Getting an old package will work for a while, but sooner or later dependencies will start to break and then you'll be back to square 1. At that point you'll need to rebuild it, and when that fails you'll need to start adding patches... and this is just one package. there's an increasing amount of slop in linux, including the kernel itself, i'm afraid if you have a purist attitude you're gonna want to start looking at other projects like freebsd.

Its a bit of a sidestep from pacman, but nix package manager can be installed on almost any Linux device, and you can pin dependencies to an exact git hash if you want (with flakes)

I have bad news for you: there are AI slop contributions in more than just the D compiler package. You're fighting an uphill battle.

I don't know anything about the D compiler specifically, but in general, pacman doesn't support partial system upgrades. If the package has no dependencies (or has very stable dependencies) you may be OK with the older package.

All that said, if you still have the old package, you can reinstall it with:

pacman -U /var/cache/pacman/pkg/<old_pkg_name>.pkg.tar.zst

You'll also have to add the package name to your IgnorePkg list in /etc/pacman.conf.

Open their git repo, find the commit where the version number was assigned, checkout the repo, build the the package per relevant instructions in the checked out readme, repeat the aforementioned steps as necessary to build any dependencies if necessary, rebuild the package after you've addressed all of the dependency issues, smile a smile of self satisfaction, avoid updates.

Go to archlinux archive, download required version (or look it up in local pacman cache), install it with pacman -U ..., add package to IgnorePkg in /etc/pacman.conf.

See here

Then if you want to lock that specific version, go to /etc/pacman.conf and add the base package name to the ignore list so it doesn't just go and get updated on the next upgrade run.