Preheat the oven to 350°F. Grease a smaller baking pan (8x8 inch or similar) with butter or non-stick spray.
Peel and core the Granny Smith apples. Cut into 6–8 wedges per apple.
Separate the crescent roll dough into triangles. Wrap each apple wedge, starting at the wide end and rolling toward the point.
Place the wrapped apples in the prepared pan.
Melt the butter in a saucepan over medium heat. Stir in the sugar and vanilla until combined. Add cinnamon to taste.
Pour the butter-sugar mixture over the dumplings.
Gently pour the citrus soda around the edges of the pan and into the gaps between the dumplings. Avoid pouring directly over the dumplings, to keep the tops crisp.
Bake 35–40 minutes, until golden brown and the sauce is bubbly.
Allow to cool slightly. Serve warm, optionally with ice cream or whipped cream.