Split and join files
====================

Version control systems tend to have trouble when files are split or
joined.  Here is one possibility for handling that.


Splitting files
---------------

This can work like 'svn cp': copy with history::

  % bzr cp a b

This creates a new file b, whose file-history is the same as a, but
with a different file-id, and present at a different name.

This creates the slightly strange situation that b claims to have text
versions for revisions where b was not actually present.


Joining files
-------------

We might want to also join files in various cases:

 * Multiple imports of the same file

 * Two source files are being refactored into a single one

 * Two people apply an external patch that creates the same file

I'm not aware of any other system that handles this.

  % bzr join a b

a and b must be versioned files.  b is removed from the working tree
and inventory.  b's file id is added as a secondary id as a, so that
later merges between them will detect them as being the same.  

b's weave is (???) incorporated into a.  

This means that we have a file which has multiple history paths.  For
example, asking to compare that file to its state in a previous
version has to arbitrarily pick one to use.  That's not necessarily
fatal if we assign one as primary, but it might be a bit confusing.
Trying to merge from another tree might can't really choose a good
basis.



File aliases
------------

Rather than trying to join files we might just add notes that files
are also known by a different file-id in other trees.