Go runtime panic

[parrt]

@chenquan reported bug here: #3834 (comment)

I found this problem in github.com/antlr/antlr4/runtime/Go/antlr v1.4.10. grammar:https://github.com/antlr/grammars-v4/tree/master/sql/mysql/Positive-Technologies

panic: interface conversion: antlr.PredictionContext is *antlr.EmptyPredictionContext, not *antlr.ArrayPredictionContext [recovered]
	panic: interface conversion: antlr.PredictionContext is *antlr.EmptyPredictionContext, not *antlr.ArrayPredictionContext [recovered]
	panic: interface conversion: antlr.PredictionContext is *antlr.EmptyPredictionContext, not *antlr.ArrayPredictionContext

[jimidle]

@parrt @chenquan I cannot reproduce this with the latest runtime code. I have some recollection of fixing this as part of some other code fix, but I cannot be sure. Code should refer to the PredictionContext interface rather than a specific instance. I believe that I fixed this as a byproduct of changing the code that calls mergeArrays, many months ago.

I ran the code above and with the generated visitor it all works as I would expect and there is no panic.

BTW - would you please report bugs with code, rather than a screenshot, so I can be sure I am running the same thing? Cheers :).

I think that this can be closed.