sparse: use vfs.tryread()

vfs.exists() followed by a file read is an anti-pattern because it
incurs an extra stat() to test for file presence. vfs.tryread()
returns empty string on missing file and avoids the stat().

hgext/sparse.py

@@ -1,1128 +1,1124 b''
 # sparse.py - allow sparse checkouts of the working directory
 #
 # Copyright 2014 Facebook, Inc.
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 """allow sparse checkouts of the working directory (EXPERIMENTAL)
 
 (This extension is not yet protected by backwards compatibility
 guarantees. Any aspect may break in future releases until this
 notice is removed.)
 
 This extension allows the working directory to only consist of a
 subset of files for the revision. This allows specific files or
 directories to be explicitly included or excluded. Many repository
 operations have performance proportional to the number of files in
 the working directory. So only realizing a subset of files in the
 working directory can improve performance.
 
 Sparse Config Files
 -------------------
 
 The set of files that are part of a sparse checkout are defined by
 a sparse config file. The file defines 3 things: includes (files to
 include in the sparse checkout), excludes (files to exclude from the
 sparse checkout), and profiles (links to other config files).
 
 The file format is newline delimited. Empty lines and lines beginning
 with ``#`` are ignored.
 
 Lines beginning with ``%include `` denote another sparse config file
 to include. e.g. ``%include tests.sparse``. The filename is relative
 to the repository root.
 
 The special lines ``[include]`` and ``[exclude]`` denote the section
 for includes and excludes that follow, respectively. It is illegal to
 have ``[include]`` after ``[exclude]``. If no sections are defined,
 entries are assumed to be in the ``[include]`` section.
 
 Non-special lines resemble file patterns to be added to either includes
 or excludes. The syntax of these lines is documented by :hg:`help patterns`.
 Patterns are interpreted as ``glob:`` by default and match against the
 root of the repository.
 
 Exclusion patterns take precedence over inclusion patterns. So even
 if a file is explicitly included, an ``[exclude]`` entry can remove it.
 
 For example, say you have a repository with 3 directories, ``frontend/``,
 ``backend/``, and ``tools/``. ``frontend/`` and ``backend/`` correspond
 to different projects and it is uncommon for someone working on one
 to need the files for the other. But ``tools/`` contains files shared
 between both projects. Your sparse config files may resemble::
 
   # frontend.sparse
   frontend/**
   tools/**
 
   # backend.sparse
   backend/**
   tools/**
 
 Say the backend grows in size. Or there's a directory with thousands
 of files you wish to exclude. You can modify the profile to exclude
 certain files::
 
   [include]
   backend/**
   tools/**
 
   [exclude]
   tools/tests/**
 """
 
 from __future__ import absolute_import
 
 import collections
 import hashlib
 import os
 
 from mercurial.i18n import _
 from mercurial.node import nullid
 from mercurial import (
     cmdutil,
     commands,
     context,
     dirstate,
     error,
     extensions,
     hg,
     localrepo,
     match as matchmod,
     merge as mergemod,
     registrar,
     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'
 
 cmdtable = {}
 command = registrar.command(cmdtable)
 
 def uisetup(ui):
     _setupupdates(ui)
     _setupcommit(ui)
 
 def extsetup(ui):
     _setupclone(ui)
     _setuplog(ui)
     _setupadd(ui)
     _setupdirstate(ui)
     # if fsmonitor is enabled, tell it to use our hash function
     try:
         fsmonitor = extensions.find('fsmonitor')
         def _hashignore(orig, ignore):
             return _hashmatcher(ignore)
         extensions.wrapfunction(fsmonitor, '_hashignore', _hashignore)
     except KeyError:
         pass
 
 def reposetup(ui, repo):
     if not util.safehasattr(repo, 'dirstate'):
         return
 
     _wraprepo(ui, repo)
 
 def replacefilecache(cls, propname, replacement):
     """Replace a filecache property with a new class. This allows changing the
     cache invalidation condition."""
     origcls = cls
     assert callable(replacement)
     while cls is not object:
         if propname in cls.__dict__:
             orig = cls.__dict__[propname]
             setattr(cls, propname, replacement(orig))
             break
         cls = cls.__bases__[0]
 
     if cls is object:
         raise AttributeError(_("type '%s' has no property '%s'") % (origcls,
                              propname))
 
 def _setupupdates(ui):
     def _calculateupdates(orig, repo, wctx, mctx, ancestors, branchmerge, *arg,
                           **kwargs):
         """Filter updates to only lay out files that match the sparse rules.
         """
         actions, diverge, renamedelete = orig(repo, wctx, mctx, ancestors,
                                               branchmerge, *arg, **kwargs)
 
         if not util.safehasattr(repo, 'sparsematch'):
             return actions, diverge, renamedelete
 
