Feature request: please automatically shorten last bar to fit with anacrusis

My first thought on this is that shortening the last bar automatically would cause confusion more than it would help. More often than not, people add measures to or delete measures from the end of the score to make it the correct length. Where would this measure end up? In the middle of the song or gone due to deletion.

On another note, while it is quite standard to have a bar at some point adjusted to account for the anacrusis it is not a universal practice. There are a number of songs with no such adjustment, though in my opinion there should be.

It is rare that all of the empty measures are laid out prior to entering scores unless the composer has predetermined the exact length of each section of the song. Since the measure would be altered before any notes are entered, MuseScore would need to have a way to mark the measure as altered so it can remember this. Basically you would end up with a non standard measure having no indication that it has been altered since each measure if filled with a measure rest that looks like all the rest.

There would end up being an abundance of posts on these forums wondering why a measure is the wrong length.

I'd say it is more or less intentional, for the reasons mike320 outlined.
I'm pretty sure this has been discussed here, but it was some years ago

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The reasons are indeed as stated, and then some. It would be difficult to guess what the user intends if he adds measures later (which probably happens 90% of the time). Also, section breaks. Also, the possibility for extreme confusion if someone did not want to use this convention. As mentioned, this particular convention - shortening the last measure to account for an anacrusis/pickup - is not universal, and in fact the majority of music in the world today does not use this convention. It was really intended only for short repeating forms like hymns or Baroque dance forms (minuet etc), so that the player could repeat the whole piece seamlessly without question about how to handle the turnaround. It is essentially not often used in longer pieces, or even in shorter pieces composed in the last century or two. And it clearly makes so sense at all in pieces that involve time signature changes - what would you do if the piece started in with a one-beat anacrusis in 4/4 but ended in 2/4?

So it's for all of these reasons that if you are creating music for which this particular convention makes sense, it also makes sense for you to apply it yourself.