RFR: 8294943: Implement record patterns in enhanced for [v11]

Aggelos Biboudis abimpoudis at openjdk.org
Tue Nov 15 18:26:45 UTC 2022

> This PR enables the ability to use record patterns in the enhanced-for, initializing the record components accordingly: 
> record Complex(double real, double img) {}
> List<Complex> list = ...;
> for (Complex(var real, var img) : list) {
>     // can use “real” and “img” directly
> }
> This PR proposes an implementation for the "Record Patterns in Enhanced For" [subtask](https://bugs.openjdk.org/browse/JDK-8294943) regarding the following [CSR](https://bugs.openjdk.org/browse/JDK-8294944) (note the different JBS entries), summarised by the following:
> - It enhances the grammar for the `EnhancedForStatement` to support record patterns too, alongside `LocalVariableDeclarations`.
> - Any pattern variables introduced by the record pattern in the header of the pattern are definitely matched in the statement block of the enhanced for. 
> - The record patterns are only permitted when the pattern is exhaustive over the enhanced for's expression.
> - In the case that the element of the iteration is `null`, the switch raises a `MatchException` wrapping the `NullPointerException`.
> - The enhanced for, supports record patterns for both arrays and reference types.
> Currently, the precise meaning of the enhanced for statement is given by translation into a basic for statement. By introducing record patterns in the pattern header, the new meaning is defined by the new translation which incorporates a switch whose selector expression is the enhanced for's expression, and whose singleton case has the given record pattern as a sole label would be exhaustive. Note, that in cases where the imaginary switch would reach the default clause and end abruptly, the enhanced for each will end abruptly for the same reason.
> For more information on the changes please see:
> - the JEP: [JEP 432](https://openjdk.org/jeps/432) 
> - the CSR: [JEP 432 - JDK-8294944](https://bugs.openjdk.org/browse/JDK-8294944) 
> - 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) 
> Looking forward for your review.

Aggelos Biboudis has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 18 commits:

 - Improve error message on non-exhaustive enhanced for
 - Merge branch 'JDK-8294942' into for-patterns
   # Conflicts:
   #	test/langtools/tools/javac/patterns/GenericRecordDeconstructionPattern.java
 - Cleanup
 - Fix parsing error in presence of lambdas
 - Fix parsing error in presence of nested patterns
 - Merge pull request #1 from lahodaj/for-patterns
   Fixing record patterns with primitive components in enhanced for
 - Cleanup
 - Fixing pattern/non-pattern disambiguation in presence of primitive-typed patterns.
 - Address review
 - Simplify getDeclarationKind
 - ... and 8 more: https://git.openjdk.org/jdk/compare/5afc6023...42f0cecb


Changes: https://git.openjdk.org/jdk/pull/10798/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=10798&range=10
  Stats: 744 lines in 26 files changed: 674 ins; 7 del; 63 mod
  Patch: https://git.openjdk.org/jdk/pull/10798.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10798/head:pull/10798

PR: https://git.openjdk.org/jdk/pull/10798

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