[RFC] CURRENT_TREE_REVISION ?

[Aaron Bentley]

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Robert Collins wrote:
> I'm thinking of adding a new special revision marker, like null: is
> today, which will be current:.
> 
> add_revision and get_revision will guard against this being
> stored/retrieved.
> 
> It will be the revision id for the working tree.

I've thought about doing the same thing for quite a while.  It feels
somewhat icky to have a revision-id for something that's not a revision
(yet), but it solves a bunch of problems, so I'm +1 overall.

I'm not sure current: is the clearest thing-- I immediately thought it
meant WorkingTree.last_revision().  Maybe 'directory:'?

> This allows the following things without [much?|any?] special casing:
> 
> * bzr log can show the pending merges as being merged into the current
> tree.

(some formatting issues, though.  Log output is designed so the merging
revision comes first.)

> Possibly there are other applications for it.

Bzr revert and shelve can use it to create bundles for the working tree
instead of backup files or patches.

"bzr merge -r -1..revid:current: foo" can be used can be used to copy
uncommitted changes from foo.  (See also bzrtools shove, though.)

> I'm thinking of an api like 'tree.get_revision()' to get the revision
> object that owns a tree. For EmptyTree this is a Revision object
> representing 'null:', for WorkingTree this is a Revision object
> representing 'current:' with parents matching the parents list of the
> tree - i.e. null: for a newly inited tree.

RevisionTrees already have a revision_id member, so we chould just
provide that to the others.

One downside to this idea is that the 'current:' revision id doesn't
have a fixed meaning, and two trees with that revision id may not refer
to the same thing.

Aaron
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