src/vs/platform/undoRedo/common/undoRedoService.ts/UndoRedoService/undo
class UndoRedoService:	public undo(resourceOrSource: URI | UndoRedoSource): Promise<void> | void {
		if (resourceOrSource instanceof UndoRedoSource) {
			const [, matchedStrResource] = this._findClosestUndoElementWithSource(resourceOrSource.id);
			return matchedStrResource ? this._undo(matchedStrResource, resourceOrSource.id, false) : undefined;
		}
		if (typeof resourceOrSource === 'string') {
			return this._undo(resourceOrSource, 0, false);
		}
		return this._undo(this.getUriComparisonKey(resourceOrSource), 0, false);
	}