         files = set()
         prunedactions = {}
         oldrevs = [pctx.rev() for pctx in wctx.parents()]
         oldsparsematch = repo.sparsematch(*oldrevs)
 
         if branchmerge:
             # If we're merging, use the wctx filter, since we're merging into
             # the wctx.
             sparsematch = repo.sparsematch(wctx.parents()[0].rev())
         else:
             # If we're updating, use the target context's filter, since we're
             # moving to the target context.
             sparsematch = repo.sparsematch(mctx.rev())
 
         temporaryfiles = []
         for file, action in actions.iteritems():
             type, args, msg = action
             files.add(file)
             if sparsematch(file):
                 prunedactions[file] = action
             elif type == 'm':
                 temporaryfiles.append(file)
                 prunedactions[file] = action
             elif branchmerge:
                 if type != 'k':
                     temporaryfiles.append(file)
                     prunedactions[file] = action
             elif type == 'f':
                 prunedactions[file] = action
             elif file in wctx:
                 prunedactions[file] = ('r', args, msg)
 
         if len(temporaryfiles) > 0:
             ui.status(_("temporarily included %d file(s) in the sparse checkout"
                 " for merging\n") % len(temporaryfiles))
             repo.addtemporaryincludes(temporaryfiles)
 
             # Add the new files to the working copy so they can be merged, etc
             actions = []
             message = 'temporarily adding to sparse checkout'
             wctxmanifest = repo[None].manifest()
             for file in temporaryfiles:
                 if file in wctxmanifest:
                     fctx = repo[None][file]
                     actions.append((file, (fctx.flags(), False), message))
 
             typeactions = collections.defaultdict(list)
             typeactions['g'] = actions
             mergemod.applyupdates(repo, typeactions, repo[None], repo['.'],
                                   False)
 
             dirstate = repo.dirstate
             for file, flags, msg in actions:
                 dirstate.normal(file)
 
         profiles = repo.getactiveprofiles()
         changedprofiles = profiles & files
         # If an active profile changed during the update, refresh the checkout.
         # Don't do this during a branch merge, since all incoming changes should
         # have been handled by the temporary includes above.
         if changedprofiles and not branchmerge:
             mf = mctx.manifest()
             for file in mf:
                 old = oldsparsematch(file)
                 new = sparsematch(file)
                 if not old and new:
                     flags = mf.flags(file)
                     prunedactions[file] = ('g', (flags, False), '')
                 elif old and not new:
                     prunedactions[file] = ('r', [], '')
 
         return prunedactions, diverge, renamedelete
 
     extensions.wrapfunction(mergemod, 'calculateupdates', _calculateupdates)
 
     def _update(orig, repo, node, branchmerge, *args, **kwargs):
         results = orig(repo, node, branchmerge, *args, **kwargs)
 
         # If we're updating to a location, clean up any stale temporary includes
         # (ex: this happens during hg rebase --abort).
         if not branchmerge and util.safehasattr(repo, 'sparsematch'):
             repo.prunetemporaryincludes()
         return results
 
     extensions.wrapfunction(mergemod, 'update', _update)
 
 def _setupcommit(ui):
     def _refreshoncommit(orig, self, node):
         """Refresh the checkout when commits touch .hgsparse
         """
         orig(self, node)
         repo = self._repo
         if util.safehasattr(repo, 'getsparsepatterns'):
             ctx = repo[node]
             _, _, profiles = repo.getsparsepatterns(ctx.rev())
             if set(profiles) & set(ctx.files()):
                 origstatus = repo.status()
                 origsparsematch = repo.sparsematch()
                 _refresh(repo.ui, repo, origstatus, origsparsematch, True)
 
             repo.prunetemporaryincludes()
 
     extensions.wrapfunction(context.committablectx, 'markcommitted',
         _refreshoncommit)
 
 def _setuplog(ui):
     entry = commands.table['^log|history']
     entry[1].append(('', 'sparse', None,
         "limit to changesets affecting the sparse checkout"))
 
     def _logrevs(orig, repo, opts):
         revs = orig(repo, opts)
         if opts.get('sparse'):
             sparsematch = repo.sparsematch()
             def ctxmatch(rev):
                 ctx = repo[rev]
                 return any(f for f in ctx.files() if sparsematch(f))
             revs = revs.filter(ctxmatch)
         return revs
     extensions.wrapfunction(cmdutil, '_logrevs', _logrevs)
 
