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

[mahfouz72]

child of #14961

I have read check documentation:https://checkstyle.org/checks/coding/innerassignment.html#InnerAssignment
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="InnerAssignment">

        </module>
    </module>
</module>
➜  src cat Test.java                                
record ColoredPoint(int p, int x, String c) { }
record Rectangle(ColoredPoint upperLeft, ColoredPoint lowerRight) { }

public class Test {

    int test(Object obj) {
        int n;
        switch (obj) {
            case ColoredPoint(int x, int y, String z) when (x >= 2)
                    -> y = 6;
            default -> {
                n = 9;
            }
        };
        return switch (obj) {
            case ColoredPoint(int x, int y, String z) when (x >= 2)
                    -> y = 6;    // violation
            default -> {
                yield n = 9;     // violation
            }
        };
    }
}
➜  src javac --enable-preview --release 21 Test.java                        
➜  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:17:26: Inner assignments should be avoided. [InnerAssignment]
[ERROR] /home/nick/IdeaProjects/tester/src/Test.java:19:25: Inner assignments should be avoided. [InnerAssignment]
Audit done.
Checkstyle ends with 2 errors.

---

Describe what you want in detail

we are ok here. This was an issue that I fixed recently with this PR. So this can be closed

[nrmancuso]

Let's add a test input for this one (I don't see any record patterns or when expressions in the linked PR), @mahfouz72 can we make assignments in a when expressions?

[mahfouz72]

Nope

PS D:\CS\test> cat src/Test.java                                                
record ColoredPoint(boolean p, int x, int c) { }
record Rectangle(ColoredPoint upperLeft, ColoredPoint lowerRight) { }

public class Test {
    void test(Object obj) {
       boolean n = false;
        switch (obj) {
            case ColoredPoint(boolean x, int y, int c) when (n = true) -> {
                if (n = true) { }
            }
            case ColoredPoint(boolean x, int y, int c) when (x = true) -> {
                 if (x = true) { }
            }
            default -> { }
        }
    }
}
PS D:\CS\test> javac src/Test.java                                              
src\Test.java:8: error: cannot assign to n, as it was not declared inside the guard
            case ColoredPoint(boolean x, int y, int c) when (n = true) -> {
                                                             ^
src\Test.java:11: error: cannot assign to x, as it was not declared inside the guard
            case ColoredPoint(boolean x, int y, int c) when (x = true) -> {
                                                             ^
2 errors
PS D:\CS\test> 

[rnveach]

it was not declared inside the guard

Can you actually declare a variable inside the guard?

[rnveach]

@mahfouz72 Can you add an example of a switch expression?
Ex: int variable = switch (....

Edit: nevermind, this is probably the same as return switch .

[nrmancuso]

Updated the example now that we have added the EXPR token, we are good here.