introduced dedicated interface PrecomputedScopes, updated implementations of DefaultScopeComputation and DefaultScopeProvider

[sailingKieler]

With this additional method hook, customized implementations of PrecomputedScopes contributing lazily computed proposals (for the sake of memory usage optimization) can be employed, and eager in-between evaluations can be avoided by overriding the new method hook getStream(key).

[msujew]

Are you overriding MultiMap in your adopter code? This change feels like the wrong abstraction layer. I would much rather have a dedicated PrecomputedScope interface (with a default implementation based on MultiMap), than extend the data type based on a specific adopter need. You can then create your own, stream based PrecomputedScope implementation.

[sailingKieler]

I introduced an

CustomPrecomputedScopes extends MultiMap<AstNode, AstNodeDescription> {

    private lazyComputations = new Map<AstNode, () => Stream<AstNodeDescription>>();
    
    ...

    public getStream(key: AstNode): Stream<AstNodeDescription> {
        const local = stream(super.get(key)); // to be replaced with `super.getStream(key)`
        const additional = this.lazyComputations.get(key);
        return local && additional ? local.concat(additional()) : local ?? additional?.() ?? stream();
    }
}

Indeed, from an outside point-of-view the additional method looks a bit weird, with the constraint in mind that the memory footprint of the precomputed scopes might get too high with a high number of documents this is the origin of the change (instead of the array-based inclusion)

langium/packages/langium/src/references/scope-provider.ts

Lines 59 to 63 in 8078681

	const allDescriptions = precomputed.getStream(currentNode);
	if (!allDescriptions.isEmpty()) {
	scopes.push(stream(allDescriptions).filter(
	desc => this.reflection.isSubtype(desc.type, referenceType)));
	}

Motivation: Constraint-based visibility of external symbols per document.

[sailingKieler]

@msujew I pushed a new version. Does that one meet your idea/proposal?