grammar - 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: ....
...
...

I want to accept valid data blocks as (term)s, when error exists I want to search for the next valid term and print out the whole text which caused the error for user to analyze manually.

How to synchronize input to the next valid term? and How to get the ignored text?

Answer 1

You will need to create your own implementation of IAntlrErrorStrategy for this, and then set the Parser.ErrorHandler property to an instance of your error strategy. The documentation for the Java versions of the ANTLRErrorStrategy interface and default implementation DefaultErrorStrategy may provide useful information for implementing an error strategy, but I must warn you going in that creating a custom error strategy is an advanced feature with limited documentation. It's expected that the implementer is already an expert in ANTLR 4's implementation of the Adaptive LL(*) parsing algorithm (we're talking researcher-level understanding).