filemerge: explicitly tests for None

Changeset 758526333dec removed the mutable default value, but did not explicitly
tested for None. Such implicit testing can introduce semantic and performance
issue. We move to an explicit testing for None as recommended by PEP8:

https://www.python.org/dev/peps/pep-0008/#programming-recommendations

mercurial/filemerge.py

@@ -1,718 +1,720 b''
 # filemerge.py - file-level merge handling for Mercurial
 #
 # Copyright 2006, 2007, 2008 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 __future__ import absolute_import
 
 import filecmp
 import os
 import re
 import tempfile
 
 from .i18n import _
 from .node import nullid, short
 
 from . import (
     encoding,
     error,
     formatter,
     match,
     pycompat,
     scmutil,
     simplemerge,
     tagmerge,
     templatekw,
     templater,
     util,
 )
 
 def _toolstr(ui, tool, part, default=""):
     return ui.config("merge-tools", tool + "." + part, default)
 
 def _toolbool(ui, tool, part, default=False):
     return ui.configbool("merge-tools", tool + "." + part, default)
 
 def _toollist(ui, tool, part, default=None):
-    return ui.configlist("merge-tools", tool + "." + part, default or [])
+    if default is None:
+        default = []
+    return ui.configlist("merge-tools", tool + "." + part, default)
 
 internals = {}
 # Merge tools to document.
 internalsdoc = {}
 
 # internal tool merge types
 nomerge = None
 mergeonly = 'mergeonly'  # just the full merge, no premerge
 fullmerge = 'fullmerge'  # both premerge and merge
 
 class absentfilectx(object):
     """Represents a file that's ostensibly in a context but is actually not
     present in it.
 
     This is here because it's very specific to the filemerge code for now --
     other code is likely going to break with the values this returns."""
     def __init__(self, ctx, f):
         self._ctx = ctx
         self._f = f
 
     def path(self):
         return self._f
 
     def size(self):
         return None
 
     def data(self):
         return None
 
     def filenode(self):
         return nullid
 
     _customcmp = True
     def cmp(self, fctx):
         """compare with other file context
 
         returns True if different from fctx.
         """
         return not (fctx.isabsent() and
                     fctx.ctx() == self.ctx() and
                     fctx.path() == self.path())
 
     def flags(self):
         return ''
 
     def changectx(self):
         return self._ctx
 
     def isbinary(self):
         return False
 
     def isabsent(self):
         return True
 
 def internaltool(name, mergetype, onfailure=None, precheck=None):
     '''return a decorator for populating internal merge tool table'''
     def decorator(func):
         fullname = ':' + name
         func.__doc__ = (pycompat.sysstr("``%s``\n" % fullname)
                         + func.__doc__.strip())
         internals[fullname] = func
         internals['internal:' + name] = func
         internalsdoc[fullname] = func
         func.mergetype = mergetype
         func.onfailure = onfailure
         func.precheck = precheck
         return func
     return decorator
 
 def _findtool(ui, tool):
     if tool in internals:
         return tool
     return findexternaltool(ui, tool)
 
 def findexternaltool(ui, tool):
     for kn in ("regkey", "regkeyalt"):
         k = _toolstr(ui, tool, kn)
         if not k:
             continue
         p = util.lookupreg(k, _toolstr(ui, tool, "regname"))
         if p:
             p = util.findexe(p + _toolstr(ui, tool, "regappend"))
             if p:
                 return p
     exe = _toolstr(ui, tool, "executable", tool)
     return util.findexe(util.expandpath(exe))
 
 def _picktool(repo, ui, path, binary, symlink, changedelete):
     def supportscd(tool):
         return tool in internals and internals[tool].mergetype == nomerge
 
     def check(tool, pat, symlink, binary, changedelete):
         tmsg = tool
         if pat:
             tmsg += " specified for " + pat
         if not _findtool(ui, tool):
             if pat: # explicitly requested tool deserves a warning
                 ui.warn(_("couldn't find merge tool %s\n") % tmsg)
             else: # configured but non-existing tools are more silent
                 ui.note(_("couldn't find merge tool %s\n") % tmsg)
         elif symlink and not _toolbool(ui, tool, "symlink"):
             ui.warn(_("tool %s can't handle symlinks\n") % tmsg)
         elif binary and not _toolbool(ui, tool, "binary"):
             ui.warn(_("tool %s can't handle binary\n") % tmsg)
         elif changedelete and not supportscd(tool):
             # the nomerge tools are the only tools that support change/delete
             # conflicts
             pass
         elif not util.gui() and _toolbool(ui, tool, "gui"):
             ui.warn(_("tool %s requires a GUI\n") % tmsg)
         else:
             return True
         return False
 
