src/vs/platform/undoRedo/common/undoRedoService.ts/UndoRedoService/_findClosestRedoElementWithSource
class UndoRedoService:	private _findClosestRedoElementWithSource(sourceId: number): [StackElement | null, string | null] {
		if (!sourceId) {
			return [null, null];
		}

		// find an element with sourceId and with the lowest sourceOrder ready to be redone
		let matchedElement: StackElement | null = null;
		let matchedStrResource: string | null = null;

		for (const [strResource, editStack] of this._editStacks) {
			const candidate = editStack.getClosestFutureElement();
			if (!candidate) {
				continue;
			}
			if (candidate.sourceId === sourceId) {
				if (!matchedElement || candidate.sourceOrder < matchedElement.sourceOrder) {
					matchedElement = candidate;
					matchedStrResource = strResource;
				}
			}
		}

		return [matchedElement, matchedStrResource];
	}