How to create more precise error messages?

[LNow]

When we use following code as input in json grammar example then error message we get says:
Expecting --> '}' <-- but found --> '"lastName"' <--

{
	"firstName": "John"
	"lastName": "Smith",
	"isAlive": true,
	"age": 25
}

What changes needs to be applied to grammar to get Expecting --> ',' <-- but found --> '"lastName"' <-- or Expecting --> ',' <-- or --> '}' <-- but found --> '"lastName"' <-- instead?

[bd82]

Hi @LNow

I can't immediately think of such a change, basically the repetition of the key/value pairs is terminated due to the lack of comma
and the error happens "after" the repetition when closing the JSON object is expected.

You may be able to customize the error message text if you can recognize the scenario given
the context in the custom error messages APIs.

• https://chevrotain.io/docs/features/custom_errors.html

Adding logic to identify the situation inside the grammar and throw a user defined syntax error
could also work, but will probably depend on:

• Custom User Defined Syntax Errors #646 (which should be a small fix).