     # internal config: ui.forcemerge
     # forcemerge comes from command line arguments, highest priority
     force = ui.config('ui', 'forcemerge')
     if force:
         toolpath = _findtool(ui, force)
         if changedelete and not supportscd(toolpath):
             return ":prompt", None
         else:
             if toolpath:
                 return (force, util.shellquote(toolpath))
             else:
                 # mimic HGMERGE if given tool not found
                 return (force, force)
 
     # HGMERGE takes next precedence
     hgmerge = encoding.environ.get("HGMERGE")
     if hgmerge:
         if changedelete and not supportscd(hgmerge):
             return ":prompt", None
         else:
             return (hgmerge, hgmerge)
 
     # then patterns
     for pat, tool in ui.configitems("merge-patterns"):
         mf = match.match(repo.root, '', [pat])
         if mf(path) and check(tool, pat, symlink, False, changedelete):
             toolpath = _findtool(ui, tool)
             return (tool, util.shellquote(toolpath))
 
     # then merge tools
     tools = {}
     disabled = set()
     for k, v in ui.configitems("merge-tools"):
         t = k.split('.')[0]
         if t not in tools:
             tools[t] = int(_toolstr(ui, t, "priority", "0"))
         if _toolbool(ui, t, "disabled", False):
             disabled.add(t)
     names = tools.keys()
     tools = sorted([(-p, tool) for tool, p in tools.items()
                     if tool not in disabled])
     uimerge = ui.config("ui", "merge")
     if uimerge:
         # external tools defined in uimerge won't be able to handle
         # change/delete conflicts
         if uimerge not in names and not changedelete:
             return (uimerge, uimerge)
         tools.insert(0, (None, uimerge)) # highest priority
     tools.append((None, "hgmerge")) # the old default, if found
     for p, t in tools:
         if check(t, None, symlink, binary, changedelete):
             toolpath = _findtool(ui, t)
             return (t, util.shellquote(toolpath))
 
     # internal merge or prompt as last resort
     if symlink or binary or changedelete:
         return ":prompt", None
     return ":merge", None
 
 def _eoltype(data):
     "Guess the EOL type of a file"
     if '\0' in data: # binary
         return None
     if '\r\n' in data: # Windows
         return '\r\n'
     if '\r' in data: # Old Mac
         return '\r'
     if '\n' in data: # UNIX
         return '\n'
     return None # unknown
 
 def _matcheol(file, origfile):
     "Convert EOL markers in a file to match origfile"
     tostyle = _eoltype(util.readfile(origfile))
     if tostyle:
         data = util.readfile(file)
         style = _eoltype(data)
         if style:
             newdata = data.replace(style, tostyle)
             if newdata != data:
                 util.writefile(file, newdata)
 
 @internaltool('prompt', nomerge)
 def _iprompt(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
     """Asks the user which of the local `p1()` or the other `p2()` version to
     keep as the merged version."""
     ui = repo.ui
     fd = fcd.path()
 
     prompts = partextras(labels)
     prompts['fd'] = fd
     try:
         if fco.isabsent():
             index = ui.promptchoice(
                 _("local%(l)s changed %(fd)s which other%(o)s deleted\n"
                   "use (c)hanged version, (d)elete, or leave (u)nresolved?"
                   "$$ &Changed $$ &Delete $$ &Unresolved") % prompts, 2)
             choice = ['local', 'other', 'unresolved'][index]
         elif fcd.isabsent():
             index = ui.promptchoice(
                 _("other%(o)s changed %(fd)s which local%(l)s deleted\n"
                   "use (c)hanged version, leave (d)eleted, or "
                   "leave (u)nresolved?"
                   "$$ &Changed $$ &Deleted $$ &Unresolved") % prompts, 2)
             choice = ['other', 'local', 'unresolved'][index]
         else:
             index = ui.promptchoice(
                 _("no tool found to merge %(fd)s\n"
                   "keep (l)ocal%(l)s, take (o)ther%(o)s, or leave (u)nresolved?"
                   "$$ &Local $$ &Other $$ &Unresolved") % prompts, 2)
             choice = ['local', 'other', 'unresolved'][index]
 
