lfutil: provide a hint if the largefiles/lfs cache path cannot be determined

A coworker hit this error using an LFS repo in a stripped down environment, and
didn't know how to resolve it.

The final conditional is a bit fast and loose, but there is currently no 'posix'
test in hghave, and it doesn't seem like it's worth adding for this since I
think Windows is the only non-POSIX platform we run tests on.

Differential Revision: https://phab.mercurial-scm.org/D8145

hgext/largefiles/lfutil.py

@@ -1,760 +1,781 b''
 # Copyright 2009-2010 Gregory P. Ward
 # Copyright 2009-2010 Intelerad Medical Systems Incorporated
 # Copyright 2010-2011 Fog Creek Software
 # Copyright 2010-2011 Unity Technologies
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 '''largefiles utility code: must not import other modules in this package.'''
 from __future__ import absolute_import
 
 import contextlib
 import copy
 import os
 import stat
 
 from mercurial.i18n import _
 from mercurial.node import hex
 from mercurial.pycompat import open
 
 from mercurial import (
     dirstate,
     encoding,
     error,
     httpconnection,
     match as matchmod,
     node,
     pycompat,
     scmutil,
     sparse,
     util,
     vfs as vfsmod,
 )
 from mercurial.utils import hashutil
 
 shortname = b'.hglf'
 shortnameslash = shortname + b'/'
 longname = b'largefiles'
 
 # -- Private worker functions ------------------------------------------
 
 
 @contextlib.contextmanager
 def lfstatus(repo, value=True):
     oldvalue = getattr(repo, 'lfstatus', False)
     repo.lfstatus = value
     try:
         yield
     finally:
         repo.lfstatus = oldvalue
 
 
 def getminsize(ui, assumelfiles, opt, default=10):
     lfsize = opt
     if not lfsize and assumelfiles:
         lfsize = ui.config(longname, b'minsize', default=default)
     if lfsize:
         try:
             lfsize = float(lfsize)
         except ValueError:
             raise error.Abort(
                 _(b'largefiles: size must be number (not %s)\n') % lfsize
             )
     if lfsize is None:
         raise error.Abort(_(b'minimum size for largefiles must be specified'))
     return lfsize
 
 
 def link(src, dest):
     """Try to create hardlink - if that fails, efficiently make a copy."""
     util.makedirs(os.path.dirname(dest))
     try:
         util.oslink(src, dest)
     except OSError:
         # if hardlinks fail, fallback on atomic copy
         with open(src, b'rb') as srcf, util.atomictempfile(dest) as dstf:
             for chunk in util.filechunkiter(srcf):
                 dstf.write(chunk)
         os.chmod(dest, os.stat(src).st_mode)
 
 
 def usercachepath(ui, hash):
     '''Return the correct location in the "global" largefiles cache for a file
     with the given hash.
     This cache is used for sharing of largefiles across repositories - both
     to preserve download bandwidth and storage space.'''
     return os.path.join(_usercachedir(ui), hash)
 
 
 def _usercachedir(ui, name=longname):
     '''Return the location of the "global" largefiles cache.'''
     path = ui.configpath(name, b'usercache')
     if path:
         return path
+
+    hint = None
+
     if pycompat.iswindows:
         appdata = encoding.environ.get(
             b'LOCALAPPDATA', encoding.environ.get(b'APPDATA')
         )
         if appdata:
             return os.path.join(appdata, name)
+
+        hint = _(b"define %s or %s in the environment, or set %s.usercache") % (
+            b"LOCALAPPDATA",
+            b"APPDATA",
+            name,
+        )
     elif pycompat.isdarwin:
         home = encoding.environ.get(b'HOME')
         if home:
             return os.path.join(home, b'Library', b'Caches', name)
+
+        hint = _(b"define %s in the environment, or set %s.usercache") % (
+            b"HOME",
+            name,
+        )
     elif pycompat.isposix:
         path = encoding.environ.get(b'XDG_CACHE_HOME')
         if path:
             return os.path.join(path, name)
         home = encoding.environ.get(b'HOME')
         if home:
             return os.path.join(home, b'.cache', name)
+
+        hint = _(b"define %s or %s in the environment, or set %s.usercache") % (
+            b"XDG_CACHE_HOME",
+            b"HOME",
+            name,
+        )
     else:
         raise error.Abort(
             _(b'unknown operating system: %s\n') % pycompat.osname
         )
-    raise error.Abort(_(b'unknown %s usercache location') % name)
+
+    raise error.Abort(_(b'unknown %s usercache location') % name, hint=hint)
 
