[code-reflection] RFR: Drop support for quoted structural lambdas [v2]

[Paul Sandoz]

On Thu, 6 Nov 2025 15:29:20 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> The Babylon compiler extension supports structural quoting of lambdas. That is, if a lambda expression has `Quoted` target, then it must have explicit parameter types, and must be type-checked bottom up:
>> 
>> 
>> Quoted q = () ->  {}
>> 
>> 
>> Historically, `Quoted` was the first way to model quotable lambda expressions, and the language changes to support structural quotable lambdas were fairly invasive. Since then we moved to a more minimalistic approach which is similar to what we do for serializable lambdas: we use an intersection type cast to force quotability of the lambda expression:
>> 
>> 
>> Runnable r = (Runnable & Quotable)() ->  {}
>> 
>> 
>> Since the surface area of the `Quotable` support is much smaller (it shares the same machinery already available for serializable lambdas), it would be better to remove support for Quoted target when moving towards incubation.
>> 
>> This PR fixes all existing tests in langtools/JDK to use `Quotable` instead of `Quoted`. I did **not** check HAT, or `cr-examples`.
>
> Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Re-add accidentally deleted test

Very good! Really simplifies things.

The examples and HAT do not target lambda expressions to `Quoted`, so no updates required.

To support targeting to `Quoted` we had to add `ClosureOp` and `ClosureCallOp`. We could also remove these too, and their use in the interpreter (the byte code generator never used them).

test/jdk/java/lang/reflect/code/bytecode/TestQuoted.java line 49:

> 47:     @Test
> 48:     public void testQuoted() throws Throwable {
> 49:         Quotable q = (IntBinaryOperator & Quotable)(int i, int j) -> {

We can delete this test, as there are others testing lambda expressions.

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

PR Review: https://git.openjdk.org/babylon/pull/667#pullrequestreview-3429706209
PR Review Comment: https://git.openjdk.org/babylon/pull/667#discussion_r2500178383