         if choice == 'other':
             return _iother(repo, mynode, orig, fcd, fco, fca, toolconf,
                            labels)
         elif choice == 'local':
             return _ilocal(repo, mynode, orig, fcd, fco, fca, toolconf,
                            labels)
         elif choice == 'unresolved':
             return _ifail(repo, mynode, orig, fcd, fco, fca, toolconf,
                           labels)
     except error.ResponseExpected:
         ui.write("\n")
         return _ifail(repo, mynode, orig, fcd, fco, fca, toolconf,
                       labels)
 
 @internaltool('local', nomerge)
 def _ilocal(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
     """Uses the local `p1()` version of files as the merged version."""
     return 0, fcd.isabsent()
 
 @internaltool('other', nomerge)
 def _iother(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
     """Uses the other `p2()` version of files as the merged version."""
     if fco.isabsent():
         # local changed, remote deleted -- 'deleted' picked
         repo.wvfs.unlinkpath(fcd.path())
         deleted = True
     else:
         repo.wwrite(fcd.path(), fco.data(), fco.flags())
         deleted = False
     return 0, deleted
 
 @internaltool('fail', nomerge)
 def _ifail(repo, mynode, orig, fcd, fco, fca, toolconf, labels=None):
     """
     Rather than attempting to merge files that were modified on both
     branches, it marks them as unresolved. The resolve command must be
     used to resolve these conflicts."""
     # for change/delete conflicts write out the changed version, then fail
     if fcd.isabsent():
         repo.wwrite(fcd.path(), fco.data(), fco.flags())
     return 1, False
 
 def _premerge(repo, fcd, fco, fca, toolconf, files, labels=None):
     tool, toolpath, binary, symlink = toolconf
     if symlink or fcd.isabsent() or fco.isabsent():
         return 1
     a, b, c, back = files
 
     ui = repo.ui
 
     validkeep = ['keep', 'keep-merge3']
 
     # do we attempt to simplemerge first?
     try:
         premerge = _toolbool(ui, tool, "premerge", not binary)
     except error.ConfigError:
         premerge = _toolstr(ui, tool, "premerge").lower()
         if premerge not in validkeep:
             _valid = ', '.join(["'" + v + "'" for v in validkeep])
             raise error.ConfigError(_("%s.premerge not valid "
                                       "('%s' is neither boolean nor %s)") %
                                     (tool, premerge, _valid))
 
     if premerge:
         if premerge == 'keep-merge3':
             if not labels:
                 labels = _defaultconflictlabels
             if len(labels) < 3:
                 labels.append('base')
         r = simplemerge.simplemerge(ui, a, b, c, quiet=True, label=labels)
         if not r:
             ui.debug(" premerge successful\n")
             return 0
         if premerge not in validkeep:
             util.copyfile(back, a) # restore from backup and try again
     return 1 # continue merging
 
 def _mergecheck(repo, mynode, orig, fcd, fco, fca, toolconf):
     tool, toolpath, binary, symlink = toolconf
     if symlink:
         repo.ui.warn(_('warning: internal %s cannot merge symlinks '
                        'for %s\n') % (tool, fcd.path()))
         return False
     if fcd.isabsent() or fco.isabsent():
         repo.ui.warn(_('warning: internal %s cannot merge change/delete '
                        'conflict for %s\n') % (tool, fcd.path()))
         return False
     return True
 
 def _merge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels, mode):
     """
     Uses the internal non-interactive simple merge algorithm for merging
     files. It will fail if there are any conflicts and leave markers in
     the partially merged file. Markers will have two sections, one for each side
     of merge, unless mode equals 'union' which suppresses the markers."""
     a, b, c, back = files
 
     ui = repo.ui
 
     r = simplemerge.simplemerge(ui, a, b, c, label=labels, mode=mode)
     return True, r, False
 
