[RFC] weave refactoring

[Martin Pool]

On 11 Dec 2005, Johan Rydberg <jrydberg at gnu.org> wrote:
> Hi,
> 
> In my efforts to implement the knit history format I've begun a
> refactoring work of things in bzrlib that operates on versioned files;
> i.e., weaves.  I've created an abstract class called VersionedFile,
> and a store type to come with it; VersionedFileStore.
> 
> I renamed control_weaves to control_store, and weave_store to
> file_store. revision_store is left untouched at this moment.
> 
> To test the concept I implemented WeaveVersionedFile, and changed
> WeaveStore to implement the VersionedFileStore API.  It took some
> effort, but _almost_* all tests pass.  There is also some code that is
> hard to adopt to the new API; the weave merge being one.  Right now it
> knows about the internals of WeaveVersionedFile.
> 
> The code can be found at:
> 
>   http://repo.panadafs.org/bzr/bzr.jrydberg.versionedfile/

This looks like a very good direction to me.

Weave could almost implement VersionedFile directly, but perhaps it's
better to keep just the datastructure in Weave and coordinate with the
store in WeaveVersionedFile.

I think I'd handle weave merge like this: ask the VersionedFile for its
representation as a Weave.  (Like asking it for that interface).  Allow
this to raise an exception if the file is stored in a way that's not
either a weave or convertible to a weave; this should terminate the
merge.

For upgrades: the code that's currently in upgrade is really for a
specific type of upgrade to a particular version.  There should be tests
that it still works so that we can write out previous formats but you
can use different upgrade code to go to a new format.

-- 
Martin
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