decoratedresultset does not support prejoins

If you see
"File "lib/lp/bugs/browser/tests/bug-views.txt", line 961, in bug-views.txt
Failed example:
    for bug in view.similar_bugs:
        print "Bug %s: %s" % (bug.id, bug.title)
Exception raised:
    Traceback (most recent call last):
      File "/usr/lib/python2.6/doctest.py", line 1248, in __run
        compileflags, 1) in test.globs
      File "<doctest bug-views.txt[274]>", line 1, in <module>
      File "/home/robertc/launchpad/lp-branches/working/lib/canonical/cachedproperty.py", line 220, in __get__
        result = self.fn(inst)
      File "/home/robertc/launchpad/lp-branches/working/lib/lp/bugs/browser/bugtarget.py", line 938, in similar_bugs
        matching_bugtasks = matching_bugtasks.prejoin([])
    ForbiddenAttribute: ('prejoin', <canonical.launchpad.components.decoratedresultset.DecoratedResultSet object at 0x12c46390>)
"

Then you've run into decoratedresultset not supporting prejoin.

I'm not sure that it should, as prejoin is a pretty fragile construction, but some points in LP disable prejoins lower layers establish (which has a number of problems), and if you add a DRS in between these points and the lower layer, security proxies will pop up and beat you on the head.

I'm going to set this as Opinion, and try searching for it, as I'm mainly writing this to help other folk encountering it.