 
 def inusercache(ui, hash):
     path = usercachepath(ui, hash)
     return os.path.exists(path)
 
 
 def findfile(repo, hash):
     '''Return store path of the largefile with the specified hash.
     As a side effect, the file might be linked from user cache.
     Return None if the file can't be found locally.'''
     path, exists = findstorepath(repo, hash)
     if exists:
         repo.ui.note(_(b'found %s in store\n') % hash)
         return path
     elif inusercache(repo.ui, hash):
         repo.ui.note(_(b'found %s in system cache\n') % hash)
         path = storepath(repo, hash)
         link(usercachepath(repo.ui, hash), path)
         return path
     return None
 
 
 class largefilesdirstate(dirstate.dirstate):
     def __getitem__(self, key):
         return super(largefilesdirstate, self).__getitem__(unixpath(key))
 
     def normal(self, f):
         return super(largefilesdirstate, self).normal(unixpath(f))
 
     def remove(self, f):
         return super(largefilesdirstate, self).remove(unixpath(f))
 
     def add(self, f):
         return super(largefilesdirstate, self).add(unixpath(f))
 
     def drop(self, f):
         return super(largefilesdirstate, self).drop(unixpath(f))
 
     def forget(self, f):
         return super(largefilesdirstate, self).forget(unixpath(f))
 
     def normallookup(self, f):
         return super(largefilesdirstate, self).normallookup(unixpath(f))
 
     def _ignore(self, f):
         return False
 
     def write(self, tr=False):
         # (1) disable PENDING mode always
         #     (lfdirstate isn't yet managed as a part of the transaction)
         # (2) avoid develwarn 'use dirstate.write with ....'
         super(largefilesdirstate, self).write(None)
 
 
 def openlfdirstate(ui, repo, create=True):
     '''
     Return a dirstate object that tracks largefiles: i.e. its root is
     the repo root, but it is saved in .hg/largefiles/dirstate.
     '''
     vfs = repo.vfs
     lfstoredir = longname
     opener = vfsmod.vfs(vfs.join(lfstoredir))
     lfdirstate = largefilesdirstate(
         opener,
         ui,
         repo.root,
         repo.dirstate._validate,
         lambda: sparse.matcher(repo),
     )
 
     # If the largefiles dirstate does not exist, populate and create
     # it. This ensures that we create it on the first meaningful
     # largefiles operation in a new clone.
     if create and not vfs.exists(vfs.join(lfstoredir, b'dirstate')):
         matcher = getstandinmatcher(repo)
         standins = repo.dirstate.walk(
             matcher, subrepos=[], unknown=False, ignored=False
         )
 
         if len(standins) > 0:
             vfs.makedirs(lfstoredir)
 
         for standin in standins:
             lfile = splitstandin(standin)
             lfdirstate.normallookup(lfile)
     return lfdirstate
 
 
 def lfdirstatestatus(lfdirstate, repo):
     pctx = repo[b'.']
     match = matchmod.always()
     unsure, s = lfdirstate.status(
         match, subrepos=[], ignored=False, clean=False, unknown=False
     )
     modified, clean = s.modified, s.clean
     for lfile in unsure:
         try:
             fctx = pctx[standin(lfile)]
         except LookupError:
             fctx = None
         if not fctx or readasstandin(fctx) != hashfile(repo.wjoin(lfile)):
             modified.append(lfile)
         else:
             clean.append(lfile)
             lfdirstate.normal(lfile)
     return s
 
 
 def listlfiles(repo, rev=None, matcher=None):
     '''return a list of largefiles in the working copy or the
     specified changeset'''
 
     if matcher is None:
         matcher = getstandinmatcher(repo)
 