 def _clonesparsecmd(orig, ui, repo, *args, **opts):
     include_pat = opts.get('include')
     exclude_pat = opts.get('exclude')
     enableprofile_pat = opts.get('enable_profile')
     include = exclude = enableprofile = False
     if include_pat:
         pat = include_pat
         include = True
     if exclude_pat:
         pat = exclude_pat
         exclude = True
     if enableprofile_pat:
         pat = enableprofile_pat
         enableprofile = True
     if sum([include, exclude, enableprofile]) > 1:
         raise error.Abort(_("too many flags specified."))
     if include or exclude or enableprofile:
         def clonesparse(orig, self, node, overwrite, *args, **kwargs):
             _config(self.ui, self.unfiltered(), pat, {}, include=include,
                     exclude=exclude, enableprofile=enableprofile)
             return orig(self, node, overwrite, *args, **kwargs)
         extensions.wrapfunction(hg, 'updaterepo', clonesparse)
     return orig(ui, repo, *args, **opts)
 
 def _setupclone(ui):
     entry = commands.table['^clone']
     entry[1].append(('', 'enable-profile', [],
                     'enable a sparse profile'))
     entry[1].append(('', 'include', [],
                     'include sparse pattern'))
     entry[1].append(('', 'exclude', [],
                     'exclude sparse pattern'))
     extensions.wrapcommand(commands.table, 'clone', _clonesparsecmd)
 
 def _setupadd(ui):
     entry = commands.table['^add']
     entry[1].append(('s', 'sparse', None,
                     'also include directories of added files in sparse config'))
 
     def _add(orig, ui, repo, *pats, **opts):
         if opts.get('sparse'):
             dirs = set()
             for pat in pats:
                 dirname, basename = util.split(pat)
                 dirs.add(dirname)
             _config(ui, repo, list(dirs), opts, include=True)
         return orig(ui, repo, *pats, **opts)
 
     extensions.wrapcommand(commands.table, 'add', _add)
 
 def _setupdirstate(ui):
     """Modify the dirstate to prevent stat'ing excluded files,
     and to prevent modifications to files outside the checkout.
     """
 
     def _dirstate(orig, repo):
         dirstate = orig(repo)
         dirstate.repo = repo
         return dirstate
     extensions.wrapfunction(
         localrepo.localrepository.dirstate, 'func', _dirstate)
 
     # The atrocity below is needed to wrap dirstate._ignore. It is a cached
     # property, which means normal function wrapping doesn't work.
     class ignorewrapper(object):
         def __init__(self, orig):
             self.orig = orig
             self.origignore = None
             self.func = None
             self.sparsematch = None
 
         def __get__(self, obj, type=None):
             repo = obj.repo
             origignore = self.orig.__get__(obj)
             if not util.safehasattr(repo, 'sparsematch'):
                 return origignore
 
             sparsematch = repo.sparsematch()
             if self.sparsematch != sparsematch or self.origignore != origignore:
                 self.func = unionmatcher([origignore,
                                           negatematcher(sparsematch)])
                 self.sparsematch = sparsematch
                 self.origignore = origignore
             return self.func
 
         def __set__(self, obj, value):
             return self.orig.__set__(obj, value)
 
         def __delete__(self, obj):
             return self.orig.__delete__(obj)
 
     replacefilecache(dirstate.dirstate, '_ignore', ignorewrapper)
 
     # dirstate.rebuild should not add non-matching files
     def _rebuild(orig, self, parent, allfiles, changedfiles=None):
         if util.safehasattr(self.repo, 'sparsematch'):
             matcher = self.repo.sparsematch()
             allfiles = allfiles.matches(matcher)
             if changedfiles:
                 changedfiles = [f for f in changedfiles if matcher(f)]
 
             if changedfiles is not None:
                 # In _rebuild, these files will be deleted from the dirstate
                 # when they are not found to be in allfiles
                 dirstatefilestoremove = set(f for f in self if not matcher(f))
                 changedfiles = dirstatefilestoremove.union(changedfiles)
 
         return orig(self, parent, allfiles, changedfiles)
     extensions.wrapfunction(dirstate.dirstate, 'rebuild', _rebuild)
 
     # Prevent adding files that are outside the sparse checkout
     editfuncs = ['normal', 'add', 'normallookup', 'copy', 'remove', 'merge']
     hint = _('include file with `hg debugsparse --include <pattern>` or use ' +
              '`hg add -s <file>` to include file directory while adding')
     for func in editfuncs:
         def _wrapper(orig, self, *args):
             repo = self.repo
             if util.safehasattr(repo, 'sparsematch'):
                 dirstate = repo.dirstate
                 sparsematch = repo.sparsematch()
                 for f in args:
                     if (f is not None and not sparsematch(f) and
                         f not in dirstate):
                         raise error.Abort(_("cannot add '%s' - it is outside "
                                             "the sparse checkout") % f,
                                           hint=hint)
             return orig(self, *args)
         extensions.wrapfunction(dirstate.dirstate, func, _wrapper)
 
