filemerge: add the function to examine a capability of a internal tool

For "symlink" and "binary" capabilities, _toolbool() can not examine
these of internal merge tools strictly, because it examines only
configurations in "merge-tools" section.

Users can configure them explicitly as below for example, but this is
not ordinary usage and not convenient:

  [merge-tools]
  :other.symlink = true
  :other.binary = true

This patch adds hascapability() internal function, which can examine
actual capabilities of a internal merge tool strictly.

At this patch, hascapability() is still used with "strict=False".
Subsequent patches use it with "strict=True".

mercurial/filemerge.py

@@ -1,978 +1,984
 # 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 contextlib
 import os
 import re
 import shutil
 
 from .i18n import _
 from .node import nullid, short
 
 from . import (
     encoding,
     error,
     formatter,
     match,
     pycompat,
     registrar,
     scmutil,
     simplemerge,
     tagmerge,
     templatekw,
     templater,
     util,
 )
 
 from .utils import (
     procutil,
     stringutil,
 )
 
 def _toolstr(ui, tool, part, *args):
     return ui.config("merge-tools", tool + "." + part, *args)
 
 def _toolbool(ui, tool, part,*args):
     return ui.configbool("merge-tools", tool + "." + part, *args)
 
 def _toollist(ui, tool, part):
     return ui.configlist("merge-tools", tool + "." + part)
 
 internals = {}
 # Merge tools to document.
 internalsdoc = {}
 
 internaltool = registrar.internalmerge()
 
 # internal tool merge types
 nomerge = internaltool.nomerge
 mergeonly = internaltool.mergeonly # just the full merge, no premerge
 fullmerge = internaltool.fullmerge # both premerge and merge
 
 _localchangedotherdeletedmsg = _(
     "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")
 
 _otherchangedlocaldeletedmsg = _(
     "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")
 
 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 _findtool(ui, tool):
     if tool in internals:
         return tool
     cmd = _toolstr(ui, tool, "executable", tool)
     if cmd.startswith('python:'):
         return cmd
     return findexternaltool(ui, tool)
 
 def _quotetoolpath(cmd):
     if cmd.startswith('python:'):
         return cmd
     return procutil.shellquote(cmd)
 
 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 = procutil.findexe(p + _toolstr(ui, tool, "regappend", ""))
             if p:
                 return p
     exe = _toolstr(ui, tool, "executable", tool)
     return procutil.findexe(util.expandpath(exe))
 
 def _picktool(repo, ui, path, binary, symlink, changedelete):
+    def hascapability(tool, capability, strict=False):
+        if strict and tool in internals:
+            if internals[tool].capabilities.get(capability):
+                return True
+        return _toolbool(ui, tool, capability)
+
     def supportscd(tool):
         return tool in internals and internals[tool].mergetype == nomerge
 
     def check(tool, pat, symlink, binary, changedelete):
         tmsg = tool
         if pat:
             tmsg = _("%s (for pattern %s)") % (tool, 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"):
+        elif symlink and not hascapability(tool, "symlink"):
             ui.warn(_("tool %s can't handle symlinks\n") % tmsg)
-        elif binary and not _toolbool(ui, tool, "binary"):
+        elif binary and not hascapability(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 procutil.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, _quotetoolpath(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, _quotetoolpath(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"))
         if _toolbool(ui, t, "disabled"):
             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 check(uimerge, path, symlink, binary, changedelete):
             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, _quotetoolpath(toolpath))
 
     # internal merge or prompt as last resort
     if symlink or binary or changedelete:
         if not changedelete and len(tools):
             # any tool is rejected by capability for symlink or binary
             ui.warn(_("no tool found to merge %s\n") % path)
         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, back):
     "Convert EOL markers in a file to match origfile"
     tostyle = _eoltype(back.data()) # No repo.wread filters?
     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()
 
