Cleaning up CompileResult objects in test suite

[KRVPerera]

Due to the way testing works [1] many CompileResult object are kept in memory leading to OutOfMemoryError when running the test suite. See more details in original issue (closed) [2]

Based on a suggestion to clean them automatically seems the right approach but with some difficulties. See the below draft code. We cannot set any private object fields to null. Therefore finally we may have to search CompileResult object specifically and warn to issue exception if they are private. This may look like an unnecessary restriction to programmers. To reduce the hassle we can skip private check for primitive fields fieldType.isPrimitive().

Also JaCoCo introduce synthetic fields [3].

My code uses reflection. Why does it fail when I execute it with JaCoCo?
To collect execution data JaCoCo instruments the classes under test which adds two members to the classes: A private ? > static field $jacocoData and a private static method $jacocoInit(). Both members are marked as synthetic.
Please change your code to ignore synthetic members. This is a good practice anyways as also the Java compiler creates > synthetic members in certain situation.

package org.ballerinalang.test;

import org.testng.annotations.AfterClass;

import java.lang.reflect.Field;

public class BaseTest {

    protected boolean skipPrivateFields = true;
    protected boolean skipFinalFields = true;

    @AfterClass(alwaysRun = true)
    public void destroy() throws Exception {

        Class<?> compileResultClass = CompileResult.class;
        Class<?> compileResultUtilClass = org.ballerinalang.test.util.CompileResult.class;

        for (Field field : getClass().getDeclaredFields()) {
            /*
                To collect execution data JaCoCo instruments the classes under test which adds two members to the
                classes: A private static field $jacocoData and a private static method $jacocoInit(). Both members are
                marked as synthetic.
             */
            if (field.isSynthetic()) {
                continue;
            }
            var fieldType = field.getType();
            if (fieldType.isPrimitive()) {
                continue;
            }

            var fieldModifiers = field.getModifiers();
            boolean isPrivate = java.lang.reflect.Modifier.isPrivate(fieldModifiers);
            boolean isFinal = java.lang.reflect.Modifier.isFinal(fieldModifiers);

            boolean isCompileResult = fieldType.isAssignableFrom(compileResultClass) ||
                    fieldType.isAssignableFrom(compileResultUtilClass);

            if (isCompileResult) {
                /*
                    make sure to forcefully ask users to change `CompileResult` field modifiers to accessible ones
                 */
                if (!field.canAccess(this)) {
                    field.setAccessible(true);
                }
                if (isPrivate) {
                    throw new PrivateFieldException(field);
                }
                if (isFinal) {
                    throw new FinalFieldException(field);
                }
            }

            if (isPrivate) {
                if (skipPrivateFields) {
                    continue;
                }
                throw new PrivateFieldException(field);
            }

            if (isFinal) {
                if (skipFinalFields) {
                    continue;
                }
                throw new FinalFieldException(field);
            }

            if (field.get(this) != null) {
                field.set(this, null);
            }
        }
    }
}

...

[1] #27856 (comment)
[2] #27856
[3] https://www.jacoco.org/jacoco/trunk/doc/faq.html