T12530.hs:(8,3)-(15,6): Splicing declarations
    [d| f :: Maybe Int -> Maybe Int
        f = id @(Maybe Int)
        g :: forall a. a
        g = undefined @(_) @(a) |]
  ======>
    f :: Maybe Int -> Maybe Int
    f = id @(Maybe Int)
    g :: forall a. a
    g = undefined @_ @a