 def _wraprepo(ui, repo):
     class SparseRepo(repo.__class__):
         def readsparseconfig(self, raw):
             """Takes a string sparse config and returns the includes,
             excludes, and profiles it specified.
             """
             includes = set()
             excludes = set()
             current = includes
             profiles = []
             for line in raw.split('\n'):
                 line = line.strip()
                 if not line or line.startswith('#'):
                     # empty or comment line, skip
                     continue
                 elif line.startswith('%include '):
                     line = line[9:].strip()
                     if line:
                         profiles.append(line)
                 elif line == '[include]':
                     if current != includes:
                         raise error.Abort(_('.hg/sparse cannot have includes ' +
                             'after excludes'))
                     continue
                 elif line == '[exclude]':
                     current = excludes
                 elif line:
                     if line.strip().startswith('/'):
                         self.ui.warn(_('warning: sparse profile cannot use' +
                                        ' paths starting with /, ignoring %s\n')
                                        % line)
                         continue
                     current.add(line)
 
             return includes, excludes, profiles
 
         def getsparsepatterns(self, rev):
             """Returns the include/exclude patterns specified by the
             given rev.
             """
-            if not self.vfs.exists('sparse'):
+            raw = self.vfs.tryread('sparse')
+            if not raw:
                 return set(), set(), []
             if rev is None:
                 raise error.Abort(_("cannot parse sparse patterns from " +
                     "working copy"))
 
-            raw = self.vfs.read('sparse')
             includes, excludes, profiles = self.readsparseconfig(raw)
 
             ctx = self[rev]
             if profiles:
                 visited = set()
                 while profiles:
                     profile = profiles.pop()
                     if profile in visited:
                         continue
                     visited.add(profile)
 
                     try:
                         raw = self.getrawprofile(profile, rev)
                     except error.ManifestLookupError:
                         msg = (
                             "warning: sparse profile '%s' not found "
                             "in rev %s - ignoring it\n" % (profile, ctx))
                         if self.ui.configbool(
                                 'sparse', 'missingwarning', True):
                             self.ui.warn(msg)
                         else:
                             self.ui.debug(msg)
                         continue
                     pincludes, pexcludes, subprofs = \
                         self.readsparseconfig(raw)
                     includes.update(pincludes)
                     excludes.update(pexcludes)
                     for subprofile in subprofs:
                         profiles.append(subprofile)
 
                 profiles = visited
 
             if includes:
                 includes.add('.hg*')
             return includes, excludes, profiles
 
         def getrawprofile(self, profile, changeid):
             # TODO add some kind of cache here because this incurs a manifest
             # resolve and can be slow.
             return self.filectx(profile, changeid=changeid).data()
 
         def _sparsechecksum(self, path):
             data = self.vfs.read(path)
             return hashlib.sha1(data).hexdigest()
 
         def _sparsesignature(self, includetemp=True):
             """Returns the signature string representing the contents of the
             current project sparse configuration. This can be used to cache the
             sparse matcher for a given set of revs."""
             signaturecache = self.signaturecache
             signature = signaturecache.get('signature')
             if includetemp:
                 tempsignature = signaturecache.get('tempsignature')
             else:
                 tempsignature = 0
 
             if signature is None or (includetemp and tempsignature is None):
                 signature = 0
                 try:
                     signature = self._sparsechecksum('sparse')
                 except (OSError, IOError):
                     pass
                 signaturecache['signature'] = signature
 
                 tempsignature = 0
                 if includetemp:
                     try:
                         tempsignature = self._sparsechecksum('tempsparse')
                     except (OSError, IOError):
                         pass
                     signaturecache['tempsignature'] = tempsignature
             return '%s %s' % (str(signature), str(tempsignature))
 
         def invalidatecaches(self):
             self.invalidatesignaturecache()
             return super(SparseRepo, self).invalidatecaches()
 
         def invalidatesignaturecache(self):
             self.signaturecache.clear()
 
         def sparsematch(self, *revs, **kwargs):
             """Returns the sparse match function for the given revs.
 
             If multiple revs are specified, the match function is the union
             of all the revs.
 
             `includetemp` is used to indicate if the temporarily included file
             should be part of the matcher.
             """
             if not revs or revs == (None,):
                 revs = [self.changelog.rev(node) for node in
                     self.dirstate.parents() if node != nullid]
 
             includetemp = kwargs.get('includetemp', True)
             signature = self._sparsesignature(includetemp=includetemp)
 
             key = '%s %s' % (str(signature), ' '.join([str(r) for r in revs]))
 
             result = self.sparsecache.get(key, None)
             if result:
                 return result
 
             matchers = []
             for rev in revs:
                 try:
                     includes, excludes, profiles = self.getsparsepatterns(rev)
 
                     if includes or excludes:
                         # Explicitly include subdirectories of includes so
                         # status will walk them down to the actual include.
                         subdirs = set()
                         for include in includes:
                             dirname = os.path.dirname(include)
                             # basename is used to avoid issues with absolute
                             # paths (which on Windows can include the drive).
                             while os.path.basename(dirname):
                                 subdirs.add(dirname)
                                 dirname = os.path.dirname(dirname)
 
