[RFC][MERGE] case sensitivity on Windows

[John Arbash Meinel]

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Mark Hammond wrote:
> [Resending as bundle-buggy missed it before...]

You have to start with [MERGE][RFC] or [MERGE/RFC], starting with [RFC]
prevents bundle buggy from finding it.

> 
> -------- Original Message --------
> Subject: RE: [RFC/MERGE] case sensitivity on Windows
> Date: Tue, 18 Nov 2008 10:49:19 +1100
> From: Mark Hammond <mhammond at skippinet.com.au>
> To: 'Martin Pool' <mbp at canonical.com>
> CC: 'Bazaar' <bazaar at lists.canonical.com>
> 
> [Martin writes]
> 
>> I don't think you should write against the internals of the dirstate.
>>  Instead, walk down through the inventory, just like you do in the
>> filesystem.  For each directory, look through its .children list
>> case-insensitively, to find the actual name of the next component of
>>  the path.
> 
> Doh!  Yeah - that is a lot easier :)
> 
> I've attached a new patch which implements this and addresses your other
> comments from the earlier review.  Although this doesn't complete the
> support for case-insensitive file-systems, it is a good step towards
> that and should cause no regressions.  However, I expect there to be a
> few main areas of concern:
> 
> * The names of the functions:
> 
> - osutils.canonical_relpath() - like osutils.relpath(), and named "in
>   its spirit"
> - WorkingTree.canonical_relpath() - like WorkingTree.relpath(), also
>   named in its spirit
> - Tree.get_canonical_path() to perform the case-insensitive search of
>   the inventory.  Named 'in the spirit' of existing methods
>   Tree.get_symlink_target(), Tree.get_file_by_path(), Tree.get_file(), etc
> 
> The end result is 2 sets of functions that perform similar functions,
> but in different ways - but that problem seems to already exist -
> Tree.get_file(), Tree.get_symlink_target() all work on the inventory,
> but their name gives no indication it isn't actually looking at a
> WorkingTree on disk.  I welcome better names.
> 
> * The performance of Tree.get_canonical_path() when an 'invalid' name is
> specified.  If the input arg is the name of an existing item, I expect
> the performance will be OK as the name is looked up as specified.
> However, if the name specifies an inventory item that does *not* exist,
> we will walk the inventory as deeply as we can find matches.  OTOH, it
> would seem rare that non-existing items are passed on the cmdline.  We
> may want to restrict use of this function to Windows, but as noted in
> previous comments, this functionality isn't actually restricted to
> Windows (think FAT32 devices on Linux), so advice on how to best
> approach this is needed.  My testing on Linux shows no regressions
> caused by this patch as it stands.

We already detect whether the filesystem that the WT is on is
case-insensitive. As part of WT.__init__ we call:

def _detect_case_handling(self):
    wt_trans = self.bzrdir.get_workingtree_transport(None)
    try:
        wt_trans.stat("FoRMaT")
    except errors.NoSuchFile:
        self.case_sensitive = True
    else:
        self.case_sensitive = False

    self._setup_directory_is_tree_reference()

So you can just check:

if self.case_sensitive:
  ...
else:
  ... #use canonical_path()


John
=:->

> 
> * There is a new "expected failure" relating to a remaining limitation
> in 'bzr add'; as noted in the exception message, I believe that to
> resolve this it might be necessary to move the case_sensitive attribute
> up the chain from WorkingTree into MutableTree, or otherwise push the
> required functionality down into WorkingTree.
> 
> 
> Thanks,
> 
> Mark
> 
> 

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