Patchwork [bugfix] Skip repositories not readable with current privileges; skip empty “.hg” directories, e.g. unmounted mountpoints

diff --git a/contrib/bash_completion b/contrib/bash_completion
--- a/contrib/bash_completion
+++ b/contrib/bash_completion
@@ -75,8 +75,10 @@  shopt -s extglob
 _hg_repos()
 {
     local i
-    for i in $(compgen -d -- "$cur"); do
-	test ! -d "$i"/.hg || COMPREPLY=(${COMPREPLY[@]:-} "$i")
+    for i in $( compgen -d -- "$cur" ) ;  do
+	[[ -r "$i/.hg/requires" \
+	    || -r "$i/.hg/00changelog.i" ]] \
+            && COMPREPLY+=( "$i" )
     done
 }
 
diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -9,6 +9,7 @@  from node import hex, nullid, nullrev, s
 from i18n import _
 import os, sys, errno, re, tempfile
 import util, scmutil, templater, patch, error, templatekw, revlog, copies
+from readable_repository import readable_repository
 import match as matchmod
 import subrepo, context, repair, graphmod, revset, phases, obsolete
 import changelog
@@ -72,7 +73,7 @@  def findcmd(cmd, table, strict=True):
     raise error.UnknownCommand(cmd)
 
 def findrepo(p):
-    while not os.path.isdir(os.path.join(p, ".hg")):
+    while not readable_repository(p):
         oldp, p = p, os.path.dirname(p)
         if p == oldp:
             return None
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -10,6 +10,7 @@  import peer, changegroup, subrepo, disco
 import changelog, dirstate, filelog, manifest, context, bookmarks, phases
 import lock, transaction, store, encoding
 import scmutil, util, extensions, hook, error, revset
+from readable_repository import readable_repository
 import match as matchmod
 import merge as mergemod
 import tags as tagsmod
@@ -191,7 +192,7 @@  class localrepository(object):
         else:
             self.supported = self._basesupported
 
-        if not self.vfs.isdir():
+        if not readable_repository(self.root):
             if create:
                 if not self.wvfs.exists():
                     self.wvfs.makedirs()
diff --git a/mercurial/readable_repository.py b/mercurial/readable_repository.py
new file mode 100644
--- /dev/null
+++ b/mercurial/readable_repository.py
@@ -0,0 +1,23 @@ 
+# readable_repository.py
+#       check if there is a readable, valid mercurial repository in the
+#       given "reporoot" directory
+#
+# Copyright 2013 Matt Mackall <mpm@selenic.com>, Roland Eggner <edv@systemanalysen.net>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+import os
+
+def readable_repository(reporoot):
+    # Assumptions:
+    # In valid revlogv1 and later repositories there is always a readable file '.hg/requires'.
+    # In valid revlogv0 repositories there is always a readable file '.hg/00changelog.i'.
+    # Targets:
+    # Skip empty '.hg' directories, e.g. currently not mounted mount points.
+    # Skip repositories unreadable with current privileges.
+    reporoot_hg = os.path.join(reporoot, '.hg')
+    return (os.path.isdir(reporoot_hg)
+        and ((os.path.isfile(os.path.join(reporoot_hg, 'requires'     )) and os.access(os.path.join(reporoot_hg, 'requires'     ), os.R_OK))
+        or   (os.path.isfile(os.path.join(reporoot_hg, '00changelog.i')) and os.access(os.path.join(reporoot_hg, '00changelog.i'), os.R_OK))))
+
diff --git a/mercurial/scmutil.py b/mercurial/scmutil.py
--- a/mercurial/scmutil.py
+++ b/mercurial/scmutil.py
@@ -8,6 +8,7 @@ 
 from i18n import _
 from mercurial.node import nullrev
 import util, error, osutil, revset, similar, encoding, phases, parsers
+from readable_repository import readable_repository
 import match as matchmod
 import os, errno, re, stat, glob
 
@@ -516,7 +517,7 @@  def walkrepos(path, followsym=False, see
         adddir(seen_dirs, path)
     for root, dirs, files in os.walk(path, topdown=True, onerror=errhandler):
         dirs.sort()
-        if '.hg' in dirs:
+        if readable_repository(root):
             yield root # found a repository
             qroot = os.path.join(root, '.hg', 'patches')
             if os.path.isdir(os.path.join(qroot, '.hg')):