RFR 8169345: javac crash when local from enclosing context is captured multiple times

[Vicente Romero]

Looks good,

Thanks,
Vicente

On 10/06/2017 10:39 AM, Maurizio Cimadamore wrote:
> Hi,
> this patch fixes an issue regarding how Lower handles captured 
> variables from enclosing scopes. Quoting from my analysis in JBS [1]:
>
> class Main {
>     void test () {
>         Object o = new Object();
>         class Local1 {
>             Object test1() { return o; }
>         }
>         class Local2 {
>              void test2() {
>                   Object o = new Object();
>                   class Local3 extends Local1 {
>                       Object test3() { return o; }
>                    }
>              }
>         }
>     }
> }
>
> Here, class Local3 captures 'o' from:
>
> * Main::test (this capture is necessary, as the superclass constructor 
> (for Local1) will need to take that 'b'
> * Local2::test2 (this capture is necessary as that's the variable 
> referenced to by the Local3::test3 method)
>
> This ends up breaking many invariants inside Lower, as:
>
> * Lower represents all captured variables using a simple encoding such 
> as 'val' $ 'varname' - meaning that both captured variables above end 
> up as 'val$o'. This will cause issues when looking up the variable - 
> which is currently done with a named scope lookup (find first).
>
> * Lower.initField assumes that there's only one (synthetic) parameter 
> named 'val$o' in the lowered constructor declaration and it also 
> assumes that there's only one (synthetic) field in the local with the 
> same name. This correspondency allows Lower to generate the synthetic 
> field initializer by relying on scope properties.
>
>
> Here's the webrev:
>
> http://cr.openjdk.java.net/~mcimadamore/8169345/
>
> Note - this has been briefly discussed in [2].
>
> Cheers
> Maurizio
>
> [1] - https://bugs.openjdk.java.net/browse/JDK-8169345
> [2] - 
> http://mail.openjdk.java.net/pipermail/compiler-dev/2017-February/010790.html
>
>