It certainly is, Stubborn. St. Alphonsus said it was de fide. Numerous Popes said Catholics may safely repeat any doctrine St. Alphonsus taught in the Moral Theology work where he said this.
Yes, I know he is safe to quote anything in his Moral Theology. That the sacrament is necessary for salvation is a dogma, it was defined at Trent and therefore belongs with Dogmatic Theology, not Moral Theology. Yet he got it absolutely correct in my previous post to you.
Again, Trent's "no justification without the desire" does not mean "justification with the desire". It simply doesn't. The way Trent infallibly puts it, one may or may not be justified via desire, they left it that way on purpose.
1) If you were asked, "can one be justified if they have a desire for the sacrament"? You must answer - "all I know for sure is that without the desire, they cannot be justified".
2) If one were to ask you "is anyone saved without the sacrament"? You must answer - "the sacraments are necessary for salvation".
You can never be wrong by repeating Trent, which is what 1 and 2 both do.
Aside from the canon saying it explicitly in the first part, the negative tenor of the second part of the canon teaches that the only sure way of obtaining justification is to receive the sacrament, which is also necessary for salvation. Without the sacrament, no one can attain salvation or justification. Without the desire for the sacrament, no one can be justified. Whatever anyone else teaches that differs from this, this is the teaching of Trent.
If you're understanding of Trent does not agree with this, then you are not understanding Trent's teaching.