I have noticed there is a way of using 'must have' to denote finished obligation in the future - somewhat akin to the 'future perfect tense'. An example of what I mean:
" I must have finished this exercise by tomorrow"
To me, "I must finish this exercise by tomorrow" would be just sufficient, but the above example is especially confusing because it seems to make perfect sense, and yet it seems to violate a rule of thumb I picked up, which is that 'must have' can only be used to express a deduction or an assumption concerning the past.
eg: "He must have dropped the pen by mistake " meaning 'I believe most certainly he did'.
All the references I checked do not cover this particular use of 'must + past-perfect'. If there were no time signifier - 'by tomorrow' in this example - I would squarely think that this is a statement about the past. So, at the risk of sounding finicky, would a native speaker ever use 'must + present perfect' in this sense?