     # ignore unknown files in working directory
     return [
         splitstandin(f)
         for f in repo[rev].walk(matcher)
         if rev is not None or repo.dirstate[f] != b'?'
     ]
 
 
 def instore(repo, hash, forcelocal=False):
     '''Return true if a largefile with the given hash exists in the store'''
     return os.path.exists(storepath(repo, hash, forcelocal))
 
 
 def storepath(repo, hash, forcelocal=False):
     '''Return the correct location in the repository largefiles store for a
     file with the given hash.'''
     if not forcelocal and repo.shared():
         return repo.vfs.reljoin(repo.sharedpath, longname, hash)
     return repo.vfs.join(longname, hash)
 
 
 def findstorepath(repo, hash):
     '''Search through the local store path(s) to find the file for the given
     hash.  If the file is not found, its path in the primary store is returned.
     The return value is a tuple of (path, exists(path)).
     '''
     # For shared repos, the primary store is in the share source.  But for
     # backward compatibility, force a lookup in the local store if it wasn't
     # found in the share source.
     path = storepath(repo, hash, False)
 
     if instore(repo, hash):
         return (path, True)
     elif repo.shared() and instore(repo, hash, True):
         return storepath(repo, hash, True), True
 
     return (path, False)
 
 
 def copyfromcache(repo, hash, filename):
     '''Copy the specified largefile from the repo or system cache to
     filename in the repository. Return true on success or false if the
     file was not found in either cache (which should not happened:
     this is meant to be called only after ensuring that the needed
     largefile exists in the cache).'''
     wvfs = repo.wvfs
     path = findfile(repo, hash)
     if path is None:
         return False
     wvfs.makedirs(wvfs.dirname(wvfs.join(filename)))
     # The write may fail before the file is fully written, but we
     # don't use atomic writes in the working copy.
     with open(path, b'rb') as srcfd, wvfs(filename, b'wb') as destfd:
         gothash = copyandhash(util.filechunkiter(srcfd), destfd)
     if gothash != hash:
         repo.ui.warn(
             _(b'%s: data corruption in %s with hash %s\n')
             % (filename, path, gothash)
         )
         wvfs.unlink(filename)
         return False
     return True
 
 
 def copytostore(repo, ctx, file, fstandin):
     wvfs = repo.wvfs
     hash = readasstandin(ctx[fstandin])
     if instore(repo, hash):
         return
     if wvfs.exists(file):
         copytostoreabsolute(repo, wvfs.join(file), hash)
     else:
         repo.ui.warn(
             _(b"%s: largefile %s not available from local store\n")
             % (file, hash)
         )
 
 
 def copyalltostore(repo, node):
     '''Copy all largefiles in a given revision to the store'''
 
     ctx = repo[node]
     for filename in ctx.files():
         realfile = splitstandin(filename)
         if realfile is not None and filename in ctx.manifest():
             copytostore(repo, ctx, realfile, filename)
 
 
 def copytostoreabsolute(repo, file, hash):
     if inusercache(repo.ui, hash):
         link(usercachepath(repo.ui, hash), storepath(repo, hash))
     else:
         util.makedirs(os.path.dirname(storepath(repo, hash)))
         with open(file, b'rb') as srcf:
             with util.atomictempfile(
                 storepath(repo, hash), createmode=repo.store.createmode
             ) as dstf:
                 for chunk in util.filechunkiter(srcf):
                     dstf.write(chunk)
         linktousercache(repo, hash)
 
 
 def linktousercache(repo, hash):
     '''Link / copy the largefile with the specified hash from the store
     to the cache.'''
     path = usercachepath(repo.ui, hash)
     link(storepath(repo, hash), path)
 
 
 def getstandinmatcher(repo, rmatcher=None):
     '''Return a match object that applies rmatcher to the standin directory'''
     wvfs = repo.wvfs
     standindir = shortname
 
     # no warnings about missing files or directories
     badfn = lambda f, msg: None
 
     if rmatcher and not rmatcher.always():
         pats = [wvfs.join(standindir, pat) for pat in rmatcher.files()]
         if not pats:
             pats = [wvfs.join(standindir)]
         match = scmutil.match(repo[None], pats, badfn=badfn)
     else:
         # no patterns: relative to repo root
         match = scmutil.match(repo[None], [wvfs.join(standindir)], badfn=badfn)
     return match
 
