8348928: Check for case label validity are misbehaving when binding patterns with unnamed bindings are present

[lahodaj]

Consider code like:

public class Exp0 {
    public static void main(String... args) {
        Object o = "";
        record R(int i, String s) {}

        switch (o) {
            case Integer _, R(int i, String _) -> {}
            default -> {}
        }
    }
}

This compiles OK, but it shouldn't. The JLS says:

It is a compile-time error for a case label to have more than one case pattern and declare any pattern variables (other than those declared by a guard associated with the case label).

Some similar cases leads to a javac crash:

$ cat Exp2.java 
public class Exp2 {
    public static void main(String... args) {
        Object o = "";
        record R(int i, String s) {}

        switch (o) {
            case Integer _:
            case R(int i, String _):
                System.err.println(i);
                break;
            default: break;
        }
    }
}

$ jdk-24/bin/javac Exp2.java
An exception has occurred in the compiler (24-internal). Please file a bug against the Java compiler via the Java bug reporting page (https://bugreport.java.com) after checking the Bug Database (https://bugs.java.com) for duplicates. Include your program, the following diagnostic, and the parameters passed to the Java compiler in your report. Thank you.
java.lang.AssertionError
        at jdk.compiler/com.sun.tools.javac.util.Assert.error(Assert.java:155)
        at jdk.compiler/com.sun.tools.javac.util.Assert.check(Assert.java:46)
        at jdk.compiler/com.sun.tools.javac.jvm.Items$LocalItem.<init>(Items.java:392)
        at jdk.compiler/com.sun.tools.javac.jvm.Items.makeLocalItem(Items.java:133)
        at jdk.compiler/com.sun.tools.javac.jvm.Gen.visitIdent(Gen.java:2350)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCIdent.accept(JCTree.java:2711)
...
printing javac parameters to: /tmp/javac.20250321_150757.args

The root cause here is a bug when determining whether or not a given case label contains bindings - the "has-bindings" flag gets cleared when _ is used. The "has-bindings" flags must remain set despite seeing unnamed binding variables.

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change requires CSR request JDK-8348933 to be approved

Issues

• JDK-8348928: Check for case label validity are misbehaving when binding patterns with unnamed bindings are present (Bug - P3)
• JDK-8348933: Check for case label validity are misbehaving when binding patterns with unnamed bindings are present (CSR)

Reviewers

• Adam Sotona (@asotona - Reviewer)
• Aggelos Biboudis (@biboudis - Reviewer)
• Vicente Romero (@vicente-romero-oracle - Reviewer)

Reviewing

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[bridgekeeper]

👋 Welcome back jlahoda! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

@lahodaj This change now passes all automated pre-integration checks.

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After integration, the commit message for the final commit will be:

8348928: Check for case label validity are misbehaving when binding patterns with unnamed bindings are present

Reviewed-by: asotona, abimpoudis, vromero

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At the time when this comment was updated there had been 575 new commits pushed to the master branch:

• cc9148d: 8354695: Open source several swing tests batch7
• 1b8f760: 8354928: Clean up and open source some miscellaneous AWT tests
• 239760a: 8355233: Add a DMB related benchmark
• ... and 572 more: https://git.openjdk.org/jdk/compare/b025d8c2e062210b6148da43f11517666b0b4932...master

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[mlbridge]

Webrevs

• 00: Full (888e87b9)

[asotona]

Looks good to me.

[biboudis]

Seems good.

[vicente-romero-oracle]

lgtm

[lahodaj]

/integrate

[openjdk]

Going to push as commit 7bfbb9a.
Since your change was applied there have been 616 commits pushed to the master branch:

• 188c236: 8353558: x86: Use better instructions for ICache sync when available
• 428334b: 8353216: Improve VerifyMethodHandles for method handle linkers
• bbec3c0: 8354558: -XX:AOTMode=record crashes with boot loader package-info class
• ... and 613 more: https://git.openjdk.org/jdk/compare/b025d8c2e062210b6148da43f11517666b0b4932...master

Your commit was automatically rebased without conflicts.

[openjdk]

@lahodaj Pushed as commit 7bfbb9a.

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