 @internaltool('union', fullmerge,
               _("warning: conflicts while merging %s! "
                 "(edit, then use 'hg resolve --mark')\n"),
               precheck=_mergecheck)
 def _iunion(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     """
     Uses the internal non-interactive simple merge algorithm for merging
     files. It will use both left and right sides for conflict regions.
     No markers are inserted."""
     return _merge(repo, mynode, orig, fcd, fco, fca, toolconf,
                   files, labels, 'union')
 
 @internaltool('merge', fullmerge,
               _("warning: conflicts while merging %s! "
                 "(edit, then use 'hg resolve --mark')\n"),
               precheck=_mergecheck)
 def _imerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     """
     Uses the internal non-interactive simple merge algorithm for merging
     files. It will fail if there are any conflicts and leave markers in
     the partially merged file. Markers will have two sections, one for each side
     of merge."""
     return _merge(repo, mynode, orig, fcd, fco, fca, toolconf,
                   files, labels, 'merge')
 
 @internaltool('merge3', fullmerge,
               _("warning: conflicts while merging %s! "
                 "(edit, then use 'hg resolve --mark')\n"),
               precheck=_mergecheck)
 def _imerge3(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     """
     Uses the internal non-interactive simple merge algorithm for merging
     files. It will fail if there are any conflicts and leave markers in
     the partially merged file. Marker will have three sections, one from each
     side of the merge and one for the base content."""
     if not labels:
         labels = _defaultconflictlabels
     if len(labels) < 3:
         labels.append('base')
     return _imerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels)
 
 def _imergeauto(repo, mynode, orig, fcd, fco, fca, toolconf, files,
                 labels=None, localorother=None):
     """
     Generic driver for _imergelocal and _imergeother
     """
     assert localorother is not None
     tool, toolpath, binary, symlink = toolconf
     a, b, c, back = files
     r = simplemerge.simplemerge(repo.ui, a, b, c, label=labels,
                                 localorother=localorother)
     return True, r
 
 @internaltool('merge-local', mergeonly, precheck=_mergecheck)
 def _imergelocal(*args, **kwargs):
     """
     Like :merge, but resolve all conflicts non-interactively in favor
     of the local `p1()` changes."""
     success, status = _imergeauto(localorother='local', *args, **kwargs)
     return success, status, False
 
 @internaltool('merge-other', mergeonly, precheck=_mergecheck)
 def _imergeother(*args, **kwargs):
     """
     Like :merge, but resolve all conflicts non-interactively in favor
     of the other `p2()` changes."""
     success, status = _imergeauto(localorother='other', *args, **kwargs)
     return success, status, False
 
 @internaltool('tagmerge', mergeonly,
               _("automatic tag merging of %s failed! "
                 "(use 'hg resolve --tool :merge' or another merge "
                 "tool of your choice)\n"))
 def _itagmerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     """
     Uses the internal tag merge algorithm (experimental).
     """
     success, status = tagmerge.merge(repo, fcd, fco, fca)
     return success, status, False
 
 @internaltool('dump', fullmerge)
 def _idump(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     """
     Creates three versions of the files to merge, containing the
     contents of local, other and base. These files can then be used to
     perform a merge manually. If the file to be merged is named
     ``a.txt``, these files will accordingly be named ``a.txt.local``,
     ``a.txt.other`` and ``a.txt.base`` and they will be placed in the
     same directory as ``a.txt``."""
     a, b, c, back = files
 
     fd = fcd.path()
 
     util.copyfile(a, a + ".local")
     repo.wwrite(fd + ".other", fco.data(), fco.flags())
     repo.wwrite(fd + ".base", fca.data(), fca.flags())
     return False, 1, False
 
 def _xmerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     tool, toolpath, binary, symlink = toolconf
     if fcd.isabsent() or fco.isabsent():
         repo.ui.warn(_('warning: %s cannot merge change/delete conflict '
                        'for %s\n') % (tool, fcd.path()))
         return False, 1, None
     a, b, c, back = files
     out = ""
     env = {'HG_FILE': fcd.path(),
            'HG_MY_NODE': short(mynode),
            'HG_OTHER_NODE': str(fco.changectx()),
            'HG_BASE_NODE': str(fca.changectx()),
            'HG_MY_ISLINK': 'l' in fcd.flags(),
            'HG_OTHER_ISLINK': 'l' in fco.flags(),
            'HG_BASE_ISLINK': 'l' in fca.flags(),
            }
 