                         matcher = matchmod.match(self.root, '', [],
                             include=includes, exclude=excludes,
                             default='relpath')
                         if subdirs:
                             matcher = forceincludematcher(matcher, subdirs)
                         matchers.append(matcher)
                 except IOError:
                     pass
 
             result = None
             if not matchers:
                 result = matchmod.always(self.root, '')
             elif len(matchers) == 1:
                 result = matchers[0]
             else:
                 result = unionmatcher(matchers)
 
             if kwargs.get('includetemp', True):
                 tempincludes = self.gettemporaryincludes()
                 result = forceincludematcher(result, tempincludes)
 
             self.sparsecache[key] = result
 
             return result
 
         def getactiveprofiles(self):
             revs = [self.changelog.rev(node) for node in
                     self.dirstate.parents() if node != nullid]
 
             activeprofiles = set()
             for rev in revs:
                 _, _, profiles = self.getsparsepatterns(rev)
                 activeprofiles.update(profiles)
 
             return activeprofiles
 
         def writesparseconfig(self, include, exclude, profiles):
             raw = '%s[include]\n%s\n[exclude]\n%s\n' % (
                 ''.join(['%%include %s\n' % p for p in sorted(profiles)]),
                 '\n'.join(sorted(include)),
                 '\n'.join(sorted(exclude)))
             self.vfs.write("sparse", raw)
             self.invalidatesignaturecache()
 
         def addtemporaryincludes(self, files):
             includes = self.gettemporaryincludes()
             for file in files:
                 includes.add(file)
             self._writetemporaryincludes(includes)
 
         def gettemporaryincludes(self):
             existingtemp = set()
-            if self.vfs.exists('tempsparse'):
-                raw = self.vfs.read('tempsparse')
+            raw = self.vfs.tryread('tempsparse')
+            if raw:
                 existingtemp.update(raw.split('\n'))
             return existingtemp
 
         def _writetemporaryincludes(self, includes):
             raw = '\n'.join(sorted(includes))
             self.vfs.write('tempsparse', raw)
             self.invalidatesignaturecache()
 
         def prunetemporaryincludes(self):
             if repo.vfs.exists('tempsparse'):
                 origstatus = self.status()
                 modified, added, removed, deleted, a, b, c = origstatus
                 if modified or added or removed or deleted:
                     # Still have pending changes. Don't bother trying to prune.
                     return
 
                 sparsematch = self.sparsematch(includetemp=False)
                 dirstate = self.dirstate
                 actions = []
                 dropped = []
                 tempincludes = self.gettemporaryincludes()
                 for file in tempincludes:
                     if file in dirstate and not sparsematch(file):
                         message = 'dropping temporarily included sparse files'
                         actions.append((file, None, message))
                         dropped.append(file)
 
                 typeactions = collections.defaultdict(list)
                 typeactions['r'] = actions
                 mergemod.applyupdates(self, typeactions, self[None], self['.'],
                                       False)
 
                 # Fix dirstate
                 for file in dropped:
                     dirstate.drop(file)
 
                 self.vfs.unlink('tempsparse')
                 self.invalidatesignaturecache()
                 msg = _("cleaned up %d temporarily added file(s) from the "
                         "sparse checkout\n")
                 ui.status(msg % len(tempincludes))
 
     if 'dirstate' in repo._filecache:
         repo.dirstate.repo = repo
     repo.sparsecache = {}
     repo.signaturecache = {}
     repo.__class__ = SparseRepo
 
 @command('^debugsparse', [
     ('I', 'include', False, _('include files in the sparse checkout')),
     ('X', 'exclude', False, _('exclude files in the sparse checkout')),
     ('d', 'delete', False, _('delete an include/exclude rule')),
     ('f', 'force', False, _('allow changing rules even with pending changes')),
     ('', 'enable-profile', False, _('enables the specified profile')),
     ('', 'disable-profile', False, _('disables the specified profile')),
     ('', 'import-rules', False, _('imports rules from a file')),
     ('', 'clear-rules', False, _('clears local include/exclude rules')),
     ('', 'refresh', False, _('updates the working after sparseness changes')),
     ('', 'reset', False, _('makes the repo full again')),
     ] + commands.templateopts,
     _('[--OPTION] PATTERN...'))
 def debugsparse(ui, repo, *pats, **opts):
     """make the current checkout sparse, or edit the existing checkout
 
     The sparse command is used to make the current checkout sparse.
     This means files that don't meet the sparse condition will not be
     written to disk, or show up in any working copy operations. It does
     not affect files in history in any way.
 
