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 2733:

> 2731:                 try {
> 2732:                     scan(tree.body);
> 2733:                     for (int adr = forLoopVarMin; adr < forLoopVarMax; adr++) {

Question: since we already have a dedicated flag for loop variables - could we set the flag on _all_ loop variables (before the body), and then remove it in `letInit` (same as we do for effectively final flag) ? This way, at the end of the loop, the variables that still have the flag set will be the ones that have not been reassigned, correct?

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PR Review Comment: https://git.openjdk.org/jdk/pull/21415#discussion_r1793165126