     # Avoid prompting during an in-memory merge since it doesn't support merge
     # conflicts.
     if fcd.changectx().isinmemory():
         raise error.InMemoryMergeConflictsError('in-memory merge does not '
                                                 'support file conflicts')
 
     prompts = partextras(labels)
     prompts['fd'] = fd
     try:
         if fco.isabsent():
             index = ui.promptchoice(
                 _localchangedotherdeletedmsg % prompts, 2)
             choice = ['local', 'other', 'unresolved'][index]
         elif fcd.isabsent():
             index = ui.promptchoice(
                 _otherchangedlocaldeletedmsg % prompts, 2)
             choice = ['other', 'local', 'unresolved'][index]
         else:
             index = ui.promptchoice(
                 _("keep (l)ocal%(l)s, take (o)ther%(o)s, or leave (u)nresolved"
                   " for %(fd)s?"
                   "$$ &Local $$ &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
         _underlyingfctxifabsent(fcd).remove()
         deleted = True
     else:
         _underlyingfctxifabsent(fcd).write(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():
         _underlyingfctxifabsent(fcd).write(fco.data(), fco.flags())
     return 1, False
 
 def _underlyingfctxifabsent(filectx):
     """Sometimes when resolving, our fcd is actually an absentfilectx, but
     we want to write to it (to do the resolve). This helper returns the
     underyling workingfilectx in that case.
     """
     if filectx.isabsent():
         return filectx.changectx()[filectx.path()]
     else:
         return filectx
 
 def _premerge(repo, fcd, fco, fca, toolconf, files, labels=None):
     tool, toolpath, binary, symlink, scriptfn = toolconf
     if symlink or fcd.isabsent() or fco.isabsent():
         return 1
     unused, unused, unused, 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, fcd, fca, fco, quiet=True, label=labels)
         if not r:
             ui.debug(" premerge successful\n")
             return 0
         if premerge not in validkeep:
             # restore from backup and try again
             _restorebackup(fcd, back)
     return 1 # continue merging
 
 def _mergecheck(repo, mynode, orig, fcd, fco, fca, toolconf):
     tool, toolpath, binary, symlink, scriptfn = 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."""
     ui = repo.ui
 
     r = simplemerge.simplemerge(ui, fcd, fca, fco, 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, scriptfn = toolconf
     r = simplemerge.simplemerge(repo.ui, fcd, fca, fco, 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, binary=True, symlink=True)
 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``.
 
     This implies premerge. Therefore, files aren't dumped, if premerge
     runs successfully. Use :forcedump to forcibly write files out.
     """
     a = _workingpath(repo, fcd)
     fd = fcd.path()
 
     from . import context
     if isinstance(fcd, context.overlayworkingfilectx):
         raise error.InMemoryMergeConflictsError('in-memory merge does not '
                                                 'support the :dump tool.')
 
     util.writefile(a + ".local", fcd.decodeddata())
     repo.wwrite(fd + ".other", fco.data(), fco.flags())
     repo.wwrite(fd + ".base", fca.data(), fca.flags())
     return False, 1, False
 
 @internaltool('forcedump', mergeonly, binary=True, symlink=True)
 def _forcedump(repo, mynode, orig, fcd, fco, fca, toolconf, files,
                 labels=None):
     """
     Creates three versions of the files as same as :dump, but omits premerge.
     """
     return _idump(repo, mynode, orig, fcd, fco, fca, toolconf, files,
                 labels=labels)
 
 def _xmergeimm(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     # In-memory merge simply raises an exception on all external merge tools,
     # for now.
     #
     # It would be possible to run most tools with temporary files, but this
     # raises the question of what to do if the user only partially resolves the
     # file -- we can't leave a merge state. (Copy to somewhere in the .hg/
     # directory and tell the user how to get it is my best idea, but it's
     # clunky.)
     raise error.InMemoryMergeConflictsError('in-memory merge does not support '
                                             'external merge tools')
 
 def _xmerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels=None):
     tool, toolpath, binary, symlink, scriptfn = 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
     unused, unused, unused, back = files
     localpath = _workingpath(repo, fcd)
     args = _toolstr(repo.ui, tool, "args")
 
     with _maketempfiles(repo, fco, fca, repo.wvfs.join(back.path()),
                         "$output" in args) as temppaths:
         basepath, otherpath, localoutputpath = temppaths
         outpath = ""
         mylabel, otherlabel = labels[:2]
         if len(labels) >= 3:
             baselabel = labels[2]
         else:
             baselabel = 'base'
         env = {'HG_FILE': fcd.path(),
                'HG_MY_NODE': short(mynode),
                'HG_OTHER_NODE': short(fco.changectx().node()),
                'HG_BASE_NODE': short(fca.changectx().node()),
                'HG_MY_ISLINK': 'l' in fcd.flags(),
                'HG_OTHER_ISLINK': 'l' in fco.flags(),
                'HG_BASE_ISLINK': 'l' in fca.flags(),
                'HG_MY_LABEL': mylabel,
                'HG_OTHER_LABEL': otherlabel,
                'HG_BASE_LABEL': baselabel,
                }
         ui = repo.ui
 