     Passing no arguments prints the currently applied sparse rules.
 
     --include and --exclude are used to add and remove files from the sparse
     checkout. The effects of adding an include or exclude rule are applied
     immediately. If applying the new rule would cause a file with pending
     changes to be added or removed, the command will fail. Pass --force to
     force a rule change even with pending changes (the changes on disk will
     be preserved).
 
     --delete removes an existing include/exclude rule. The effects are
     immediate.
 
     --refresh refreshes the files on disk based on the sparse rules. This is
     only necessary if .hg/sparse was changed by hand.
 
     --enable-profile and --disable-profile accept a path to a .hgsparse file.
     This allows defining sparse checkouts and tracking them inside the
     repository. This is useful for defining commonly used sparse checkouts for
     many people to use. As the profile definition changes over time, the sparse
     checkout will automatically be updated appropriately, depending on which
     changeset is checked out. Changes to .hgsparse are not applied until they
     have been committed.
 
     --import-rules accepts a path to a file containing rules in the .hgsparse
     format, allowing you to add --include, --exclude and --enable-profile rules
     in bulk. Like the --include, --exclude and --enable-profile switches, the
     changes are applied immediately.
 
     --clear-rules removes all local include and exclude rules, while leaving
     any enabled profiles in place.
 
     Returns 0 if editing the sparse checkout succeeds.
     """
     include = opts.get('include')
     exclude = opts.get('exclude')
     force = opts.get('force')
     enableprofile = opts.get('enable_profile')
     disableprofile = opts.get('disable_profile')
     importrules = opts.get('import_rules')
     clearrules = opts.get('clear_rules')
     delete = opts.get('delete')
     refresh = opts.get('refresh')
     reset = opts.get('reset')
     count = sum([include, exclude, enableprofile, disableprofile, delete,
                  importrules, refresh, clearrules, reset])
     if count > 1:
         raise error.Abort(_("too many flags specified"))
 
     if count == 0:
         if repo.vfs.exists('sparse'):
             ui.status(repo.vfs.read("sparse") + "\n")
             temporaryincludes = repo.gettemporaryincludes()
             if temporaryincludes:
                 ui.status(_("Temporarily Included Files (for merge/rebase):\n"))
                 ui.status(("\n".join(temporaryincludes) + "\n"))
         else:
             ui.status(_('repo is not sparse\n'))
         return
 
     if include or exclude or delete or reset or enableprofile or disableprofile:
         _config(ui, repo, pats, opts, include=include, exclude=exclude,
                 reset=reset, delete=delete, enableprofile=enableprofile,
                 disableprofile=disableprofile, force=force)
 
     if importrules:
         _import(ui, repo, pats, opts, force=force)
 
     if clearrules:
         _clear(ui, repo, pats, force=force)
 
     if refresh:
         try:
             wlock = repo.wlock()
             fcounts = map(
                 len,
                 _refresh(ui, repo, repo.status(), repo.sparsematch(), force))
             _verbose_output(ui, opts, 0, 0, 0, *fcounts)
         finally:
             wlock.release()
 
 def _config(ui, repo, pats, opts, include=False, exclude=False, reset=False,
             delete=False, enableprofile=False, disableprofile=False,
             force=False):
     """
     Perform a sparse config update. Only one of the kwargs may be specified.
     """
     wlock = repo.wlock()
     try:
         oldsparsematch = repo.sparsematch()
 
-        if repo.vfs.exists('sparse'):
-            raw = repo.vfs.read('sparse')
+        raw = repo.vfs.tryread('sparse')
+        if raw:
             oldinclude, oldexclude, oldprofiles = map(
                 set, repo.readsparseconfig(raw))
         else:
             oldinclude = set()
             oldexclude = set()
             oldprofiles = set()
 
         try:
             if reset:
                 newinclude = set()
                 newexclude = set()
                 newprofiles = set()
             else:
                 newinclude = set(oldinclude)
                 newexclude = set(oldexclude)
                 newprofiles = set(oldprofiles)
 
             oldstatus = repo.status()
 
             if any(pat.startswith('/') for pat in pats):
                 ui.warn(_('warning: paths cannot start with /, ignoring: %s\n')
                           % ([pat for pat in pats if pat.startswith('/')]))
             elif include:
                 newinclude.update(pats)
             elif exclude:
                 newexclude.update(pats)
             elif enableprofile:
                 newprofiles.update(pats)
             elif disableprofile:
                 newprofiles.difference_update(pats)
             elif delete:
                 newinclude.difference_update(pats)
                 newexclude.difference_update(pats)
 
