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8348928: Check for case label validity are misbehaving when binding patterns with unnamed bindings are present #24155

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lahodaj
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@lahodaj lahodaj commented Mar 21, 2025

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)

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bridgekeeper bot commented Mar 21, 2025

👋 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.

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

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

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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@openjdk openjdk bot added csr Pull request needs approved CSR before integration rfr Pull request is ready for review labels Mar 21, 2025
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@lahodaj The following label will be automatically applied to this pull request:

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When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

@openjdk openjdk bot added the compiler compiler-dev@openjdk.org label Mar 21, 2025
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mlbridge bot commented Mar 21, 2025

Webrevs

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@asotona asotona left a comment

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Looks good to me.

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@biboudis biboudis left a comment

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Seems good.

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@vicente-romero-oracle vicente-romero-oracle left a comment

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lgtm

@openjdk openjdk bot added ready Pull request is ready to be integrated and removed csr Pull request needs approved CSR before integration labels Apr 22, 2025
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lahodaj commented Apr 24, 2025

/integrate

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openjdk bot commented Apr 24, 2025

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

Your commit was automatically rebased without conflicts.

@openjdk openjdk bot added the integrated Pull request has been integrated label Apr 24, 2025
@openjdk openjdk bot closed this Apr 24, 2025
@openjdk openjdk bot removed ready Pull request is ready to be integrated rfr Pull request is ready for review labels Apr 24, 2025
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openjdk bot commented Apr 24, 2025

@lahodaj Pushed as commit 7bfbb9a.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.

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4 participants