     ui = repo.ui
 
     args = _toolstr(ui, tool, "args", '$local $base $other')
     if "$output" in args:
         out, a = a, back # read input from backup, write to original
     replace = {'local': a, 'base': b, 'other': c, 'output': out}
     args = util.interpolate(r'\$', replace, args,
                             lambda s: util.shellquote(util.localpath(s)))
     cmd = toolpath + ' ' + args
     if _toolbool(ui, tool, "gui"):
         repo.ui.status(_('running merge tool %s for file %s\n') %
                        (tool, fcd.path()))
     repo.ui.debug('launching merge tool: %s\n' % cmd)
     r = ui.system(cmd, cwd=repo.root, environ=env, blockedtag='mergetool')
     repo.ui.debug('merge tool returned: %s\n' % r)
     return True, r, False
 
 def _formatconflictmarker(repo, ctx, template, label, pad):
     """Applies the given template to the ctx, prefixed by the label.
 
     Pad is the minimum width of the label prefix, so that multiple markers
     can have aligned templated parts.
     """
     if ctx.node() is None:
         ctx = ctx.p1()
 
     props = templatekw.keywords.copy()
     props['templ'] = template
     props['ctx'] = ctx
     props['repo'] = repo
     templateresult = template('conflictmarker', **props)
 
     label = ('%s:' % label).ljust(pad + 1)
     mark = '%s %s' % (label, templater.stringify(templateresult))
 
     if mark:
         mark = mark.splitlines()[0] # split for safety
 
     # 8 for the prefix of conflict marker lines (e.g. '<<<<<<< ')
     return util.ellipsis(mark, 80 - 8)
 
 _defaultconflictmarker = ('{node|short} '
                           '{ifeq(tags, "tip", "", '
                            'ifeq(tags, "", "", "{tags} "))}'
                           '{if(bookmarks, "{bookmarks} ")}'
                           '{ifeq(branch, "default", "", "{branch} ")}'
                           '- {author|user}: {desc|firstline}')
 
 _defaultconflictlabels = ['local', 'other']
 
 def _formatlabels(repo, fcd, fco, fca, labels):
     """Formats the given labels using the conflict marker template.
 
     Returns a list of formatted labels.
     """
     cd = fcd.changectx()
     co = fco.changectx()
     ca = fca.changectx()
 
     ui = repo.ui
     template = ui.config('ui', 'mergemarkertemplate', _defaultconflictmarker)
     tmpl = formatter.maketemplater(ui, 'conflictmarker', template)
 
     pad = max(len(l) for l in labels)
 
     newlabels = [_formatconflictmarker(repo, cd, tmpl, labels[0], pad),
                  _formatconflictmarker(repo, co, tmpl, labels[1], pad)]
     if len(labels) > 2:
         newlabels.append(_formatconflictmarker(repo, ca, tmpl, labels[2], pad))
     return newlabels
 
 def partextras(labels):
     """Return a dictionary of extra labels for use in prompts to the user
 
     Intended use is in strings of the form "(l)ocal%(l)s".
     """
     if labels is None:
         return {
             "l": "",
             "o": "",
         }
 
     return {
         "l": " [%s]" % labels[0],
         "o": " [%s]" % labels[1],
     }
 
 def _filemerge(premerge, repo, mynode, orig, fcd, fco, fca, labels=None):
     """perform a 3-way merge in the working directory
 
     premerge = whether this is a premerge
     mynode = parent node before merge
     orig = original local filename before merge
     fco = other file context
     fca = ancestor file context
     fcd = local file context for current/destination file
 
     Returns whether the merge is complete, the return value of the merge, and
     a boolean indicating whether the file was deleted from disk."""
 
