Failed to solve the following constraints:
  Check definition of foo : (y : D _x_12) → P _x_12 y
    stuck because
      Issue1863.agda:17,5-6
      I'm not sure if there should be a case for the constructor d,
      because I get stuck when trying to solve the following unification
      problems (inferred index ≟ expected index):
        i tt ≟ _x_12
      when checking that the pattern d has type D _x_12
    (blocked on _x_12)
Unsolved metas at the following locations:
  Issue1863.agda:16,19-20
