RFR: 8294942: Compiler implementation for Record Patterns (Second Preview)

[Aggelos Biboudis]

On Fri, 21 Oct 2022 11:56:50 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

> This is a partial implementation of [JEP 432: Record Patterns (Second Preview)](https://openjdk.org/jeps/432) and [JEP 433: Pattern Matching for switch (Fourth Preview)](https://openjdk.org/jeps/433). Namely, it implements:
> 
>  - removal of named record patterns
>  - (preview) type inference for type test and record patterns
>  - cleaner switch case specification (e.g. no combination of `null` constants and type test patterns)
>  - fixing exhaustiveness of certain switches
> 
> The patch does not contain support for record patterns in enhanced for statements, that is [part of a separate pull request](https://github.com/openjdk/jdk/pull/10798).
> 
> For more information on the changes please see:
>  - the JEPs: [JEP 432](https://openjdk.org/jeps/432) and [JEP 433](https://openjdk.org/jeps/433)
>  - the CSRs: [JEP 432 - JDK-8294944](https://bugs.openjdk.org/browse/JDK-8294944) and [JEP 433 - JDK-8294946](https://bugs.openjdk.org/browse/JDK-8294946)
>  - the current [specification draft](https://cr.openjdk.java.net/~gbierman/jep432%2b433/jep432+433-20221018/specs/patterns-switch-record-patterns-jls.html#jls-14.14.2) (note the draft does not yet include details on type inference)
> 
> Any feedback is welcome.
> 
> Thanks!

Some minor comments.

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Infer.java line 656:

> 654:     }
> 655: 
> 656:     public Type instantiatePatternType(DiagnosticPosition pos, Type expressionType, TypeSymbol patternTypeSymbol) {

`pos` seems unused so far.

test/langtools/tools/javac/patterns/NewCaseStructureTest.java line 283:

> 281:                            case Integer i when i > 0 -> 0;
> 282:                            case 0 -> 0;
> 283:                            case Integer i -> 0;

This case is not needed, right?

test/langtools/tools/javac/patterns/NewCaseStructureTest.java line 299:

> 297:                            case E e when e == E.A -> 0;
> 298:                            case B -> 0;
> 299:                            case E e -> 0;

Similarly.

test/langtools/tools/javac/patterns/NewCaseStructureTest.java line 316:

> 314:                            case String s when s.isEmpty() -> 0;
> 315:                            case "a" -> 0;
> 316:                            case String s -> 0;

Similarly.

test/langtools/tools/javac/patterns/NewCaseStructureTest.java line 348:

> 346:                            default -> 0;
> 347:                            case (Integer i) when i > 0 -> 0;
> 348:                            case (Integer i) when i > 0 -> 0;

Similarly.

test/langtools/tools/javac/patterns/NewCaseStructureTest.java line 361:

> 359:                    private int test(Integer o) {
> 360:                        return switch (o) {
> 361:                            case (Integer i) when i > 0 -> 0;

Similarly.

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PR: https://git.openjdk.org/jdk/pull/10814