RFR: 8262889: Compiler implementation for Record Patterns [v3]

Maurizio Cimadamore mcimadamore at openjdk.java.net
Mon May 9 08:20:58 UTC 2022

On Sat, 7 May 2022 12:03:04 GMT, Jan Lahoda <jlahoda at openjdk.org> wrote:

>> 8262889: Compiler implementation for Record Patterns
>> A first version of a patch that introduces record patterns into javac as a preview feature. For the specification, please see:
>> http://cr.openjdk.java.net/~gbierman/jep427+405/jep427+405-20220426/specs/patterns-switch-record-patterns-jls.html
>> There are two notable tricky parts:
>> -in the parser, it was necessary to improve the `analyzePattern` method to handle nested/record patterns, while still keeping error recovery reasonable
>> -in the `TransPatterns`, the desugaring of the record patterns is very straightforward - effectivelly the record patterns are desugared into guards/conditions. This will likely be improved in some future version/preview
>> `MatchException` has been extended to cover additional cases related to record patterns.
> Jan Lahoda has updated the pull request incrementally with two additional commits since the last revision:
>  - Fixing guards after record patterns.
>  - Raw types are not allowed in record patterns.

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Attr.java line 4208:

> 4206:         if (site.tsym.kind == Kind.TYP && ((ClassSymbol) site.tsym).isRecord()) {
> 4207:             ClassSymbol record = (ClassSymbol) site.tsym;
> 4208:             if (record.type.getTypeArguments().nonEmpty()) {

There is a `Type::isRaw()` - I supposed you tried that one? Doesn't it do what you want?

test/langtools/tools/javac/patterns/DeconstructionPatternErrors.out line 3:

> 1: DeconstructionPatternErrors.java:15:28: compiler.err.underscore.as.identifier
> 2: DeconstructionPatternErrors.java:15:29: compiler.err.expected: token.identifier
> 3: DeconstructionPatternErrors.java:43:37: compiler.err.illegal.start.of.type

should error be more specific here? E.g. diamond not supported with type test pattern?


PR: https://git.openjdk.java.net/jdk/pull/8516

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