[PATCH RFC] dirstate: ignore symlinks when fs cannot handle them (issue1888)

[Martin Geisler]

# HG changeset patch
# User Martin Geisler <mg at aragost.com>
# Date 1279635966 -7200
# Node ID b58176972fb53e02a396f0f5be82a765723ce98b
# Parent  fda0e478fb7945b15110738885b8f54bcf2ff576
dirstate: ignore symlinks when fs cannot handle them (issue1888)

When the filesystem cannot handle the executable bit, we currently
ignore it completely when looking for modified files. Similarly, it is
impossible to set or clear the bit when the fs ignores it.

This patch makes Mercurial treat symbolic links the same way.

Symlinks are a little different since they manifest themselves as
small files containing a filename (the symlink target). On Windows,
these files show up as regular files, and on Linux and Mac they show
up as real symlinks.

Issue1888 presents a case where the symlink files are better ignored
from the Windows side. A Linux client creates symlinks in a working
copy which is shared over a network between Linux and Windows clients.

The Samba server is helpful and defererences the symlink when the
Windows client looks at it. This means that Mercurial on the Windows
side sees file content instead of a file name in the symlink, and
hence flags the link as modified. Ignoring the change would be much
more helpful, similarly to how Mercurial does not report any changes
when executable bits are ignored in a checkout on Windows.

An initial checkout of a symbolic link on a file system that cannot
handle symbolic links will still result in a regular file containing
the target file name as its content. Sharing such a checkout with a
Linux client will not turn the file into a symlink automatically, but
'hg revert' can fix that. After the revert, the Windows client will
see the correct file content (provided by the Samba server when it
follows the link on the Linux side) and otherwise ignore the change.

diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -625,6 +625,9 @@
         dadd = deleted.append
         cadd = clean.append
 
+        lnkkind = stat.S_IFLNK
+        ignorelinks = not self._checklink
+
         for fn, st in self.walk(match, subrepos, listunknown,
                                 listignored).iteritems():
             if fn not in dmap:
@@ -640,6 +643,8 @@
             if not st and state in "nma":
                 dadd(fn)
             elif state == 'n':
+                if ignorelinks and mode & lnkkind:
+                    continue
                 if (size >= 0 and
                     (size != st.st_size
                      or ((mode ^ st.st_mode) & 0100 and self._checkexec))

-- 
Martin Geisler

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