Add ability to get all possible next tokens for autocompletion use

Bruno LETRESTE points out:

i use yours getExpectedToken after i move to position in my algorithm my algorithm check the tokens and try to find the real path (in ATN tree) it stock the potential terminate for solve for exemple (and add potential to expected token)

expr : '(' expr ')'
       | expr '+' expr
       | ID
       ;

for exemple in this case, if i have ( ID I get expected token return + but it should have ) as well.

[mike-lischke]

Ah, good you reminded me. The C++ implementation is on Github since a few weeks already. However, there’s no readme or other document in that repo for this code. However, I have a port (or rather a parallel development) of this idea written in Typescript (and there are ports of that code to Kotlin and Java). And this repo also contains some documentation how to configure and use the engine. Let’s discuss there if you have any questions.

[kaby76]

I’ve noticed with Mike Lischke’s implementation that it does not compute the lookahead sets correctly in some situations. In particular, for Antlr grammars, if I want the lookahead set after a parser rule semicolon, I get an incomplete set that also includes epsilon but should not. Starting with Mike’s implementation, and Parr’s LL(*) paper, I derived a similar algorithm (http://codinggorilla.com/?p=2449) and have C# implementations for code completion in an LSP server and for error reporting in a Net Core Antlr “Hello World” template (https://github.com/kaby76/Antlr4BuildTasks/blob/master/Templates/templates/AntlrCAProject/LASets.cs). Note, the design is recursive and makes a call per an edge/token match, so I don’t doubt stack overflow issues in construction of a parse. One step at a time.