RFR: 8372635: Lambdas do not copy over SYNTHETIC flag for local variables [v2]

[Chen Liang]

On Thu, 11 Dec 2025 13:58:28 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> Consider case like:
>> 
>> Object o = ...;
>> 
>> //synthetic variable for the instanceof's expression
>> boolean b = o.toString() instanceof String str && str.isEmpty();
>> 
>> Runnable r = () -> {
>>         //synthetic variable for the instanceof's expression
>>         boolean b = o.toString() instanceof String str && str.isEmpty();
>> };
>> 
>> 
>> There are synthetic variables generated for `o.toString()`, to ensure the method is invoked only once for each `instanceof`. These variables are marked as synthetic in `TransPatterns` (and then consequently omitted in `LocalVariableTable`), but when the flag is lost for the variable in the lambda.
>> 
>> This PR proposes to keep the flag, as suggested in the bug.
>
> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Copy all flags when creating lambda local var/parameter.

Lgtm assuming there is no test failure

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Marked as reviewed by liach (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/28724#pullrequestreview-3568730903