Accessing the current lexer mode in a custom error message

[nk-coding]

Hi,
I want to provide a custom error message for an unexpected character using buildUnexpectedCharactersMessage.
The error message should depend on the current mode of the lexer. Is this possible, and if yes, how?

[msujew]

Hey @nk-coding,

as far as I'm aware, the lexer does not expose the current mode to the ILexerErrorMessageProvider in any way. Since the lexer mode also isn't a property of the lexer itself, but a local variable of the tokenize method, I don't think there's a way to retrieve the value.

[bd82]

I actually think this should be fairly easy.

1. The buildUnexpectedCharactersMessage api is called from tokenize method - link
2. The Tokenize method has an internal state (stack) tracking the modes link
3. This state variable is at the top most context/scope of the tokenize method, so should be accessible anywhere "deeper" in the method.

You can try editing the tokenize method source code directly in node_modules to produce this effect.
If it works you can provide a PR.

[msujew]

Right, I wasn't saying that it's difficult to add as an improvement in Chevrotain. But at least right now, the library does not expose the necessary data for adopters.

[nk-coding]

hi, thanks for looking into this.
I just tried it out and it seems to work fine so far.
I will try to provide a PR the next days/weeks