Additional -Xlint:serial warning

[Florian Weimer]

* Neal Gafter:

> Unfortunately, many inner classes are only "incidentally" serializable -
> that is, they are serializable because the superclass or some implemented
> interface extends Serializable.  A simple example would be an inner
> exception class - even though most programs do not serialize exceptions,
> this would trigger the proposed diagnostic.

Inner exception classes probably should be non-static.  And many
incidentally serializable classes already receive a warning under
-Xlint due to a missing serialVersionUID field.

If necessary, the warning could be restricted to classes with a
declared serialVersionUID member, or class definitions explicitly
implementing the Serializable interface.

(I spent a few hours hunting down a bug caused by a mismatch between
this$0 and this$1, that's why I think something should be done about
it.)

-- 
Florian Weimer                <fweimer at bfk.de>
BFK edv-consulting GmbH       http://www.bfk.de/
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