Type alias circularly references itself error

[mjbvz]

Steps to reproduce

type IndentationTree<L> = TopNode<L> | VirtualNode<L> | LineNode<L> | BlankNode<L>;
type IndentationSubTree<L> = Exclude<IndentationTree<L>, TopNode<L>>;

interface NodeBase<L> {
	subs: IndentationSubTree<L>[];
}

interface VirtualNode<L> extends NodeBase<L> {
	type: 'virtual';
}

interface TopNode<L> extends NodeBase<L> {
	type: 'top';
}

interface LineNode<L> extends NodeBase<L> {
	type: 'line';
}

interface BlankNode<L> extends NodeBase<L> {
	type: 'blank';
}

Behavior with typescript@5.8

No errors in 5.8.3

Behavior with tsgo

This is an error in tsgo

[ahejlsberg]

This is a property ordering issue (similar to type ordering). In Strada we order explicitly declared properties before inherited properties in the internal representation, whereas in Strada we order properties by their source location. In the repro this means that we relate type properties first in Strada, but subs properties first in Corsa.

You can force the error to occur in Strada by not inheriting from NodeBase and explicitly declaring subs properties before the type properties in each of the node types. Conversely, you can make the error go away in Corsa by moving the NodeBase declaration past the specific node types.

There's something to be said for relating explicitly declared properties before inherited properties because the explicitly declared properties are more likely to contain discriminating differences, so I'll think about ways to incorporate that in Corsa.