Best way to restrict references? #360

paulfrench · 2022-01-13T17:32:28Z

paulfrench
Jan 13, 2022

Here is a grammar file I've simplified to demonstrate my problem...

grammar Cleese
hidden(WS, SL_COMMENT, ML_COMMENT)

Model:
	(elements+=Element)*;

Element:
	Entity;

Entity:
	'entity' name=ID ('extends' superType = [Entity])? '{'
		(properties+=Property)*
    ('keys' ':' '[' keys+=[Property]("," keys+=[Property])* ']' )?
	'}';

Property:
	name=ID ':' type=AllTypes;

AllTypes:
  Type | 'List' '<' Type '>';

Type:
	EntityReference | SimpleDataType;

EntityReference:
	type=[Entity];

SimpleDataType:
	type=PrimitiveType;

PrimitiveType returns string:
	"number" | "string" | "date" | "boolean";


terminal WS: /\s+/;
terminal ML_COMMENT: /\/\*[\s\S]*?\*\//;
terminal SL_COMMENT: /\/\/[^\n\r]*/;

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

I can create a Entity no problem and auo-completion works great for the supertype and for the keys.

entity Address {
  id: number
  line1: string
  postcode: string
  keys : [ id ]
}

entity Person {
  id: number
  firstname: string
  surname: string
  address: Address
  keys : [ id ]
}

The question is how to I modify the grammar so that the auto-suggestions for the keys that can be used in the Person entity is only the properties that are primitive types? At the moment, "id", "firstname", "surname" and "address" get auto suggested, but a key cannot be a complex object and so I do not want the "address" to be auto-suggested as a key?

I'm missing something somewhere in my understanding of how to construct the grammar and possibly not try and do everything in the grammar itself and instead write validation rules? Not sure, any guidance would be great!

Answered by spoenemann

Jan 14, 2022

There are multiple ways to solve that:

Split the Property rule in two variants, one for primitive types and one for complex types, and use the primitive variant in the cross-reference (not recommended).
Change the ScopeProvider service so it filters the properties to include only those with primitive types (not recommended).
Add a validation check that shows an error when a property with complex type is used as key, and adapt the CompletionProvider service to show only the properties with primitive type for that cross-reference.

I recommend the third approach because it results in a much better error message to the users: Instead of "Could not resolve reference..." they will see somethi…

View full answer

spoenemann · 2022-01-14T07:37:48Z

spoenemann
Jan 14, 2022
Maintainer

There are multiple ways to solve that:

Split the Property rule in two variants, one for primitive types and one for complex types, and use the primitive variant in the cross-reference (not recommended).
Change the ScopeProvider service so it filters the properties to include only those with primitive types (not recommended).
Add a validation check that shows an error when a property with complex type is used as key, and adapt the CompletionProvider service to show only the properties with primitive type for that cross-reference.

I recommend the third approach because it results in a much better error message to the users: Instead of "Could not resolve reference..." they will see something like "Only primitive types can be used as keys".