disambiguate enum blocks and complete distinct type operations

compiler/types/types.odin

@@ -1106,9 +1106,33 @@ is_runtime_value :: proc(value: Type, store: ^Store, depth := 0) -> bool {
 	return false
 }
 
-can_construct_distinct :: proc(from, to: Type, store: ^Store) -> bool {
-	item, ok := node(store, to)
-	return ok && item.kind == .Distinct && item.declared && equal(from, item.child)
+distinct_backing :: proc(value: Type, store: ^Store) -> (Type, bool) {
+	item, ok := node(store, value)
+	if !ok || item.kind != .Distinct || !item.declared {
+		return INVALID, false
+	}
+	return item.child, true
+}
+
+distinct_scalar_backing :: proc(value: Type, store: ^Store) -> (Type, bool) {
+	_, ok := distinct_backing(value, store)
+	if !ok {
+		return INVALID, false
+	}
+	backing := runtime_representation(value, store)
+	return backing, is_concrete_scalar(backing)
+}
+
+can_retype_distinct :: proc(from, to: Type, store: ^Store) -> bool {
+	if backing, ok := distinct_backing(to, store); ok && equal(from, backing) {
+		return true
+	}
+	backing, ok := distinct_backing(from, store)
+	if !ok || !equal(to, backing) {
+		return false
+	}
+	_, scalar := distinct_scalar_backing(from, store)
+	return scalar
 }
 
 runtime_representation :: proc(value: Type, store: ^Store, depth := 0) -> Type {