[#93583] tagging in empty repository

[Martin Pool]

https://bugs.launchpad.net/bzr/+bug/93853

I was just looking at some leftover code in my tags branch and came
upon this bug.  The original problem report was that running 'bzr tag'
in a branch with no revisions gave a traceback.  That's now fixed;
doing this creates a tag pointing to 'null:', which I guess is
reasonable.  However it looks like we'd also reviewed a patch from Tim
Hatch that gives an error if you try to tag the null revision:

+
+
+    def test_tag_null_revision(self):
+        # see bug 93853 - up to 0.18, tag in an empty branch failed
+        tree = self.make_branch_and_tree('.')
+        self.run_bzr_error(['This branch has no revisions to tag.'],
+                           'tag mytagname')
+        self.run_bzr_error(['The null revision may not be tagged.'],
+                           'tag -r0 mytagname')

So it's basically just a 'protect users from themselves' vs 'do what i
say' tradeoff.

As the bug is already closed I propose to just leave thing as they
stand, unless anyone really wants to put in this behavior.

-- 
Martin