Declared Types cannot include Keywords as Properties

Present in Langium version: 0.4.0

We can currently generate AST types via inference that include various Langium keywords as properties, like so:

A: interface=ID type=ID grammar=ID;

infers…

export interface A extends AstNode {
    grammar: string
    interface: string
    type: string
}

However, if cannot do the same via declared types. The following is an example demonstrating how this fails, but also shows that Langium is highlighting the properties incorrectly as keywords.

Unless we intend to remove these properties from being used via inference, we should also support them in their declared forms.

To solve this:

• we should be able to declare the same properties via inference as we can explicitly
• we should have a test verifying this behavior
• if we choose to block certain keywords, we’ll need extra tests guarding against those keywords (should we choose this route instead)

[msujew]

@montymxb There’s a special data type rule that can be used to work around the ^ token:

https://github.com/langium/langium/blob/207b6e59f063d04825ab77185cda1baa96b7ee25/packages/langium/src/grammar/langium-grammar.langium#L198-L199

[msujew]

You can always escape keywords using the ^ token at the start of the ID. But anway, we should use the appropriate data type rule for the names of properties.