Tukukkk

I am writing custom rules using SonarQube to scan properties and config files.
Can you please guide me how to write this custom code.

There is a plugin for java properties file https://github.com/racodond/sonar-jproperties-plugin. You can fork it and write your custom rules.
Here is an example rule wich checks for not allowed key and value combination

public class KeyValueCheck extends DoubleDispatchVisitorCheck {

    private static final String SIMPLE_IS_PATTERN_TEMPLATE = "(%s)";

    protected final Pattern patternKey;

    protected final Pattern patternValue;

    private final String VIOLATION_MESSAGE;

    private final boolean matches;

    boolean checkValue = false;



    public KeyValueCheck(String key, String value, String message, boolean matches) {

        VIOLATION_MESSAGE = message;

        this.matches = matches;

        this.patternKey = Pattern.compile(String.format(SIMPLE_IS_PATTERN_TEMPLATE, key), Pattern.CASE_INSENSITIVE);

        this.patternValue = Pattern.compile(String.format(SIMPLE_IS_PATTERN_TEMPLATE, value), Pattern.CASE_INSENSITIVE);

    }



    @Override

    public void visitKey(KeyTree tree) {

        Matcher matcher = patternKey.matcher(tree.text());

        if (matcher.matches()) {

            checkValue = true;

        }



        super.visitKey(tree);

    }



    @Override

    public void visitValue(ValueTree tree) {

        if (checkValue) {

            Matcher matcher = patternValue.matcher(tree.text());

            if (matches == patternValue.matcher(tree.text()).matches()) {

                addPreciseIssue(tree, VIOLATION_MESSAGE);

            }



            checkValue = false;

        }

        super.visitValue(tree);

    }

}