langium custom Validator

[zrwsmd]

i validate st program name should start with /^\d/.test(program.name) for eaxmple,.
if i use true instead of isStartsWithNumber variable,it hint below message,but replace isStartsWithNumber variable with true did hint
this message

[msujew]

I'm sorry, what? I don't really understand what the question/issue is. Can you elaborate a bit?

[msujew]

Can you show the terminal that you use to parse the name property of the Program type? There might be a parser error that prevents the assignment of the name property.

[zrwsmd]

Namespace:
'NAMESPACE' name=ID
(elements+=AbstractElement)*
'END_NAMESPACE'
;

terminal ID: /[a-zA-Z][\w_&]*/;

[msujew]

Your name property is never assigned, since the ID cannot start with a digit. Only a-z and A-Z are valid characters. That's why the error doesn't appear when you try to test for the first digit. program.name is simply undefined due to the parser error.

[zrwsmd]

so langium parse error and custom validation error can not appear at the same time?or how to fix it

[msujew]

Not if they are in the exact same token, no. If the parser expects an ID, and receives a number, it won't attempt to assign the number to the field that is supposed to be an ID.

The presence of parser errors will lead to non-valid ASTs.

You fix it by allowing your IDs to start with numbers. Note that this will lead to a lexer conflict if you have a number terminal rule.