I have seen a discussion regarding Harry Potter quotes, such as:
Voldemort will not have made it easy to discover his hiding place.
Which is said in a situation when Voldemort had hidden the thing already (in the past). But I am thinking – if I did not know the context, I could think that he has yet to hide it (and will not make it easy, is that correct?)
Why is this tense used here, as a prediction?
What if I say:
Voldemort surely did not make it easy to discover his hiding place.
Is this the same as using would have for past speculations? Such as in:
In those ages, people would have used bones to craft weapons.
Which I believe is the same like “were likely using”
will have made = probably did make
The short answer is that in your example, will not have made carries the sense of probably didn’t make. It’s talking about a past event, not a future one.
You probably shouldn’t be thinking in terms of tenses (read: inflectional morphology) at all as soon as modal verbs are involved. This is a modal, which means there’s no tense involved here, except insofar as the present-tense will becomes the past-tense would under backshifting.
This is simply an epistemic modal indicating probability. It means he probably did not make it easy.
You second example uses would, which can also be used to indicate habitual past action as well as for probability.
video, videro: Why English has no “future perfect tense”
There isn’t any such word-form as a “future perfect tense” in English. Latin has a future perfect tense, but English does not.
Tense refers to the form of just one word, like see versus saw. Once you start stringing together more words like in will have been being seen, you aren’t talking about a tense at all. Each of those inflected words is in one or another inflection of some verb, but the whole verb phrase cannot be said to be in any “tense”.
To see the difference, we can look at Latin, a language which actually does have an actual future perfect tense. So for example the word video means “I see” in Latin. Both video and see are in the present tense. (Or at least see is not in the past tense. In some analyses, English can be said to have only past and non-past for its two tenses, not past and present.)
So video does have a future perfect tense: it’s videro, just as the past perfect tense of video is videram. Those respectively mean “I will have seen” and “I had seen” in English, but there is no single word in the English version which is in any such tense as “future perfect”: will is a present-tense inflection of an otherwise defective modal verb which we regularly put to many sorts of epistemic and deontic uses, have is the bare infinitive of that verb, and seen is the part-participle inflection of see. You’re welcome to call will have seen a future-perfect construction if you wish, but it’s not a tense. Too many words.
Just because the meaning is the same doesn’t mean that the inflectional morphology is. That’s why you can express the same thing in English as the Romans did when they used a future perfect tense, but that doesn’t make what you’re doing in English a future perfect tense — because English has no such morphological inflection of its verbs.
When people talk about the “future perfect” in English, they are not talking about the form of a word, but rather to a time-related sense for the verb phrase itself, a sense which is unrelated to inflectional morphology of each individual word and which is constructed on the fly by stringing together several verbs each in different inflections.
English-as-a-foreign-language instructional materials tend to short-cut matters and call things like the “present continuous” or “past habitual” or “future perfect” tenses, but that is not what linguists mean by the word “tense”.
See also “synthetic tenses versus analytic tenses”.