Add Check Support for Java 21 Unnamed Variables & Patterns Syntax: MagicNumber about checkstyle HOT 8 OPEN

Please add an example of a pattern as well.

I am good to add an input.

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I don't get it. we can't declare a pattern with a magic number. The pattern is being matched only can you share example?

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Sorry, patterns can't have numbers directly assigned to them. They are just type and variable name. I believe I was trying to say this issue didn't mention patterns at all, and patterns can have whens. This might be another issue, but did we try this check with when on patterns?

from checkstyle.

This check is fine on patterns with a when guard:

➜  src javac Test.java
➜  src cat Test.java  
public class Test {
    public static void main(String[] args) {

       Object o = new Object();

        if (o instanceof Integer i && i < 3) { // violation
            System.out.println("null");
        } else {
            System.out.println("not null");
        }

        switch (o) {
            case Integer i when i < 3: // violation
                System.out.println("null");
                break;
            default:
                System.out.println("not null");
        }
    }
}
➜  src cat config.xml 
<?xml version="1.0"?>
<!DOCTYPE module PUBLIC
        "-//Puppy Crawl//DTD Check Configuration 1.3//EN"
        "http://www.puppycrawl.com/dtds/configuration_1_3.dtd">
<module name="Checker">
    <property name="charset" value="UTF-8"/>
    <module name="TreeWalker">
        <module name="MagicNumber">
        </module>
    </module>
</module>
➜  src java -jar checkstyle-10.17.0-all.jar -c config.xml Test.java
Starting audit...
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:6:43: '3' is a magic number. [MagicNumber]
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:13:37: '3' is a magic number. [MagicNumber]
Audit done.
Checkstyle ends with 2 errors.

@mahfouz72 do we have an issue for this one?

This check will not apply to unnamed patterns at all, since _ can never be referenced (therefore we cannot use it in a when guard where we would have some conditional).

from checkstyle.

do we have an issue for this one?

the things related to when only should be covered in the pattern matching for switch syntax tracker. this syntax is not related to unnamed patterns. But the list of the checks there doesn't have MagicNumberCheck. So, No we don't have an issue with this syntax for this check. do you think we should open one for an input file only (the behavior is correct)?

This check will not apply to unnamed patterns at all, since _ can never be referenced (therefore we cannot use it in a when guard where we would have some conditional).

then I think we can close this

from checkstyle.

the things related to when only should be covered in the pattern matching for switch syntax tracker

#14961

do you think we should open one for an input file only (the behavior is correct)?

I am good with this.

then I think we can close this

@nrmancuso

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#15107

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Approved for test inputs

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