Fix operator overloading pre-selection: reverse subtyping only if abs…

…tract type

dev/src/lobster/typecheck.h

@@ -615,7 +615,8 @@ struct TypeChecker {
  return nullptr;
  };
  auto child1 = n.Children()[0];
- if (!IsUDT(child1->exptype->t)) return no_overload();
+ auto ctype = child1->exptype;
+ if (!IsUDT(ctype->t)) return no_overload();
  auto opname = TName(T_OPERATOR) + (n.Name() == "indexing operation" ? "[]" : n.Name());
  auto it = st.operators.find(opname);
  if (it == st.operators.end()) return no_overload();
@@ -624,22 +625,22 @@ struct TypeChecker {
  f = f->sibf;
  if (!f) return no_overload();
  }
- // Here all we care about is to see that child1->exptype has some kind of operator
+ // Here all we care about is to see that ctype has some kind of operator
  // overload specified for it, so that TypeCheckCall can do the actual work of finding
  // the correct overload (and we don't have to duplicate that here).
  for (auto [i, ov] : enumerate(f->overloads)) {
  auto atype = ov->sf->args[0].type;
  if ((atype->t == V_UUDT &&
- (DistanceToSpecializedSuper(atype->spec_udt->gudt, child1->exptype->udt) >= 0 ||
- DistanceFromSpecializedSub(child1->exptype->udt, atype->spec_udt->gudt) >= 0)) ||
- ConvertsTo(child1->exptype, atype, CF_NONE) ||
- ConvertsTo(atype, child1->exptype, CF_NONE) /* child is abstract type? */) {
+ (DistanceToSpecializedSuper(atype->spec_udt->gudt, ctype->udt) >= 0 ||
+ (ctype->udt->g.is_abstract && DistanceFromSpecializedSub(ctype->udt, atype->spec_udt->gudt) >= 0))) ||
+ ConvertsTo(ctype, atype, CF_NONE) ||
+ (ctype->udt->g.is_abstract && ConvertsTo(atype, ctype, CF_NONE))) {
  goto have_candidates;
  }
  }
  return no_overload();
  have_candidates:
- if (n.SideEffect() && IsStruct(child1->exptype->t))
+ if (n.SideEffect() && IsStruct(ctype->t))
  Error(n, "struct types can\'t model side effecting overloaded operators");
  if (n.Arity() > 1) TT(n.Children()[1], 1, LT_ANY);
  auto c = new Call(n.line, f->overloads[0]->sf);