Case-only renames on Windows (issue #3702)

Hi,

I'm looking at issue #3702 ("svn ren TODO todo" not work on windows).
Although this is marked as "1.7-consider", I'd really like this to be
fixed before release, since this is pretty important for me and my
user base. So I'd like to take a stab, but being relatively
inexperienced, I'd like some help ... OTOH, if someone more
experienced can fix this easily, that would be fine too :-).

As explained by Bert in

    http://subversion.tigris.org/issues/show_bug.cgi?id=3702#desc6

the remaining issue here is that the command line client normalizes
all paths to their on-disk casing, before passing the paths to the
client layer. Or, following the code:

svn/move_cmd.c#svn_cl__move:
    -> svn/util.c#svn_cl__args_to_target_array_print_reserved
        -> libsvn_client/cmdline.c#svn_client_args_to_target_array
            -> libsvn_subr/opt.c#svn_opt__arg_canonicalize_path
                -> apr_filepath_merge(... APR_FILEPATH_TRUENAME ...)
                   ^^^ normalizes case, as indicated by flag ^^^
    ...
    -> pick dst_path of the list of targets
    ...
    -> call libsvn_client/copy.c#svn_client_move6

So: all the target paths of the command are normalized first, and only
after that the dst_path is taken as the last target. By then it's
already transformed to on-disk-casing. I don't really know how to go
about this.

Some thoughts:

- There is only a problem if the dst_path gets case-normalized to one
of the source paths. Otherwise, the case-normalization really does
need to happen.

- Maybe: let it be case-normalized like it is now, together with
everything else, but check afterwards if it's now identical to one of
the source paths. If so, transform back to the original case? Or throw
it again through a canonicalization routine, but without changing
case?

- Since svn_cl__args_to_target_array_print_reserved and lower are
blissfully unaware about what the targets are for (source or dest),
the only place to start the "alternative path" for handling dst_path
would be move_cmd.c#svn_cl__move itself.

- Other useful things happen inside svn_client_args_to_target_array
and svn_opt__arg_canonicalize_path (and in apr_filepath_merge modulo
the APR_FILEPATH_TRUENAME flag), besides the case-normalization. Those
other things probably also need to be done to dst_path, even if it's
not case-normalized. Is there already some code for that?

Any input is appreciated.

How do other svn clients handle this (or will handle this)?

Cheers,

-- 
Johan