fix regex error messages WIP

Author: fglock

src/main/java/org/perlonjava/regex/RegexPreprocessorHelper.java

@@ -233,19 +233,25 @@ static int handleEscapeSequences(String s, StringBuilder sb, int c, int offset)
                 sb.append("[^\\n]");
                 return offset;
             }
-        } else if ((nextChar == 'p' || nextChar == 'P') && offset + 1 < length && s.charAt(offset + 1) == '{') {
-            // Handle \p{...} and \P{...} constructs
-            boolean negated = (nextChar == 'P');
-            offset += 2; // Skip past \p or \P
-            int endBrace = s.indexOf('}', offset);
-            if (endBrace != -1) {
-                String property = s.substring(offset, endBrace).trim();
-                String translatedProperty = translateUnicodeProperty(property, negated);
-                sb.setLength(sb.length() - 1); // Remove the backslash
-                sb.append(translatedProperty);
-                offset = endBrace;
+        } else if ((nextChar == 'p' || nextChar == 'P')) {
+            if (offset + 1 < length && s.charAt(offset + 1) == '{') {
+                // Existing code for \p{...} and \P{...}
+                boolean negated = (nextChar == 'P');
+                offset += 2; // Skip past \p{ or \P{
+                int endBrace = s.indexOf('}', offset);
+                if (endBrace != -1) {
+                    String property = s.substring(offset, endBrace).trim();
+                    String translatedProperty = translateUnicodeProperty(property, negated);
+                    sb.setLength(sb.length() - 1); // Remove the backslash
+                    sb.append(translatedProperty);
+                    offset = endBrace;
+                } else {
+                    RegexPreprocessor.regexError(s, offset, "Missing right brace on \\\\p{}");
+                }
             } else {
-                RegexPreprocessor.regexError(s, offset, "Missing right brace on \\\\p{}");
+                // \p or \P without brace
+                RegexPreprocessor.regexError(s, offset + 1,
+                    "Character following \\" + nextChar + " must be '{' or a single-character Unicode property name");
             }
         } else {
             int c2 = s.codePointAt(offset);