds, closing pager.stdin copies in the process
         os.dup2(stdoutfd, util.stdout.fileno())
         os.dup2(stderrfd, util.stderr.fileno())
         pager.stdin.close()
         pager.wait()
 
+def catchterm(*args):
+    raise error.SignalInterrupt
+
 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, catchterm)
             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']