         if "$output" in args:
             # read input from backup, write to original
             outpath = localpath
             localpath = localoutputpath
         replace = {'local': localpath, 'base': basepath, 'other': otherpath,
                    'output': outpath, 'labellocal': mylabel,
                    'labelother': otherlabel, 'labelbase': baselabel}
         args = util.interpolate(
             br'\$', replace, args,
             lambda s: procutil.shellquote(util.localpath(s)))
         if _toolbool(ui, tool, "gui"):
             repo.ui.status(_('running merge tool %s for file %s\n') %
                            (tool, fcd.path()))
         if scriptfn is None:
             cmd = toolpath + ' ' + args
             repo.ui.debug('launching merge tool: %s\n' % cmd)
             r = ui.system(cmd, cwd=repo.root, environ=env,
                           blockedtag='mergetool')
         else:
             repo.ui.debug('launching python merge script: %s:%s\n' %
                           (toolpath, scriptfn))
             r = 0
             try:
                 # avoid cycle cmdutil->merge->filemerge->extensions->cmdutil
                 from . import extensions
                 mod = extensions.loadpath(toolpath, 'hgmerge.%s' % tool)
             except Exception:
                 raise error.Abort(_("loading python merge script failed: %s") %
                                   toolpath)
             mergefn = getattr(mod, scriptfn, None)
             if mergefn is None:
                 raise error.Abort(_("%s does not have function: %s") %
                                   (toolpath, scriptfn))
             argslist = procutil.shellsplit(args)
             # avoid cycle cmdutil->merge->filemerge->hook->extensions->cmdutil
             from . import hook
             ret, raised = hook.pythonhook(ui, repo, "merge", toolpath,
                                           mergefn, {'args': argslist}, True)
             if raised:
                 r = 1
         repo.ui.debug('merge tool returned: %d\n' % r)
         return True, r, False
 
 def _formatconflictmarker(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 = {'ctx': ctx}
     templateresult = template.renderdefault(props)
 
     label = ('%s:' % label).ljust(pad + 1)
     mark = '%s %s' % (label, templateresult)
 
     if mark:
         mark = mark.splitlines()[0] # split for safety
 
     # 8 for the prefix of conflict marker lines (e.g. '<<<<<<< ')
     return stringutil.ellipsis(mark, 80 - 8)
 
 _defaultconflictlabels = ['local', 'other']
 
 def _formatlabels(repo, fcd, fco, fca, labels, tool=None):
     """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')
     if tool is not None:
         template = _toolstr(ui, tool, 'mergemarkertemplate', template)
     template = templater.unquotestring(template)
     tres = formatter.templateresources(ui, repo)
     tmpl = formatter.maketemplater(ui, template, defaults=templatekw.keywords,
                                    resources=tres)
 
     pad = max(len(l) for l in labels)
 
     newlabels = [_formatconflictmarker(cd, tmpl, labels[0], pad),
                  _formatconflictmarker(co, tmpl, labels[1], pad)]
     if len(labels) > 2:
         newlabels.append(_formatconflictmarker(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 _restorebackup(fcd, back):
     # TODO: Add a workingfilectx.write(otherfilectx) path so we can use
     # util.copy here instead.
     fcd.write(back.data(), fcd.flags())
 
 def _makebackup(repo, ui, wctx, fcd, premerge):
     """Makes and returns a filectx-like object for ``fcd``'s backup file.
 
     In addition to preserving the user's pre-existing modifications to `fcd`
     (if any), the backup is used to undo certain premerges, confirm whether a
     merge changed anything, and determine what line endings the new file should
     have.
 
