RFR: 8262889: Compiler implementation for Record Patterns

[Maurizio Cimadamore]

On Tue, 3 May 2022 12:07:50 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.

I've added some renaming suggestions for the code in Flow, after some discussions with @biboudis.
More generally, that code should contain comments, with example of what it's trying to do - e.g. how it's partitioning the set of patterns, etc.

src/java.base/share/classes/jdk/internal/javac/PreviewFeature.java line 64:

> 62:     public enum Feature {
> 63:         SWITCH_PATTERN_MATCHING,
> 64:         DECONSTRUCTION_PATTERNS,

The spec and JEP talks about record patterns - I think we should follow the correct name here

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 751:

> 749:                                            Iterable<? extends JCCaseLabel> labels) {
> 750:             Set<Symbol> constants = new HashSet<>();
> 751:             Map<Symbol, List<JCDeconstructionPattern>> categorizedDeconstructionPatterns = new HashMap<>();

maybe rename to `deconstructionPatternsBySymbol` ?

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 790:

> 788:         }
> 789: 
> 790:         private boolean coversDeconstructionStartingFromComponent(DiagnosticPosition pos,

maybe rename as `coverDeconstructionFromComponent`/`coverDeconstructionAt`

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 792:

> 790:         private boolean coversDeconstructionStartingFromComponent(DiagnosticPosition pos,
> 791:                                                                   Type targetType,
> 792:                                                                   List<JCDeconstructionPattern> patterns,

patterns -> "deconstructionPatterns"

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 800:

> 798:             }
> 799: 
> 800:             Type parameterizedComponentType = types.memberType(targetType, components.get(component));

maybe `instantiatedComponentType`

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 802:

> 800:             Type parameterizedComponentType = types.memberType(targetType, components.get(component));
> 801:             List<JCPattern> nestedComponentPatterns = patterns.map(d -> d.nested.get(component));
> 802:             Set<Symbol> nestedCovered = coveredSymbols(pos, parameterizedComponentType,

maybe `coveredComponents`

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 807:

> 805:             Set<Symbol> covered = new HashSet<>();
> 806: 
> 807:             for (JCDeconstructionPattern subTypeCandidate : patterns) {

`subTypeCandidate` -> `deconstructionPattern`

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 809:

> 807:             for (JCDeconstructionPattern subTypeCandidate : patterns) {
> 808:                 JCPattern nestedPattern = subTypeCandidate.nested.get(component);
> 809:                 Symbol currentPatternType;

`currentPatternType` -> `componentPatternType`

src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 823:

> 821:                     }
> 822:                 }
> 823:                 for (Symbol currentType : nestedCovered) {

`currentType` -> `coveredComponent`

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/JCTree.java line 246:

> 244:         PARENTHESIZEDPATTERN,
> 245: 
> 246:         DECONSTRUCTIONPATTERN,

might want to rename to RECORDPATTERN (but this is impl dependent, so less important to fix)

src/jdk.compiler/share/classes/com/sun/tools/javac/tree/JCTree.java line 2373:

> 2371:     }
> 2372: 
> 2373:     public static class JCDeconstructionPattern extends JCPattern

JCRecordPattern (although this is impl-only, so less important to fix)

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