Summary and Info:

The absence of this pacman feature makes it necessary to use/install sudo and edit sudoers file (which is unnecessary security risk for new users), only because you need to easily fetch the dependencies when you do work with AUR and ABS PKGBUILDS.

So makepkg -s is the only sane way to get the dependencies and requires sudo.

My suggestion is to implement a "pacman -P" for example that will automatically read the PKGBUILD of the parent directory, and parse them for syncing/installing.

An alternative solution (and probably more correct) would be to implement this to makepkg instead of pacman. Something like makepkg --onlyinstalldeps (-s right now is "also install deps") that would also disable the root check.

With this functionality a user should be able to install an AUR/ABS package like that without having sudo installed:

cd /(a PKGBUILD directory)/
su -c 'pacman -P' OR su -c 'makepkg --onlyinstalldeps'
makepkg


It is easy to write a small script to implement this, I just feel that a new user by default shouldn't have to install sudo and edit sudoers to effectively use makepkg.