     Backups only need to be written once (right before the premerge) since their
     content doesn't change afterwards.
     """
     if fcd.isabsent():
         return None
     # TODO: Break this import cycle somehow. (filectx -> ctx -> fileset ->
     # merge -> filemerge). (I suspect the fileset import is the weakest link)
     from . import context
     a = _workingpath(repo, fcd)
     back = scmutil.origpath(ui, repo, a)
     inworkingdir = (back.startswith(repo.wvfs.base) and not
         back.startswith(repo.vfs.base))
     if isinstance(fcd, context.overlayworkingfilectx) and inworkingdir:
         # If the backup file is to be in the working directory, and we're
         # merging in-memory, we must redirect the backup to the memory context
         # so we don't disturb the working directory.
         relpath = back[len(repo.wvfs.base) + 1:]
         if premerge:
             wctx[relpath].write(fcd.data(), fcd.flags())
         return wctx[relpath]
     else:
         if premerge:
             # Otherwise, write to wherever path the user specified the backups
             # should go. We still need to switch based on whether the source is
             # in-memory so we can use the fast path of ``util.copy`` if both are
             # on disk.
             if isinstance(fcd, context.overlayworkingfilectx):
                 util.writefile(back, fcd.data())
             else:
                 util.copyfile(a, back)
         # A arbitraryfilectx is returned, so we can run the same functions on
         # the backup context regardless of where it lives.
         return context.arbitraryfilectx(back, repo=repo)
 
 @contextlib.contextmanager
 def _maketempfiles(repo, fco, fca, localpath, uselocalpath):
     """Writes out `fco` and `fca` as temporary files, and (if uselocalpath)
     copies `localpath` to another temporary file, so an external merge tool may
     use them.
     """
     tmproot = None
     tmprootprefix = repo.ui.config('experimental', 'mergetempdirprefix')
     if tmprootprefix:
         tmproot = pycompat.mkdtemp(prefix=tmprootprefix)
 
     def maketempfrompath(prefix, path):
         fullbase, ext = os.path.splitext(path)
         pre = "%s~%s" % (os.path.basename(fullbase), prefix)
         if tmproot:
             name = os.path.join(tmproot, pre)
             if ext:
                 name += ext
             f = open(name, r"wb")
         else:
             fd, name = pycompat.mkstemp(prefix=pre + '.', suffix=ext)
             f = os.fdopen(fd, r"wb")
         return f, name
 
     def tempfromcontext(prefix, ctx):
         f, name = maketempfrompath(prefix, ctx.path())
         data = repo.wwritedata(ctx.path(), ctx.data())
         f.write(data)
         f.close()
         return name
 
     b = tempfromcontext("base", fca)
     c = tempfromcontext("other", fco)
     d = localpath
     if uselocalpath:
         # We start off with this being the backup filename, so remove the .orig
         # to make syntax-highlighting more likely.
         if d.endswith('.orig'):
             d, _ = os.path.splitext(d)
         f, d = maketempfrompath("local", d)
         with open(localpath, 'rb') as src:
             f.write(src.read())
         f.close()
 
     try:
         yield b, c, d
     finally:
         if tmproot:
             shutil.rmtree(tmproot)
         else:
             util.unlink(b)
             util.unlink(c)
             # if not uselocalpath, d is the 'orig'/backup file which we
             # shouldn't delete.
             if d and uselocalpath:
                 util.unlink(d)
 
 def _filemerge(premerge, repo, wctx, 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."""
 
     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)
     scriptfn = None
     if tool in internals and tool.startswith('internal:'):
         # normalize to new-style names (':merge' etc)
         tool = tool[len('internal'):]
     if toolpath and toolpath.startswith('python:'):
         invalidsyntax = False
         if toolpath.count(':') >= 2:
             script, scriptfn = toolpath[7:].rsplit(':', 1)
             if not scriptfn:
                 invalidsyntax = True
             # missing :callable can lead to spliting on windows drive letter
             if '\\' in scriptfn or '/' in scriptfn:
                 invalidsyntax = True
         else:
             invalidsyntax = True
         if invalidsyntax:
             raise error.Abort(_("invalid 'python:' syntax: %s") % toolpath)
         toolpath = script
     ui.debug("picked tool '%s' for %s (binary %s symlink %s changedelete %s)\n"
              % (tool, fd, pycompat.bytestr(binary), pycompat.bytestr(symlink),
                     pycompat.bytestr(changedelete)))
 
     if tool in internals:
         func = internals[tool]
         mergetype = func.mergetype
         onfailure = func.onfailure
         precheck = func.precheck
         isexternal = False
     else:
         if wctx.isinmemory():
             func = _xmergeimm
         else:
             func = _xmerge
         mergetype = fullmerge
         onfailure = _("merging %s failed!\n")
         precheck = None
         isexternal = True
 
