AntlrVSIX is a language server for use with Visual Studio 2019, Visual Studio Code, and Gnu Emacs to support Antlr, Bison, and W3C EBNF grammars. In addition to the IDE extensions provided here, a command-line tool is available to refactor grammars in order to make them cleaner, more readable, and more efficient.
Lexer errors are not being caught for Antlr3 parsing, and elsewhere. Consequently, it reports back all okay to the client.