     def temp(prefix, ctx):
         fullbase, ext = os.path.splitext(ctx.path())
         pre = "%s~%s." % (os.path.basename(fullbase), prefix)
         (fd, name) = tempfile.mkstemp(prefix=pre, suffix=ext)
         data = repo.wwritedata(ctx.path(), ctx.data())
         f = os.fdopen(fd, pycompat.sysstr("wb"))
         f.write(data)
         f.close()
         return name
 
     if not fco.cmp(fcd): # files identical?
         return True, None, False
 
     ui = repo.ui
     fd = fcd.path()
     binary = fcd.isbinary() or fco.isbinary() or fca.isbinary()
     symlink = 'l' in fcd.flags() + fco.flags()
     changedelete = fcd.isabsent() or fco.isabsent()
     tool, toolpath = _picktool(repo, ui, fd, binary, symlink, changedelete)
     if tool in internals and tool.startswith('internal:'):
         # normalize to new-style names (':merge' etc)
         tool = tool[len('internal'):]
     ui.debug("picked tool '%s' for %s (binary %s symlink %s changedelete %s)\n"
              % (tool, fd, binary, symlink, changedelete))
 
     if tool in internals:
         func = internals[tool]
         mergetype = func.mergetype
         onfailure = func.onfailure
         precheck = func.precheck
     else:
         func = _xmerge
         mergetype = fullmerge
         onfailure = _("merging %s failed!\n")
         precheck = None
 
     toolconf = tool, toolpath, binary, symlink
 
     if mergetype == nomerge:
         r, deleted = func(repo, mynode, orig, fcd, fco, fca, toolconf, labels)
         return True, r, deleted
 
     if premerge:
         if orig != fco.path():
             ui.status(_("merging %s and %s to %s\n") % (orig, fco.path(), fd))
         else:
             ui.status(_("merging %s\n") % fd)
 
     ui.debug("my %s other %s ancestor %s\n" % (fcd, fco, fca))
 
     if precheck and not precheck(repo, mynode, orig, fcd, fco, fca,
                                  toolconf):
         if onfailure:
             ui.warn(onfailure % fd)
         return True, 1, False
 
     a = repo.wjoin(fd)
     b = temp("base", fca)
     c = temp("other", fco)
     if not fcd.isabsent():
         back = scmutil.origpath(ui, repo, a)
         if premerge:
             util.copyfile(a, back)
     else:
         back = None
     files = (a, b, c, back)
 
     r = 1
     try:
         markerstyle = ui.config('ui', 'mergemarkers', 'basic')
         if not labels:
             labels = _defaultconflictlabels
         if markerstyle != 'basic':
             labels = _formatlabels(repo, fcd, fco, fca, labels)
 
         if premerge and mergetype == fullmerge:
             r = _premerge(repo, fcd, fco, fca, toolconf, files, labels=labels)
             # complete if premerge successful (r is 0)
             return not r, r, False
 
         needcheck, r, deleted = func(repo, mynode, orig, fcd, fco, fca,
                                      toolconf, files, labels=labels)
 
         if needcheck:
             r = _check(r, ui, tool, fcd, files)
 
         if r:
             if onfailure:
                 ui.warn(onfailure % fd)
 
         return True, r, deleted
     finally:
         if not r and back is not None:
             util.unlink(back)
         util.unlink(b)
         util.unlink(c)
 
 def _check(r, ui, tool, fcd, files):
     fd = fcd.path()
     a, b, c, back = files
 
     if not r and (_toolbool(ui, tool, "checkconflicts") or
                   'conflicts' in _toollist(ui, tool, "check")):
         if re.search("^(<<<<<<< .*|=======|>>>>>>> .*)$", fcd.data(),
                      re.MULTILINE):
             r = 1
 
     checked = False
     if 'prompt' in _toollist(ui, tool, "check"):
         checked = True
         if ui.promptchoice(_("was merge of '%s' successful (yn)?"
                              "$$ &Yes $$ &No") % fd, 1):
             r = 1
 
     if not r and not checked and (_toolbool(ui, tool, "checkchanged") or
                                   'changed' in
                                   _toollist(ui, tool, "check")):
         if back is not None and filecmp.cmp(a, back):
             if ui.promptchoice(_(" output file %s appears unchanged\n"
                                  "was merge successful (yn)?"
                                  "$$ &Yes $$ &No") % fd, 1):
                 r = 1
 
     if back is not None and _toolbool(ui, tool, "fixeol"):
         _matcheol(a, back)
 
     return r
 
 def premerge(repo, mynode, orig, fcd, fco, fca, labels=None):
     return _filemerge(True, repo, mynode, orig, fcd, fco, fca, labels=labels)
 
 def filemerge(repo, mynode, orig, fcd, fco, fca, labels=None):
     return _filemerge(False, repo, mynode, orig, fcd, fco, fca, labels=labels)
 
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = internals.values()