How to control error handling and synchronization in Antlr 4 / c#

Question

I\'m using Antlr 4 with c# target. Here is a subset of my grammar:

/*
 * Parser Rules
 */
text : term+  EOF;
term : a1 a2 a3;
a1: ....
...
...

Answer 1

For the first question (How to synchronize input to the next valid term?) I found some useful information that led me to acceptable solution.

Antlr generates next subcode for previous grammar:

public TextContext text() {
    TextContext _localctx = new TextContext(_ctx, State);
    EnterRule(_localctx, 0, RULE_text);
    int _la;
    try {
        EnterOuterAlt(_localctx, 1);
        State = 49;
        _errHandler.Sync(this);
        _la = _input.La(1);
        do {
            State = 48; term();
            State = 51;
            _errHandler.Sync(this);
            _la = _input.La(1);
        } while ( _la==KEYWORD );
        State = 53; Match(EOF);
    }
    catch (RecognitionException re) {
        _localctx.exception = re;
        _errHandler.ReportError(this, re);
        _errHandler.Recover(this, re);
    }
    finally {
        ExitRule();
    }
    return _localctx;
}

The call '_errHandler.Sync(this);' makes the parser advances through the input stream in an attempt to find next valid turn (as a result of "term+" component). To stop parser from sync in other subrules accept "term" rule", I Extended DefaultErrorStrategy Class as next:

public class MyErrorStrategy : Antlr4.Runtime.DefaultErrorStrategy
{
    public EventErrorStrategy() : base()
    { }

    public override void Sync(Antlr4.Runtime.Parser recognizer)
    {
        if(recognizer.Context is Dict.TextAnalyzer.DictionaryParser.TextContext)
            base.Sync(recognizer);
    }
}

then provided it to the parser:

parser.ErrorHandler = new MyErrorStrategy();