(fix) lib: unmatched groups

lib/src/main/java/org/pcre4j/Pcre4jUtils.java

@@ -256,7 +256,15 @@ public static int[] convertOvectorToStringIndices(String subject, byte[] subject
         // Convert byte offsets to string indices
         final var stringIndices = new int[ovector.length];
         for (var valueIndex = 0; valueIndex < ovector.length; valueIndex++) {
-            stringIndices[valueIndex] = byteOffsetToStringIndex[(int) (ovector[valueIndex] - ovector[0])];
+            final var byteIndex = ovector[valueIndex];
+
+            // Handle case when group was not matched
+            if (byteIndex == -1) {
+                stringIndices[valueIndex] = -1;
+                continue;
+            }
+
+            stringIndices[valueIndex] = byteOffsetToStringIndex[(int) (byteIndex - ovector[0])];
         }
 
         return stringIndices;

regex/src/test/java/org/pcre4j/regex/MatcherTests.java

@@ -618,4 +618,32 @@ void captureGroups() {
         assertEquals(javaMatcher.end("two"), pcre4jMatcher.end("two"));
     }
 
+    @Test
+    void unmatchedGroups() {
+        var regex = "42((?<exclamation>!)|(?<question>\\?))";
+        var input = "42!";
+        var javaMatcher = java.util.regex.Pattern.compile(regex).matcher(input);
+        var pcre4jMatcher = Pattern.compile(regex).matcher(input);
+
+        assertEquals(javaMatcher.find(), pcre4jMatcher.find());
+
+        assertEquals(javaMatcher.group(), pcre4jMatcher.group());
+        assertEquals(javaMatcher.group(0), pcre4jMatcher.group(0));
+        assertEquals(javaMatcher.group(1), pcre4jMatcher.group(1));
+        assertEquals(javaMatcher.group(2), pcre4jMatcher.group(2));
+        assertEquals(javaMatcher.groupCount(), pcre4jMatcher.groupCount());
+        assertEquals(javaMatcher.start(), pcre4jMatcher.start());
+        assertEquals(javaMatcher.start(0), pcre4jMatcher.start(0));
+        assertEquals(javaMatcher.start(1), pcre4jMatcher.start(1));
+        assertEquals(javaMatcher.start(2), pcre4jMatcher.start(2));
+        assertEquals(javaMatcher.start("exclamation"), pcre4jMatcher.start("exclamation"));
+        assertEquals(javaMatcher.start("question"), pcre4jMatcher.start("question"));
+        assertEquals(javaMatcher.end(), pcre4jMatcher.end());
+        assertEquals(javaMatcher.end(0), pcre4jMatcher.end(0));
+        assertEquals(javaMatcher.end(1), pcre4jMatcher.end(1));
+        assertEquals(javaMatcher.end(2), pcre4jMatcher.end(2));
+        assertEquals(javaMatcher.end("exclamation"), pcre4jMatcher.end("exclamation"));
+        assertEquals(javaMatcher.end("question"), pcre4jMatcher.end("question"));
+    }
+
 }