minecraft-assets/data/minecraft/recipe/hopper_minecart.json

{
  "type": "minecraft:crafting_shapeless",
  "category": "misc",
  "ingredients": [
    "minecraft:hopper",
    "minecraft:minecart"
  ],
  "result": {
    "count": 1,
    "id": "minecraft:hopper_minecart"
  }
}