Review request: update javac to properly output mandated parameters in MethodParameters attributes

[Alex Buckley]

On 2/12/2013 10:22 PM, John Rose wrote:
> On Feb 12, 2013, at 5:50 PM, Alex Buckley <alex.buckley at oracle.com
> <mailto:alex.buckley at oracle.com>> wrote:
>
>> Per the new discussion in JLS 8.8.9 which appears in 8misc.pdf, it is
>> possible for a _non-private_ inner member class to be instantiated by
>> code in a totally different compilation unit, _compiled by a different
>> compiler than compiled the inner member class_.
>
> Since even private member classes have mandated names, it is possible to
> use reflection (with access control overrides as needed) to attempt to
> instantiate even private member classes.  This suggests to me that
> 'private' might not be enough isolation to allow complete freedom to the
> compiler.
>
> On the other hand, non-member classes (anonymous and locals) do not have
> mandated bytecode names (there is always a $[0-9]+ component in the
> name), so it is reasonable to say none of the constructors and/or
> arguments need to have any mandated structure.
>
> I realize that the JLS is one step away from reflective APIs, but there
> is a logical connection here, since the Core Reflection API claims to be
> able to (a) replicate legal member accesses, and (b) override access
> protection modifiers ('private' etc.).
>
>> Hence the mandated parameter which allows all compilers to reify the
>> immediately enclosing instance. But a _private_ inner member class can
>> only be instantiated within the same compilation unit, so it's the
>> compiler's choice how to reify the immediately enclosing instance in
>> that case, and I believe javac has always used ACC_SYNTHETIC for that
>> class's default ctor.
>
> It's always used ACC_SYNTHETIC but that doesn't mean that ACC_MANDATED
> would be better for some bits of the puzzle.

It would be pleasant to treat private and non-private ctors of member 
classes the same, but as a practical matter, I don't know that all Java 
compilers even use a ctor parameter to pass 
immediately-enclosing-instance for a private member class. For a 
non-private member class, I am happier to assume that all Java compilers 
followed javac and that new JLS text is relatively harmless.

I added a note to the new 8.8.9 that the mandating of ctor parameters 
for member classes v. local/anonymous classes mirrors the mandating of 
predictable v. non-predictable binary names in 13.1 - thanks for 
reminding me of that link.

> P.S. Do we still mandate names of certain inner class fields, such as
> 'this$NNN'?  The original motivation for this was to allow debuggers a
> somewhat easier time presenting compiler-generated data structures.

The JLS has never done this, so I don't know who would be mandating it.

Alex