RFR: 8244413: Avoid rebinds in MethodHandle.viewAsType

[Mandy Chung]

On 5/5/20 3:12 PM, Claes Redestad wrote:
> Hi,
>
> in the current implementation MethodHandle.viewAsType eagerly rebinds
> when creating a view of a method type as an alternative type:
>
>     MethodHandle viewAsType(MethodType newType, boolean strict) {
>         ...
>         MethodHandle mh = rebind();
>         return this.copyWith(newType, mh.form);
>     }
>
> This prevents exposing uncrackable DMHs, ie, ones where calling
> Lookup.revealDirect(mh) would not produce a correct MethodHandleInfo.
>
> If we restructure this so that crackability is a property on the DMH, we
> can avoid the rebinds:
>
> http://cr.openjdk.java.net/~redestad/8244413/open.00/
>

This looks good.

Nit: one assert with paratheses and the other without.  Better to make 
them consistent.

163 assert viewAsTypeChecks(newType, strict);  164 
assert(this.getClass() == DirectMethodHandle.class); // must override in 
subclasses


thanks
Mandy