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From: Ethan Jucovy <ethan.jucovy@gmail.com>
Date: Wed, 4 Apr 2012 12:43:48 -0400
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 <CAMmgw9=_+B14ciKPH68AbGhnDG8zFSHsQ5b-rxNBa1ssgKG2ug@mail.gmail.com>
Subject: Re: [Apache Bloodhound] #22: Infinite recursion error when
 initialising a plugin that extends itself
To: bloodhound-dev@incubator.apache.org
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>
>  [
> http://svn.apache.org/viewvc/incubator/bloodhound/trunk/trac/trac/core.py?view=diff&r1=1309469&r2=1309470&pathrev=1309470
>  r1309470] fixes by dynamically replacing the __init__ of components with
>  one that runs the original __init__ on the condition that it has not
>  already been run.
>
>  I suspect what would be better in the long run would be to catch the
>  recursion error and turn it into something that can be reported but allows
>  Bloodhound to continue working. Plugins should probably keep track of
>  whether an instance has already been initialised.


This issue was raised on trac-dev[1].  It was pointed out that the
ThemeEngine plugin is incorrectly accessing its extension points in
__init__, which it should not do:

"A component constructor is called in a
special way, as you've found out, and it should really do pretty
much nothing.  Example of valid use is to set a list to [], a
hash to {}, or such.  In trunk you could even use @lazy
(http://trac.edgewall.org/changeset/10737) to help with such
things. So doing anything lengthy is prohibited and the same
for "re-entering" the component machinery."

Perhaps Trac core should be throwing a more helpful error than infinite
recursion, but the correct fix here is to make ThemeEngineSystem.__init__
do less (e.g. ``self._info = None``) and populate its ``self.info`` dict
lazily.  There's no need for this __init__-replacing magic in core.

[1]
http://old.nabble.com/Create-new-ticket-vs-reopen--9418-(if-necessary--)-td33164546.html

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