** Proposed new commit system **


Purpose:  

  1.  [speed] Detect conflicts early: without ever seeing a bit of
      svndiff data

  2.  [speed] Less merging:  always merging against head.

  3.  [speed] Zero undeltification: detect conflicts without having
      to undeltify directories.

  4.  [theory] Unified commit-system across RA implementations;
      guarantees that "Hudson" scenarios will consistently work.


Status Quo:

  The first two advantages listed above are already being achieved by
  ra_dav in its own way, so for a long time the 3rd point was our
  motivating force.  However, because undeltification isn't so
  horrible anymore, we've prioritized this task as Beta.

  But now point #4 has come into play;  as long as we put off this
  task, ra_dav will have two theoretical deficiencies:

      * to replace a file, the user must {delete, add, commit}.  If
        the user attempts to {delete, commit, add, commit}, the second
        commit will fail.

      * unable to prevent users from committing propchanges on
        out-of-date dirs.  Thus users could end up with working copies
        containing dirs whose revision numbers are incorrect.


Another TODO:      

  We would like to get rid of the ghudson-scenario 'deleted' existence
  flag in the working copy.  It makes the commit-crawler insanely
  complex.  

   Here's how:

      - 'deleted' flag is only needed in the commit case, because the
        crawler is assuming that it's building a perfect mirror of the
        working copy on the server (which is true with ra_local).
        After our commit process is always merging against HEAD
        on-the-fly, we no longer need to send extra delete commands.

      - 'deleted' flag is used during updates, where we really *are*
        always building a perfect mirror of the working copy on the
        server.  But we don't *have* to build a perfect mirror;  if we
        left out the extra deletes, then dir_deltas will send us back
        an extra delete.  This isn't a problem if we make the update
        editor treat an 'extra' delete as a no-op!


-----------------------------------------------------------------------

Key:  HEAD  := the latest revision number in the repository
      NRID  := Node-Rev-ID of some object in HEAD revision
      CR    := Created Revision;  the revision in which NRID was created



--

Editor:     RA->get_commit_editor()

ra_local:   Fetches editor from libsvn_repos, composes with tracking editor.

ra_dav:     Has own editor, composes with tracking editor.
            Creates a transaction (MKACTIVITY) based on HEAD. (### too early!)
            Sets the log message on the transaction:
                (CHECKOUT baseline;  PROPPATCH baseline)

new system: ?

--

Editor:     set_target_revision (rev)

comment:    [Not used by the commit driver.  This is for updates.]

---

Editor:     replace_root (rev)

ra_local:   Creates a transaction based on REV.

ra_dav:     Ignores REV;  gets versioned-resource-url from working copy.

new system: Creates a transaction based on HEAD.

--

Editor:     add_directory/file (name, copyfrom_path, copyfrom_rev)

ra_local:   Normally calls fs_make_dir() or fs_make_file().
            If copyfrom args, then fs_copy() instead.

ra_dav:     CHECKOUT parent into activity.
            if dir, MKCOL. (could return out-of-date error?).
            if file, do nothing.
                   (--> currently ignores copyfrom) (### bad)

new system: look up path in transaction (HEAD)
            if path exists already, return out-of-date error.
            else:
               do what ra_local does.

--

Editor:     replace_file/dir (name, rev)

ra_local:   If REV != parent's rev, fs_link() the different file into
            the transaction.

ra_dav:     Ignores REV.
            If dir, just telescope the baton's path.
            If file, CHECKOUT the file/dir into the activity.
                    (could return out-of-date error?)

new system: look up the path in the transaction (HEAD).
            if path non-existent, return out-of-date error.
            else:  (### ?file only?)
              get CR of path, by examining path's NRID.
              if (REV < CR), return out-of-date error.
              if (CR <= REV <= HEAD), do nothing, all is good.

--

Editor:     delete_entry (name)

ra_local:   Calls fs_delete_tree().

ra_dav:     CHECKOUT parent into activity.
            DELETE object.  (### this should not return an out-of-date error)

new system: look up the path in the transaction (HEAD).
            if path non-existent, go home.  (merge allows this)
            else:
              get CR of path, by examining path's NRID.
              if (REV < CR), return out-of-date error.
              if (CR <= REV <= HEAD), remove the object from the transaction.
             
--

Editor:     apply_textdelta ()

ra_local:   returns window handler from fs_apply_textdelta().

ra_dav:     returns window handler that writes to tmp file.
            when stream is closed, do a PUT of the file
                                   (could return out-of-date error?)

new system: ?

--

Editor:     change_file/dir_prop (name, val)

ra_local:   Calls fs_change_node_prop()

ra_dav:     CHECKOUT the object.
            Cache the propchange.

new system: ?

--

Editor:     close_file/dir ()

ra_local:   frees batons.

ra_dav:     Send cached propchanges via PROPPATCH.

new system: ?


--

Editor:     abort_edit ()

ra_local:   Calls fs_abort_txn()

ra_dav:     Non-existent!!! (### bad)

new system: ?


--

Editor:     close_edit ()

ra_local:   Calls fs_commit_txn().  All conflicts are found at this time.
            If merge works, then (selectively) bumps revisions.

ra_dav:     Sends MERGE request:  "please merge this activity"
            mod_dav_svn calls fs_commit_txn().
            mod_dav_svn runs dir_delta() on new revision to generate response.
            ra_dav parses response and (selectively) bumps revisions/wcprops.

new system: ?