 
 def composestandinmatcher(repo, rmatcher):
     '''Return a matcher that accepts standins corresponding to the
     files accepted by rmatcher. Pass the list of files in the matcher
     as the paths specified by the user.'''
     smatcher = getstandinmatcher(repo, rmatcher)
     isstandin = smatcher.matchfn
 
     def composedmatchfn(f):
         return isstandin(f) and rmatcher.matchfn(splitstandin(f))
 
     smatcher.matchfn = composedmatchfn
 
     return smatcher
 
 
 def standin(filename):
     '''Return the repo-relative path to the standin for the specified big
     file.'''
     # Notes:
     # 1) Some callers want an absolute path, but for instance addlargefiles
     #    needs it repo-relative so it can be passed to repo[None].add().  So
     #    leave it up to the caller to use repo.wjoin() to get an absolute path.
     # 2) Join with '/' because that's what dirstate always uses, even on
     #    Windows. Change existing separator to '/' first in case we are
     #    passed filenames from an external source (like the command line).
     return shortnameslash + util.pconvert(filename)
 
 
 def isstandin(filename):
     '''Return true if filename is a big file standin. filename must be
     in Mercurial's internal form (slash-separated).'''
     return filename.startswith(shortnameslash)
 
 
 def splitstandin(filename):
     # Split on / because that's what dirstate always uses, even on Windows.
     # Change local separator to / first just in case we are passed filenames
     # from an external source (like the command line).
     bits = util.pconvert(filename).split(b'/', 1)
     if len(bits) == 2 and bits[0] == shortname:
         return bits[1]
     else:
         return None
 
 
 def updatestandin(repo, lfile, standin):
     """Re-calculate hash value of lfile and write it into standin
 
     This assumes that "lfutil.standin(lfile) == standin", for efficiency.
     """
     file = repo.wjoin(lfile)
     if repo.wvfs.exists(lfile):
         hash = hashfile(file)
         executable = getexecutable(file)
         writestandin(repo, standin, hash, executable)
     else:
         raise error.Abort(_(b'%s: file not found!') % lfile)
 
 
 def readasstandin(fctx):
     '''read hex hash from given filectx of standin file
 
     This encapsulates how "standin" data is stored into storage layer.'''
     return fctx.data().strip()
 
 
 def writestandin(repo, standin, hash, executable):
     '''write hash to <repo.root>/<standin>'''
     repo.wwrite(standin, hash + b'\n', executable and b'x' or b'')
 
 
 def copyandhash(instream, outfile):
     '''Read bytes from instream (iterable) and write them to outfile,
     computing the SHA-1 hash of the data along the way. Return the hash.'''
     hasher = hashutil.sha1(b'')
     for data in instream:
         hasher.update(data)
         outfile.write(data)
     return hex(hasher.digest())
 
 
 def hashfile(file):
     if not os.path.exists(file):
         return b''
     with open(file, b'rb') as fd:
         return hexsha1(fd)
 
 
 def getexecutable(filename):
     mode = os.stat(filename).st_mode
     return (
         (mode & stat.S_IXUSR)
         and (mode & stat.S_IXGRP)
         and (mode & stat.S_IXOTH)
     )
 
 
 def urljoin(first, second, *arg):
     def join(left, right):
         if not left.endswith(b'/'):
             left += b'/'
         if right.startswith(b'/'):
             right = right[1:]
         return left + right
 
     url = join(first, second)
     for a in arg:
         url = join(url, a)
     return url
 
 
 def hexsha1(fileobj):
     """hexsha1 returns the hex-encoded sha1 sum of the data in the file-like
     object data"""
     h = hashutil.sha1()
     for chunk in util.filechunkiter(fileobj):
         h.update(chunk)
     return hex(h.digest())
 
 
 def httpsendfile(ui, filename):
     return httpconnection.httpsendfile(ui, filename, b'rb')
 
 
 def unixpath(path):
     '''Return a version of path normalized for use with the lfdirstate.'''
     return util.pconvert(os.path.normpath(path))
 
 
 def islfilesrepo(repo):
     '''Return true if the repo is a largefile repo.'''
     if b'largefiles' in repo.requirements and any(
         shortnameslash in f[0] for f in repo.store.datafiles()
     ):
         return True
 
     return any(openlfdirstate(repo.ui, repo, False))
 
 
 class storeprotonotcapable(Exception):
     def __init__(self, storetypes):
         self.storetypes = storetypes
 
