allow parser syntax errors to stop parser tree walking

OscCommentMacroListener.py

@@ -177,11 +177,7 @@ class OscCommentMacroListener(CommentMacroListener):
         if ctx.target()is None:
             logger.error("ERROR: limited to fading specified masters only.")
             return
-        try:
-            level = ctx.number().value
-        except AttributeError:
-            logger.error("ERROR: level arument is required!")
-            return
+        level = ctx.number().value
         if (level < 0 or level > 100):
             logger.error("Level must be between 0 and 100.")
             return

comment.py

@@ -20,12 +20,19 @@ import configparser
 import logging
 import sys
 
+from antlr4.error.ErrorListener import ErrorListener
 from CommentMacroLexer import CommentMacroLexer
 from CommentMacroParser import CommentMacroParser
 from OscCommentMacroListener import OscCommentMacroListener
 from pythonosc import udp_client
 
 
+# define an error listener that raises SyntaxError exceptions
+class SyntaxErrorListener(ErrorListener):
+    def syntaxError(self, recognizer, offendingSymbol, line, column, msg, e):
+        raise SyntaxError('line ' + str(line) + ': ' + msg)
+
+
 # setup logging
 logger = logging.getLogger(__name__)
 logger.setLevel(logging.DEBUG)
@@ -50,7 +57,12 @@ def comment(text):
     lexer = CommentMacroLexer(input_stream)
     stream = antlr4.CommonTokenStream(lexer)
     parser = CommentMacroParser(stream)
-    tree = parser.prog()
+    parser._listeners = [SyntaxErrorListener()]
+    try:
+        tree = parser.prog()
+    except SyntaxError as e:
+        logger.error(e)
+        return
     oscMacro = OscCommentMacroListener(servers)
     walker = antlr4.ParseTreeWalker()
     walker.walk(oscMacro, tree)