tree conflicts and obstructions

Hello Steve, Julian, Nico, and others interested,

One of the failing tests on the tree-conflicts branch shows that
we have a gap in the design.

Namely, we have not yet defined how svn should behave if a file
is obstructed by an unversioned item of the same name during
update/switch and merge.

See http://subversion.tigris.org/issues/show_bug.cgi?id=3139

Currently, during update and switch obstructions cause the operation
to fail:
svn: Failed to add file 'b': object of the same name already exists

I think this behaviour suits us fairly well already.

But obstructed files are currently silently skipped during merge!

I suppose we should flag obstructed files as tree conflict
victims during merge, except when their name appears in the
svn:ignore property on the containing directory.

Opinions?

Julian has already expressed implicit consent in
http://subversion.tigris.org/servlets/ReadMsg?list=dev&&msgNo=136402 ,
but I want to make sure everyone agrees with us here.

We should update detection.txt accordingly, and possibly also
use-cases.txt.

-- 
Stefan Sperling <stsp_at_elego.de>                 Software Developer
elego Software Solutions GmbH                            HRB 77719
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http://www.elego.de                 Geschaeftsfuehrer: Olaf Wagner