flatAndMerge中的泛型类型Item为什么不能推导出来？未知。

type ItemRecord<Item> = Record<string, Item>

export const objectToFlatList = <Item>(data: ItemRecord<Item>) =>
  Object.keys(data).map((key) => ({ key, ...data[key] }));

export const flatAndMerge = <
  Item,
  T extends Record<string, ItemRecord<Item>>,
>(
  data: T,
  fields: (keyof T)[],
) => fields.flatMap((field) => objectToFlatList(data[field]));

const a = flatAndMerge(
  {
    a: {
      aa: { foo: 'foo' } ,
      ab: { foo: 'foo' },
    },
    b: {
      ba: { foo: 'foo' },
      bb: { foo: 'foo' },
    },
    c: {
      ca: { foo: 'foo' },
      cb: { foo: 'foo' },
    },
  } as Record<string, ItemRecord<{ foo: string }>>, //
  ['a', 'c'],
);

作为备注：objectToFlatList推断类型正确。