parser.Trace not working

[edgar hoover]

Hi all,
I've hit some odd behaviour that may be a bug somewhere in antlr (or may be me).

To try to track it down I tried using the trace thingy

...
var tokens = new CommonTokenStream(lexer);
var parser = new LDBParser(tokens);
parser.Trace = true;    <------------- added this
var listener = new ErrorListener<IToken>(parser, lexer, tokens);
...

But when run this gives

System.NullReferenceException
  HResult=0x80004003
  Message=Object reference not set to an instance of an object.
  Source=Antlr4.Runtime.Standard
  StackTrace:
   at Antlr4.Runtime.Parser.TraceListener.EnterEveryRule(ParserRuleContext ctx)
   at Antlr4.Runtime.Parser.TriggerEnterRuleEvent()
   at Antlr4.Runtime.Parser.EnterRule(ParserRuleContext localctx, Int32 state, Int32 ruleIndex)
   at LDB.LDBParser.start_parse() in [full path snipped]\LDB\obj\Debug\netcoreapp3.1\LDBParser.cs:line 1370

Is this an antlr problem or do I need to set some extra configs or something?

thanks

jan

[Martin Mirchev]

Yep, already filled an issue in Github. You are gonna have to use reflection to fix the tracer.

[edgar hoover]

Hi, per my other question which turns out to be me not antlr (well surprise),
I've no idea on what you mean by using reflection to fix it, can you post a few links please?

thanks

jan

[Martin Mirchev]

When you set .trace to true , the tracing listener it has does not have a stream set, so it throws a null pointer exception. If you put your own Trace Listener, which you construct from the consturctor, it does not have a reference to a parser. Link to faulty code. You will have to set the private field _enclosing (when you create a TraceListener) or Output,(if you use the original tracer).

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