 
 def getstandinsstate(repo):
     standins = []
     matcher = getstandinmatcher(repo)
     wctx = repo[None]
     for standin in repo.dirstate.walk(
         matcher, subrepos=[], unknown=False, ignored=False
     ):
         lfile = splitstandin(standin)
         try:
             hash = readasstandin(wctx[standin])
         except IOError:
             hash = None
         standins.append((lfile, hash))
     return standins
 
 
 def synclfdirstate(repo, lfdirstate, lfile, normallookup):
     lfstandin = standin(lfile)
     if lfstandin in repo.dirstate:
         stat = repo.dirstate._map[lfstandin]
         state, mtime = stat[0], stat[3]
     else:
         state, mtime = b'?', -1
     if state == b'n':
         if normallookup or mtime < 0 or not repo.wvfs.exists(lfile):
             # state 'n' doesn't ensure 'clean' in this case
             lfdirstate.normallookup(lfile)
         else:
             lfdirstate.normal(lfile)
     elif state == b'm':
         lfdirstate.normallookup(lfile)
     elif state == b'r':
         lfdirstate.remove(lfile)
     elif state == b'a':
         lfdirstate.add(lfile)
     elif state == b'?':
         lfdirstate.drop(lfile)
 
 
 def markcommitted(orig, ctx, node):
     repo = ctx.repo()
 
     orig(node)
 
     # ATTENTION: "ctx.files()" may differ from "repo[node].files()"
     # because files coming from the 2nd parent are omitted in the latter.
     #
     # The former should be used to get targets of "synclfdirstate",
     # because such files:
     # - are marked as "a" by "patch.patch()" (e.g. via transplant), and
     # - have to be marked as "n" after commit, but
     # - aren't listed in "repo[node].files()"
 
     lfdirstate = openlfdirstate(repo.ui, repo)
     for f in ctx.files():
         lfile = splitstandin(f)
         if lfile is not None:
             synclfdirstate(repo, lfdirstate, lfile, False)
     lfdirstate.write()
 
     # As part of committing, copy all of the largefiles into the cache.
     #
     # Using "node" instead of "ctx" implies additional "repo[node]"
     # lookup while copyalltostore(), but can omit redundant check for
     # files comming from the 2nd parent, which should exist in store
     # at merging.
     copyalltostore(repo, node)
 
 
 def getlfilestoupdate(oldstandins, newstandins):
     changedstandins = set(oldstandins).symmetric_difference(set(newstandins))
     filelist = []
     for f in changedstandins:
         if f[0] not in filelist:
             filelist.append(f[0])
     return filelist
 
 
 def getlfilestoupload(repo, missing, addfunc):
     makeprogress = repo.ui.makeprogress
     with makeprogress(
         _(b'finding outgoing largefiles'),
         unit=_(b'revisions'),
         total=len(missing),
     ) as progress:
         for i, n in enumerate(missing):
             progress.update(i)
             parents = [p for p in repo[n].parents() if p != node.nullid]
 
             with lfstatus(repo, value=False):
                 ctx = repo[n]
 
             files = set(ctx.files())
             if len(parents) == 2:
                 mc = ctx.manifest()
                 mp1 = ctx.p1().manifest()
                 mp2 = ctx.p2().manifest()
                 for f in mp1:
                     if f not in mc:
                         files.add(f)
                 for f in mp2:
                     if f not in mc:
                         files.add(f)
                 for f in mc:
                     if mc[f] != mp1.get(f, None) or mc[f] != mp2.get(f, None):
                         files.add(f)
             for fn in files:
                 if isstandin(fn) and fn in ctx:
                     addfunc(fn, readasstandin(ctx[fn]))
 
 
 def updatestandinsbymatch(repo, match):
     '''Update standins in the working directory according to specified match
 
