[BUG][MERGE] 'bzr upgrade' broken by lazy imports

[Aaron Bentley]

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John Arbash Meinel wrote:
> I fixed this specific dependency with the attached patch. I'd like to
> get it merged quickly. Also, we need to decide if it is worth releasing
> an 0.12.1. It is a regression, though the simple workaround is to just
> install bzrtools (which imports bzrlib.workingtree as part of it's startup).

Hmm.  The code in question doesn't seem to be under test.  At least,
when I remove bzrtools and run 'bzr selftest upgrade', no errors are
produced.

> I chose to fix this by doing 'from bzrlib.workingtree import Foo' rather
> than changing the global imports, because that is how all the other
> local functions work. And probably that is because of an import
> dependency issue. One nice thing about lazy imports is that they solve
> some import order issues, since you won't import something until it is used.

I agree being minimalist makes sense for this kind of bugfix.

> My initial feeling is to just change most code paths that use
> 'bzrilb.foo' to being 'from bzrlib import foo' at the beginning, and use
> 'foo.bar' later on.

That seems okay.

> === modified file bzrlib/bzrdir.py
> --- bzrlib/bzrdir.py
> +++ bzrlib/bzrdir.py
> @@ -1870,11 +1870,12 @@
>                  if name in bzrcontents:
>                      self.bzrdir.transport.delete(name)
>          else:
> +            from bzrlib.workingtree import WorkingTreeFormat3
>              self.step('Upgrading working tree')
>              self.bzrdir.transport.mkdir('checkout', mode=self.dir_mode)
>              self.make_lock('checkout')
>              self.put_format(
> -                'checkout', bzrlib.workingtree.WorkingTreeFormat3())
> +                'checkout', WorkingTreeFormat3())
>              self.bzrdir.transport.delete_multi(
>                  self.garbage_inventories, self.pb)
>              for entry in checkout_files:

This looks okay, but is there any way we can test it?

Aaron
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