             repo.writesparseconfig(newinclude, newexclude, newprofiles)
             fcounts = map(
                 len, _refresh(ui, repo, oldstatus, oldsparsematch, force))
 
             profilecount = (len(newprofiles - oldprofiles) -
                             len(oldprofiles - newprofiles))
             includecount = (len(newinclude - oldinclude) -
                             len(oldinclude - newinclude))
             excludecount = (len(newexclude - oldexclude) -
                             len(oldexclude - newexclude))
             _verbose_output(
                 ui, opts, profilecount, includecount, excludecount, *fcounts)
         except Exception:
             repo.writesparseconfig(oldinclude, oldexclude, oldprofiles)
             raise
     finally:
         wlock.release()
 
 def _import(ui, repo, files, opts, force=False):
     with repo.wlock():
         # load union of current active profile
         revs = [repo.changelog.rev(node) for node in
                 repo.dirstate.parents() if node != nullid]
 
         # read current configuration
-        raw = ''
-        if repo.vfs.exists('sparse'):
-            raw = repo.vfs.read('sparse')
+        raw = repo.vfs.tryread('sparse')
         oincludes, oexcludes, oprofiles = repo.readsparseconfig(raw)
         includes, excludes, profiles = map(
                 set, (oincludes, oexcludes, oprofiles))
 
         # all active rules
         aincludes, aexcludes, aprofiles = set(), set(), set()
         for rev in revs:
             rincludes, rexcludes, rprofiles = repo.getsparsepatterns(rev)
             aincludes.update(rincludes)
             aexcludes.update(rexcludes)
             aprofiles.update(rprofiles)
 
         # import rules on top; only take in rules that are not yet
         # part of the active rules.
         changed = False
         for file in files:
             with util.posixfile(util.expandpath(file)) as importfile:
                 iincludes, iexcludes, iprofiles = repo.readsparseconfig(
                     importfile.read())
                 oldsize = len(includes) + len(excludes) + len(profiles)
                 includes.update(iincludes - aincludes)
                 excludes.update(iexcludes - aexcludes)
                 profiles.update(set(iprofiles) - aprofiles)
                 if len(includes) + len(excludes) + len(profiles) > oldsize:
                     changed = True
 
         profilecount = includecount = excludecount = 0
         fcounts = (0, 0, 0)
 
         if changed:
             profilecount = len(profiles - aprofiles)
             includecount = len(includes - aincludes)
             excludecount = len(excludes - aexcludes)
 
             oldstatus = repo.status()
             oldsparsematch = repo.sparsematch()
             repo.writesparseconfig(includes, excludes, profiles)
 
             try:
                 fcounts = map(
                     len, _refresh(ui, repo, oldstatus, oldsparsematch, force))
             except Exception:
                 repo.writesparseconfig(oincludes, oexcludes, oprofiles)
                 raise
 
         _verbose_output(ui, opts, profilecount, includecount, excludecount,
                         *fcounts)
 
 def _clear(ui, repo, files, force=False):
     with repo.wlock():
-        raw = ''
-        if repo.vfs.exists('sparse'):
-            raw = repo.vfs.read('sparse')
+        raw = repo.vfs.tryread('sparse')
         includes, excludes, profiles = repo.readsparseconfig(raw)
 
         if includes or excludes:
             oldstatus = repo.status()
             oldsparsematch = repo.sparsematch()
             repo.writesparseconfig(set(), set(), profiles)
             _refresh(ui, repo, oldstatus, oldsparsematch, force)
 
 def _refresh(ui, repo, origstatus, origsparsematch, force):
     """Refreshes which files are on disk by comparing the old status and
     sparsematch with the new sparsematch.
 
     Will raise an exception if a file with pending changes is being excluded
     or included (unless force=True).
     """
     modified, added, removed, deleted, unknown, ignored, clean = origstatus
 
     # Verify there are no pending changes
     pending = set()
     pending.update(modified)
     pending.update(added)
     pending.update(removed)
     sparsematch = repo.sparsematch()
     abort = False
     for file in pending:
         if not sparsematch(file):
             ui.warn(_("pending changes to '%s'\n") % file)
             abort = not force
     if abort:
         raise error.Abort(_("could not update sparseness due to " +
             "pending changes"))
 
     # Calculate actions
     dirstate = repo.dirstate
     ctx = repo['.']
     added = []
     lookup = []
     dropped = []
     mf = ctx.manifest()
     files = set(mf)
 
     actions = {}
 
     for file in files:
         old = origsparsematch(file)
         new = sparsematch(file)
         # Add files that are newly included, or that don't exist in
         # the dirstate yet.
         if (new and not old) or (old and new and not file in dirstate):
             fl = mf.flags(file)
             if repo.wvfs.exists(file):
                 actions[file] = ('e', (fl,), '')
                 lookup.append(file)
             else:
                 actions[file] = ('g', (fl, False), '')
                 added.append(file)
         # Drop files that are newly excluded, or that still exist in
         # the dirstate.
         elif (old and not new) or (not old and not new and file in dirstate):
             dropped.append(file)
             if file not in pending:
                 actions[file] = ('r', [], '')
 
