[code-reflection] RFR: Simplify code generation for quotable lambdas not to require duplicate capture argument lists [v2]

[Paul Sandoz]

On Mon, 7 Oct 2024 12:43:26 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> When translating quotable lambdas/method references, we generate two captured argument lists:
>> 
>> * the captured arguments to be used by the functional interface implementation;
>> * the captured arguments to be used by the quotable implementation
>> 
>> In most cases these two captured lists are identical, except for cosmetic differences.
>> This is even more true after the backend of javac underwent significant rearchitecture, to better support the Flexible Constructor Bodies feature.
>> 
>> This PR simplifies `ReflectMethods` so that a visitor now computes all the required captured variables upfront.
>> The captured variables are then inserted in the quoted block, so that the rest of `BodyScanner` will be able to resolve references to such variables w/o the need for ad-hoc logic.
>> 
>> One complication is that, under this new regime, we can no longer afford to treat captured variables whose value is constant (e.g. `final int k = 100`) as if they were true captures.
>> This is because neither `Lower` nor `LambdaToMethod` capture constant variables. Since we're reusing the same dynamic arguments as `LambdaToMethod` we need to make sure that `ReflectMethods` also does not capture constant arguments.
>> Special logic to avoid capture of constant arguments is baked into the new visitor.
>> 
>> I have also added a check in the visitor, so that if, inside a quotable lambda, we see a creation of a local class that is declared outside the lambda, an unsupported exception is thrown.
>> 
>> I will followup with a separate fix to deal with these cases.
>
> Maurizio Cimadamore has updated the pull request incrementally with three additional commits since the last revision:
> 
>  - Update src/jdk.compiler/share/classes/com/sun/tools/javac/comp/ReflectMethods.java
>    
>    Co-authored-by: Paul Sandoz <paul.d.sandoz at googlemail.com>
>  - Address review comments
>  - Drop spurious reference to `LambdaToMethod`

Marked as reviewed by psandoz (Lead).

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PR Review: https://git.openjdk.org/babylon/pull/249#pullrequestreview-2352259025