     This returns (possibly modified) ``match`` object to be used for
     subsequent commit process.
     '''
 
     ui = repo.ui
 
     # Case 1: user calls commit with no specific files or
     # include/exclude patterns: refresh and commit all files that
     # are "dirty".
     if match is None or match.always():
         # Spend a bit of time here to get a list of files we know
         # are modified so we can compare only against those.
         # It can cost a lot of time (several seconds)
         # otherwise to update all standins if the largefiles are
         # large.
         lfdirstate = openlfdirstate(ui, repo)
         dirtymatch = matchmod.always()
         unsure, s = lfdirstate.status(
             dirtymatch, subrepos=[], ignored=False, clean=False, unknown=False
         )
         modifiedfiles = unsure + s.modified + s.added + s.removed
         lfiles = listlfiles(repo)
         # this only loops through largefiles that exist (not
         # removed/renamed)
         for lfile in lfiles:
             if lfile in modifiedfiles:
                 fstandin = standin(lfile)
                 if repo.wvfs.exists(fstandin):
                     # this handles the case where a rebase is being
                     # performed and the working copy is not updated
                     # yet.
                     if repo.wvfs.exists(lfile):
                         updatestandin(repo, lfile, fstandin)
 
         return match
 
     lfiles = listlfiles(repo)
     match._files = repo._subdirlfs(match.files(), lfiles)
 
     # Case 2: user calls commit with specified patterns: refresh
     # any matching big files.
     smatcher = composestandinmatcher(repo, match)
     standins = repo.dirstate.walk(
         smatcher, subrepos=[], unknown=False, ignored=False
     )
 
     # No matching big files: get out of the way and pass control to
     # the usual commit() method.
     if not standins:
         return match
 
     # Refresh all matching big files.  It's possible that the
     # commit will end up failing, in which case the big files will
     # stay refreshed.  No harm done: the user modified them and
     # asked to commit them, so sooner or later we're going to
     # refresh the standins.  Might as well leave them refreshed.
     lfdirstate = openlfdirstate(ui, repo)
     for fstandin in standins:
         lfile = splitstandin(fstandin)
         if lfdirstate[lfile] != b'r':
             updatestandin(repo, lfile, fstandin)
 
     # Cook up a new matcher that only matches regular files or
     # standins corresponding to the big files requested by the
     # user.  Have to modify _files to prevent commit() from
     # complaining "not tracked" for big files.
     match = copy.copy(match)
     origmatchfn = match.matchfn
 
     # Check both the list of largefiles and the list of
     # standins because if a largefile was removed, it
     # won't be in the list of largefiles at this point
     match._files += sorted(standins)
 
     actualfiles = []
     for f in match._files:
         fstandin = standin(f)
 
         # For largefiles, only one of the normal and standin should be
         # committed (except if one of them is a remove).  In the case of a
         # standin removal, drop the normal file if it is unknown to dirstate.
         # Thus, skip plain largefile names but keep the standin.
         if f in lfiles or fstandin in standins:
             if repo.dirstate[fstandin] != b'r':
                 if repo.dirstate[f] != b'r':
                     continue
             elif repo.dirstate[f] == b'?':
                 continue
 
         actualfiles.append(f)
     match._files = actualfiles
 
     def matchfn(f):
         if origmatchfn(f):
             return f not in lfiles
         else:
             return f in standins
 
     match.matchfn = matchfn
 
     return match
 
 
 class automatedcommithook(object):
     '''Stateful hook to update standins at the 1st commit of resuming
 
     For efficiency, updating standins in the working directory should
     be avoided while automated committing (like rebase, transplant and
     so on), because they should be updated before committing.
 
     But the 1st commit of resuming automated committing (e.g. ``rebase
     --continue``) should update them, because largefiles may be
     modified manually.
     '''
 
     def __init__(self, resuming):
         self.resuming = resuming
 
     def __call__(self, repo, match):
         if self.resuming:
             self.resuming = False  # avoids updating at subsequent commits
             return updatestandinsbymatch(repo, match)
         else:
             return match
 
 
 def getstatuswriter(ui, repo, forcibly=None):
     '''Return the function to write largefiles specific status out
 
     If ``forcibly`` is ``None``, this returns the last element of
     ``repo._lfstatuswriters`` as "default" writer function.
 
     Otherwise, this returns the function to always write out (or
     ignore if ``not forcibly``) status.
     '''
     if forcibly is None and util.safehasattr(repo, b'_largefilesenabled'):
         return repo._lfstatuswriters[-1]
     else:
         if forcibly:
             return ui.status  # forcibly WRITE OUT
         else:
             return lambda *msg, **opts: None  # forcibly IGNORE

tests/test-lfs-bundle.t

@@ -1,97 +1,126 b''
 In this test, we want to test LFS bundle application on both LFS and non-LFS
 repos.
 
