Adding a literal token to a grammar file when it had already been defined in the lexer file - is this legal?

[The-Futurist]

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If I have a grammar g4 file and a lexer g4 file.

Then inadvertently insert a literal token like { into the grammar (when that same token has actually been defined in the lexer already) then is that legal or not?

I did this by mistake and it causes all sorts of weiredness in the antlr VS Code extension (which I just reported) but antlr itself doesn't complain, it process these files with that kind of change and generates .tokens files and does not report any error.

So in my lexer I had this (which I'd forgotten about):

Which I'd totally forgotten about. But in my grammar g4 I simply changed this:

to this

then saved the change and then reran antlr and it ran fine but the antlr GUI tool does not, it gets very upset!