UnusedLocalVariable does not support local classes

[Vyom-Yadav]

I have read check documentation: https://checkstyle.sourceforge.io/checks/coding/unusedlocalvariable.html#UnusedLocalVariable
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

/var/tmp $ javac Test.java

/var/tmp $ cat config.xml

<?xml version="1.0"?>
<!DOCTYPE module PUBLIC "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
    "https://checkstyle.org/dtds/configuration_1_3.dtd">

<module name="Checker">
    <property name="charset" value="UTF-8" />
    <property name="severity" value="warning" />
    <property name="haltOnException" value="false" />
    <module name="TreeWalker">
        <module name="UnusedLocalVariable">
        </module>
    </module>
</module>

/var/tmp $ cat Test.java

public class Test {
    int a = 12;

    void foo() {
        int a = 12; // this is unused, no violation
        int ab = 12; // this is unused, violation thrown

        class asd {
            Test a = new Test() {
                void asd() {
                    System.out.println(a);
                }
            };
        }
    }
}

/var/tmp $ RUN_LOCALE="-Duser.language=en -Duser.country=US"
/var/tmp $ java $RUN_LOCALE -jar checkstyle-10.12.5-all.jar -c config.xml Test.java
Starting audit...
[WARN] /var/tmp/Test.java:6:9: Unused local variable 'ab'. [UnusedLocalVariable]
Audit done.

---

Describe what you expect in detail.

I expect a violation to be thrown for both the local variables. The check currently has no logic for scoping local classes, which is the root cause of this false negative. There might be cases where lack of this support might give a false positive.

[Vyom-Yadav]

Scoping local classes is difficult for the current check logic as local classes can have n nesting and their independent ecosystem. Local classes can extend other local classes, and all problems that occur with top-level classes can occur for local too. We currently don't do any scoping for local classes. Ideally, local classes should be tracked within the method boundary similar to top-level classes.

[Lmh-java]

Hi, is anyone working on this right now? If not, consider I am on it.