     toolconf = tool, toolpath, binary, symlink, scriptfn
 
     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:
             if wctx.isinmemory():
                 raise error.InMemoryMergeConflictsError('in-memory merge does '
                                                         'not support merge '
                                                         'conflicts')
             ui.warn(onfailure % fd)
         return True, 1, False
 
     back = _makebackup(repo, ui, wctx, fcd, premerge)
     files = (None, None, None, back)
     r = 1
     try:
         internalmarkerstyle = ui.config('ui', 'mergemarkers')
         if isexternal:
             markerstyle = _toolstr(ui, tool, 'mergemarkers')
         else:
             markerstyle = internalmarkerstyle
 
         if not labels:
             labels = _defaultconflictlabels
         formattedlabels = labels
         if markerstyle != 'basic':
             formattedlabels = _formatlabels(repo, fcd, fco, fca, labels,
                                             tool=tool)
 
         if premerge and mergetype == fullmerge:
             # conflict markers generated by premerge will use 'detailed'
             # settings if either ui.mergemarkers or the tool's mergemarkers
             # setting is 'detailed'. This way tools can have basic labels in
             # space-constrained areas of the UI, but still get full information
             # in conflict markers if premerge is 'keep' or 'keep-merge3'.
             premergelabels = labels
             labeltool = None
             if markerstyle != 'basic':
                 # respect 'tool's mergemarkertemplate (which defaults to
                 # ui.mergemarkertemplate)
                 labeltool = tool
             if internalmarkerstyle != 'basic' or markerstyle != 'basic':
                 premergelabels = _formatlabels(repo, fcd, fco, fca,
                                                premergelabels, tool=labeltool)
 
             r = _premerge(repo, fcd, fco, fca, toolconf, files,
                           labels=premergelabels)
             # 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=formattedlabels)
 
         if needcheck:
             r = _check(repo, r, ui, tool, fcd, files)
 
         if r:
             if onfailure:
                 if wctx.isinmemory():
                     raise error.InMemoryMergeConflictsError('in-memory merge '
                                                             'does not support '
                                                             'merge conflicts')
                 ui.warn(onfailure % fd)
             _onfilemergefailure(ui)
 
         return True, r, deleted
     finally:
         if not r and back is not None:
             back.remove()
 
 def _haltmerge():
     msg = _('merge halted after failed merge (see hg resolve)')
     raise error.InterventionRequired(msg)
 
 def _onfilemergefailure(ui):
     action = ui.config('merge', 'on-failure')
     if action == 'prompt':
         msg = _('continue merge operation (yn)?' '$$ &Yes $$ &No')
         if ui.promptchoice(msg, 0) == 1:
             _haltmerge()
     if action == 'halt':
         _haltmerge()
     # default action is 'continue', in which case we neither prompt nor halt
 
 def hasconflictmarkers(data):
     return bool(re.search("^(<<<<<<< .*|=======|>>>>>>> .*)$", data,
                           re.MULTILINE))
 
 def _check(repo, r, ui, tool, fcd, files):
     fd = fcd.path()
     unused, unused, unused, back = files
 
     if not r and (_toolbool(ui, tool, "checkconflicts") or
                   'conflicts' in _toollist(ui, tool, "check")):
         if hasconflictmarkers(fcd.data()):
             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 not fcd.cmp(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(_workingpath(repo, fcd), back)
 
     return r
 
 def _workingpath(repo, ctx):
     return repo.wjoin(ctx.path())
 
 def premerge(repo, wctx, mynode, orig, fcd, fco, fca, labels=None):
     return _filemerge(True, repo, wctx, mynode, orig, fcd, fco, fca,
                       labels=labels)
 
 def filemerge(repo, wctx, mynode, orig, fcd, fco, fca, labels=None):
     return _filemerge(False, repo, wctx, mynode, orig, fcd, fco, fca,
                       labels=labels)
 
 def loadinternalmerge(ui, extname, registrarobj):
     """Load internal merge tool from specified registrarobj
     """
     for name, func in registrarobj._table.iteritems():
         fullname = ':' + name
         internals[fullname] = func
         internals['internal:' + name] = func
         internalsdoc[fullname] = func
 
 # load built-in merge tools explicitly to setup internalsdoc
 loadinternalmerge(None, None, internaltool)
 
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = internals.values()