Fix Parameter Runtime*ParameterAnnotations spec

[Alex Buckley]

On 10/31/2017 1:47 AM, Remi Forax wrote:
> Hi all, the spec of the Runtime*ParameterAnnotations attribute [1],
> allow the number of parameter annotations to be different from the
> number of parameter from the method descriptor but it fails to
> provide a way to retrieve/compute the mapping between a parameter and
> a parameter annotation.
>
> So people try to guess and fail, here is by example the ASM bug when
> we tried to provide such mapping to our user [2].
>
> We (the ASM team) believe the only way to fix that is to require that
> if the number of parameters from the descriptor and the number of
> parameter annotations doesn't match then compilers should also emit a
> Parameter attribute which already indicate if a parameter is
> synthetic or not.

I recognize that constructor parameters are a painful cause of 
discrepancy between the method descriptor and various attributes -- not 
just Runtime*ParameterAnnotations but also Signature (see the note "A 
method signature encoded by ..." in 
https://docs.oracle.com/javase/specs/jvms/se9/html/jvms-4.html#jvms-4.7.9.1).

However, the decision in JDK-8067975 was to loosen the JVMS' description 
so that it admitted the class files emitted by javac and ecj. If you 
want javac and ecj to emit something different than they do today, then 
your best bet is to write up a "State of the Parameters" page that shows 
the "interesting" programs, and what javac and ecj emit. Only then can 
suggestions like "Emit a MethodParameters attribute if ..." be evaluated.

Alex