drush support for rsync version lower than 2.6.9

Shouldn't have assigned this to myself; someone else should review.

This can also affect pm-download; see #961134: When i download code via drush i get rsync error.

Hm, thought that the rsync on my server that's using protocol version 29 was 2.6.8, but no matter; seems we don't need to support protocol version 28 or earlier, since rsyncs that old do not support a key feature needed by sql-sync and pm-download. Thanks.

The option --remove-source-files in protocol 30 is called --remove-sent-files in protocol 29. With this patch, if you set --protocol=29, then it causes drush to automatically rename the protocol-30 option to its protocol-29 name, so that your code can invariantly use --remove-source-files (as sql-sync and pm-download do).

This is what man rsync says in 2.6.8:

       --remove-sent-files
              This  tells  rsync  to  remove  from  the sending side the files
              and/or symlinks that are  newly  created  or  whose  content  is
              updated  on the receiving side.  Directories and devices are not
              removed, nor are  files/symlinks  whose  attributes  are  merely
              changed.

This is what man rsync says in 3.0.6:

       --remove-source-files
              This tells rsync to remove  from  the  sending  side  the  files
              (meaning  non-directories)  that  are a part of the transfer and
              have been successfully duplicated on the receiving side.

You are correct that remove sent files will occasionally leave something behind, but only if it exists and has the same content as the source file. This should never be the case for pm-download, which now deletes the target first. For sql-sync, you could leave a temporary dump file behind if there were absolutely no changes to the database, and you are using postgres. Under mysql, timestamps are included in the dump, so they are always different every time, even if the db has not changed.

Since the behavior is close, and there is no available alternative, I think that reverting to --remove-sent-files is reasonable.

Regarding --protocol=29, I choose that because that option is passed on to rsync; however, this reasoning is spurious, as this option only affects batch mode. Direct transfers will automatically adjust the protocol versions to match. I still prefer --protocol=29 to something vague like "old" version or something long like lower-than-2.6.9.

I see your point, though; I misread what you said in #3 the first time, that --protocol=29 is not accurate. Perhaps "old" is better? Opinions?

I guess the thing is (for me) that regardless of length, 2.6.9 is a bit of a mouthful. How about --use-legacy-rsync, or just --legacy-rsync?

$options['rsync-version'] = 2.6.8; would require more code, though, as you would need to make sure that 2.12.8 is considered to be a later version than 2.2.8. Maybe convert them into 21208 and 20208 before comparison?

Here is an updated patch per #14 with docs in example.drushrc.php.

Good point. Here is an improved patch that gracefully degrades for rsync versions earlier than 2.6.3, and improves the explanatory text in examples.drush.rc to match.

Any objections to committing this?

Yes, that was my plan, but I wanted to commit this first rather than tangle the two. But I'll tangle here if that's preferable, esp. since drush_move_dir has been committed.

Committed, but forgot to set status.

http://drupal.org/cvs?commit=453986