     # Verify there are no pending changes in newly included files
     abort = False
     for file in lookup:
         ui.warn(_("pending changes to '%s'\n") % file)
         abort = not force
     if abort:
         raise error.Abort(_("cannot change sparseness due to " +
             "pending changes (delete the files or use --force " +
             "to bring them back dirty)"))
 
     # Check for files that were only in the dirstate.
     for file, state in dirstate.iteritems():
         if not file in files:
             old = origsparsematch(file)
             new = sparsematch(file)
             if old and not new:
                 dropped.append(file)
 
     # Apply changes to disk
     typeactions = dict((m, []) for m in 'a f g am cd dc r dm dg m e k'.split())
     for f, (m, args, msg) in actions.iteritems():
         if m not in typeactions:
             typeactions[m] = []
         typeactions[m].append((f, args, msg))
     mergemod.applyupdates(repo, typeactions, repo[None], repo['.'], False)
 
     # Fix dirstate
     for file in added:
         dirstate.normal(file)
 
     for file in dropped:
         dirstate.drop(file)
 
     for file in lookup:
         # File exists on disk, and we're bringing it back in an unknown state.
         dirstate.normallookup(file)
 
     return added, dropped, lookup
 
 def _verbose_output(ui, opts, profilecount, includecount, excludecount, added,
                     dropped, lookup):
     """Produce --verbose and templatable output
 
     This specifically enables -Tjson, providing machine-readable stats on how
     the sparse profile changed.
 
     """
     with ui.formatter('sparse', opts) as fm:
         fm.startitem()
         fm.condwrite(ui.verbose, 'profiles_added', 'Profile # change: %d\n',
                      profilecount)
         fm.condwrite(ui.verbose, 'include_rules_added',
                      'Include rule # change: %d\n', includecount)
         fm.condwrite(ui.verbose, 'exclude_rules_added',
                      'Exclude rule # change: %d\n', excludecount)
         # In 'plain' verbose mode, mergemod.applyupdates already outputs what
         # files are added or removed outside of the templating formatter
         # framework. No point in repeating ourselves in that case.
         if not fm.isplain():
             fm.condwrite(ui.verbose, 'files_added', 'Files added: %d\n',
                          added)
             fm.condwrite(ui.verbose, 'files_dropped', 'Files dropped: %d\n',
                          dropped)
             fm.condwrite(ui.verbose, 'files_conflicting',
                          'Files conflicting: %d\n', lookup)
 
 class forceincludematcher(object):
     """A matcher that returns true for any of the forced includes before testing
     against the actual matcher."""
     def __init__(self, matcher, includes):
         self._matcher = matcher
         self._includes = includes
 
     def __call__(self, value):
         return value in self._includes or self._matcher(value)
 
     def always(self):
         return False
 
     def files(self):
         return []
 
     def isexact(self):
         return False
 
     def anypats(self):
         return True
 
     def prefix(self):
         return False
 
     def hash(self):
         sha1 = hashlib.sha1()
         sha1.update(_hashmatcher(self._matcher))
         for include in sorted(self._includes):
             sha1.update(include + '\0')
         return sha1.hexdigest()
 
 class unionmatcher(object):
     """A matcher that is the union of several matchers."""
     def __init__(self, matchers):
         self._matchers = matchers
 
     def __call__(self, value):
         for match in self._matchers:
             if match(value):
                 return True
         return False
 
     def always(self):
         return False
 
     def files(self):
         return []
 
     def isexact(self):
         return False
 
     def anypats(self):
         return True
 
     def prefix(self):
         return False
 
     def hash(self):
         sha1 = hashlib.sha1()
         for m in self._matchers:
             sha1.update(_hashmatcher(m))
         return sha1.hexdigest()
 
 class negatematcher(object):
     def __init__(self, matcher):
         self._matcher = matcher
 
     def __call__(self, value):
         return not self._matcher(value)
 
     def always(self):
         return False
 
     def files(self):
         return []
 
     def isexact(self):
         return False
 
     def anypats(self):
         return True
 
     def hash(self):
         sha1 = hashlib.sha1()
         sha1.update('negate')
         sha1.update(_hashmatcher(self._matcher))
         return sha1.hexdigest()
 
 def _hashmatcher(matcher):
     if util.safehasattr(matcher, 'hash'):
         return matcher.hash()
 
     sha1 = hashlib.sha1()
     sha1.update(repr(matcher))
     return sha1.hexdigest()