Revision properties
===================

.. contents:: :local:


Motivation
----------
At the moment, Bazaar revision properties and metadata are stored in file 
properties on the branch root. Getting the revision properties for a series of
revisions currently requires iterating over all of these revisions and calling 
svn_ls() on the branch root of the revision itself and the revision before 
that to obtain the properties set. 

This has several disadvantages:

 - svn_ls() is quite expensive and slow
 - file property changes are picked up by "svn diff" and commit notification 
   mailers. They should rather be ignored.
 - they require you to know the branch root before being able to do anything

Subversion custom revision property support
-------------------------------------------
Subversion supports storing custom revision properties. In older versions (pre 
1.5), setting these revision properties is only possible after committing. This 
also requires the change of the revision property to be accepted by the 
pre-change-revprop hook, which is disabled by default.

Subversion 1.5 allows setting custom revision properties as part of commit, 
without the need to change any hooks on the server side. It also supports 
iterating over custom revision properties using svn_ra_log().

This should allow for a massive performance improvement and user experience. 
However, the problem is that this will not work with a lot of older Subversion 
repositories.

Legacy repositories
~~~~~~~~~~~~~~~~~~~
There are already repositories out there that have the old file properties 
set (version 3 and lower of the bzr<->svn mappings). In order to interoperate 
with existing versions of bzr-svn that support file properties only, 
file properties should always be set together with revision properties.

In order to make sure that it is possible to rely on revision properties 
as much as possible, the following policy will be followed where it concerns 
pushing new revisions:

- Set both file properties and revision properties unless support_legacy is 
  set to False or the previous revision with revprops set didn't have file 
  props set
- Refuse to set revision properties unless all revisions since the last 
  revision with bzr revision properties contain no bzr file props or contain 
  both bzr file props and bzr revprops. When revprops are seen, scan only for 
  file properties since that point 

Upgrade command
~~~~~~~~~~~~~~~
`bzr svn-upgrade` needs to support being run on a Subversion repository or a 
new command should be added to allow setting matching revision properties for 
the existing file properties. This will iterate over the repository since the 
last revision with revprops set and set matching revision properties for each 
revision with file props.

New settings
~~~~~~~~~~~~
A new per-Subversion-repository setting `support_legacy` will be added. This 
setting controls whether file properties should be set when pushing to the 
specified repository. It defaults to True.

..  vim: ft=rest