RFR: 8341782: Allow lamba capture of basic for() loop variables as with enhanced for()

[Maurizio Cimadamore]

On Tue, 8 Oct 2024 19:53:56 GMT, Archie Cobbs <acobbs at openjdk.org> wrote:

> This PR changes the compiler to allow basic `for()` loop iteration variables to be captured by lambdas in the loop body, even when their "effectively final" status is invalidated by modifications in the header of the loop.
> 
> This allows code like this to compile:
> 
> for (int i = 1; i <= 3; i++) {
>     Runnable r = () -> System.out.println(i);
> }

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 2729:

> 2727:                     uninitsSkip.inclRange(firstadr, nextadr);
> 2728:                 }
> 2729:                 final Bits reassignedInForLoopBodyPrev = reassignedInForLoopBody;

My memory of this code is a bit rusty, so please bear with me... I seem to recall we mark all variables as effectively final, and then "unmark" them if see see them in `letInit`. If this is correct, could we simply re-force the effectively final flag of a loop variable before the loop body?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/21415#discussion_r1792523413