 To make it more interesting, the file revisions will contain hg filelog
 metadata ('\1\n'). The bundle will have 1 file revision overlapping with the
 destination repo.
 
 #  rev      1          2         3
 #  repo:    yes        yes       no
 #  bundle:  no (base)  yes       yes (deltabase: 2 if possible)
 
 It is interesting because rev 2 could have been stored as LFS in the repo, and
 non-LFS in the bundle; or vice-versa.
 
 Init
 
   $ cat >> $HGRCPATH << EOF
   > [extensions]
   > lfs=
   > drawdag=$TESTDIR/drawdag.py
   > [lfs]
   > url=file:$TESTTMP/lfs-remote
   > EOF
 
 Helper functions
 
   $ commitxy() {
   > hg debugdrawdag "$@" <<'EOS'
   >  Y  # Y/X=\1\nAAAA\nE\nF
   >  |  # Y/Y=\1\nAAAA\nG\nH
   >  X  # X/X=\1\nAAAA\nC\n
   >     # X/Y=\1\nAAAA\nD\n
   > EOS
   > }
 
   $ commitz() {
   > hg debugdrawdag "$@" <<'EOS'
   >  Z  # Z/X=\1\nAAAA\nI\n
   >  |  # Z/Y=\1\nAAAA\nJ\n
   >  |  # Z/Z=\1\nZ
   >  Y
   > EOS
   > }
 
   $ enablelfs() {
   >   cat >> .hg/hgrc <<EOF
   > [lfs]
   > track=all()
   > EOF
   > }
 
 Generate bundles
 
   $ for i in normal lfs; do
   >   NAME=src-$i
   >   hg init $TESTTMP/$NAME
   >   cd $TESTTMP/$NAME
   >   [ $i = lfs ] && enablelfs
   >   commitxy
   >   commitz
   >   hg bundle -q --base X -r Y+Z $TESTTMP/$NAME.bundle
   >   SRCNAMES="$SRCNAMES $NAME"
   > done
 
 Prepare destination repos
 
   $ for i in normal lfs; do
   >   NAME=dst-$i
   >   hg init $TESTTMP/$NAME
   >   cd $TESTTMP/$NAME
   >   [ $i = lfs ] && enablelfs
   >   commitxy
   >   DSTNAMES="$DSTNAMES $NAME"
   > done
 
 Apply bundles
 
   $ for i in $SRCNAMES; do
   >   for j in $DSTNAMES; do
   >     echo ---- Applying $i.bundle to $j ----
   >     cp -R $TESTTMP/$j $TESTTMP/tmp-$i-$j
   >     cd $TESTTMP/tmp-$i-$j
   >     if hg unbundle $TESTTMP/$i.bundle -q 2>/dev/null; then
   >       hg verify -q && echo OK
   >     else
   >       echo CRASHED
   >     fi
   >   done
   > done
   ---- Applying src-normal.bundle to dst-normal ----
   OK
   ---- Applying src-normal.bundle to dst-lfs ----
   OK
   ---- Applying src-lfs.bundle to dst-normal ----
   OK
   ---- Applying src-lfs.bundle to dst-lfs ----
   OK
+
+Hint if the cache location cannot be inferred from the environment
+
+#if windows
+  $ unset LOCALAPPDATA
+  $ unset APPDATA
+  $ HGRCPATH= hg config lfs --debug
+  abort: unknown lfs usercache location
+  (define LOCALAPPDATA or APPDATA in the environment, or set lfs.usercache)
+  [255]
+#endif
+
+#if osx
+  $ unset HOME
+  $ HGRCPATH= hg config lfs --debug
+  abort: unknown lfs usercache location
+  (define HOME in the environment, or set lfs.usercache)
+  [255]
+#endif
+
+#if no-windows no-osx
+  $ unset XDG_CACHE_HOME
+  $ unset HOME
+  $ HGRCPATH= hg config lfs --debug
+  abort: unknown lfs usercache location
+  (define XDG_CACHE_HOME or HOME in the environment, or set lfs.usercache)
+  [255]
+#endif
+