A DESCRIPTION OF THE PROBLEM :
Complete summary: "Matcher.hitEnd returns false for incomplete surrogate pairs after matches() and lookingAt()"

When using a Matcher for an incomplete surrogate pair as input, Matcher.hitEnd() returns false after matches() or lookingAt(). Interestingly using it after Matcher.find() works as expected (returning true).


---------- BEGIN SOURCE ----------
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class MatcherTest {
    public static void main(String[] args) {
        checkHitEnd("normal", MatcherTest::checkHitEndNormal);
        checkHitEnd("incomplete surrogate pair", MatcherTest::checkHitEndIncompleteSurrogatePair);
    }
    
    private static void checkHitEnd(String checkName, Predicate<Consumer<Matcher>> checkMethod) {
        System.out.println("hitEnd(): " + checkName);
        System.out.println(" matches: " + checkMethod.test(Matcher::matches));
        System.out.println(" lookingAt: " + checkMethod.test(Matcher::lookingAt));
        System.out.println(" find: " + checkMethod.test(Matcher::find));
    }

    private static boolean checkHitEndNormal(Consumer<Matcher> matcherAction) {
        final String input = "abc";
        final Pattern pattern = Pattern.compile("abcd");
        final Matcher matcher = pattern.matcher(input);
        matcherAction.accept(matcher);
        return matcher.hitEnd();
    }
    
    private static boolean checkHitEndIncompleteSurrogatePair(Consumer<Matcher> matcherAction) {
        final String hexString = "1F30C";
        final char[] chars = Character.toChars(Integer.parseInt(hexString, 16));
        final Pattern pattern = Pattern.compile("\\x{" + hexString + "}");
        final Matcher matcher = pattern.matcher(String.valueOf(chars[0]));
        matcherAction.accept(matcher);
        return matcher.hitEnd();
    }
}

---------- END SOURCE ----------

FREQUENCY : always