[MERGE] Improve warning to 'bzr upgrade' to specify --rich-root or --subtree if needed.

[John Arbash Meinel]

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Andrew Bennetts wrote:
| This patch improves the warning you see when you use an old repository to
| suggest “bzr upgrade --rich-root” or “bzr upgrade --subtree” if
necessary.  This
| would have helped Russel Winder, who got bitten by doing what the
warning said
| only to find that “bzr upgrade” failed.
|
| To support this, I added a “supports_tree_reference” method to
Repository (with
| trivial per-implementation test), to match the supports_rich_root
method it
| already has.  This wasn't strictly necessary, but I expect it will be
useful for
| RemoteRepository sooner or later (for RemoteRepository it's much easier if
| format features are checked via the repository instance than via a
format).
|
| I also added a hidden format called “subtree”, so that bzr upgrade
- --subtree
| would work.  It's an alias for pack-0.92-subtree at the moment.  I
think this is
| a reasonable alias to have, after all we already have --rich-root.
|
| This is related to <https://bugs.launchpad.net/bzr/+bug/252908>.  It
doesn't fix
| that bug, but it does make it less urgent.
|
| One nice thing about extending the warning message this way is that it
is a
| reminder to the user that their repository is not in a default format.
  So I
| think this is a good improvement to have, even if we do fix 252908
soon as well.
|
| -Andrew.
|
|

Well --rich-root is actually Knit format + rich roots. So it isn't
really the same thing as what you are proposing for --subtree.

Since we don't actually have another alias, I would rather not recommend
- --subtree.

Because they actually have to do:

bzr upgrade --rich-root-pack

though with 1.6 now, we would have them do:

bzr upgrade --1.6-rich-root

Also, we are trying to get people away from the -subtree format as it is
more experimental than the rest. There is a "happy" side-effect that you
can do "bzr init --rich-root-pack ; bzr pull ../my-subtree-repo" as long
as you don't actually use subtrees.

(It is technically a bug that pull lets you do this, though you *could*
argue that upgrade should work under the same conditions.)

BB:resubmit

So I think your recommendations are actually wrong, but otherwise I like
the idea to have people use upgrade that will actually, you know, *work*. :)

John
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