Add Check Support for Java 21 Pattern Matching for Switch Syntax: CyclomaticComplexity

[mahfouz72]

child of #14961

I have read check documentation:https://checkstyle.org/checks/metrics/cyclomaticcomplexity.html
I have downloaded the latest checkstyle from: https://checkstyle.org/cmdline.html#Download_and_Run
I have executed the cli and showed it below, as cli describes the problem better than 1,000 words

---

➜  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="CyclomaticComplexity">
            <property name="max" value="3"/>
        </module>
    </module>
</module>
➜  src cat Test.java                                
import java.awt.color.ICC_ColorSpace;

record ColoredPoint(int p, int x, boolean c) {
}
record Rectangle(ColoredPoint upperLeft, ColoredPoint lowerRight) {
}

public class Test {

    // violation,  Cyclomatic Complexity is 4
    void test(Object obj) {  // 1, function declaration
        switch (obj) {
            case ColoredPoint(int a, int b, _)  // 2 , case
                    when (a >= b) -> {        // should we add 1 for when ? it was literally a `&&` before
            }
            case ColoredPoint(int a, int b, _) -> {}  // 3, case
            case Rectangle(_, _) -> {}  // 4, case
            default -> System.out.println("none");
        }
    }

    // violation,  Cyclomatic Complexity is 5
    void test2(Object obj) {  // 1, function declaration
        // I interpreted `when` as `&&`
        if (obj instanceof ColoredPoint(int a, int b, _) && a >= b) { // 2, if and 3, '&&'

        } else if (obj instanceof ColoredPoint(int a, int b, _)) { // 4 if

        } else if (obj instanceof Rectangle(_, _)) {   // 5 if

        }
    }
}
➜  src javac --enable-preview --release 21 Test.java
Note: Test.java uses preview features of Java SE 21.
Note: Recompile with -Xlint:preview for details.
➜  src java -jar checkstyle-10.18.1-SNAPSHOT-all.jar -c config.xml Test.java
Starting audit...
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:11:5: Cyclomatic Complexity is 4 (max allowed is 3). [CyclomaticComplexity]
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:23:5: Cyclomatic Complexity is 5 (max allowed is 3). [CyclomaticComplexity]
Audit done.
Checkstyle ends with 2 errors.

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Describe what you want in detail

Since we add 1 for &&. I think it makes sense that when should be considered as +1 here. It is just the same as && in if conditions see the similarities between the two examples

[nrmancuso]

We will add support for https://checkstyle.sourceforge.io/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#LITERAL_WHEN as a default token, and count this token as +1 as recommended by @mahfouz72 .

I am approving this issue.

[nrmancuso]

Ok, I have updated the OP, result is the same as before we had a nested EXPR token. Re-approving for same conditions from #15045 (comment)