Downgrading a package to removed version

Sometimes, an ebuild or specific package version which has been removed from the Gentoo ebuild repository might still be needed (ebuilds get removed as part of normal post-stabilization cleanups).

It can, for example, be useful to test an older version to report an issue to upstream, or to keep things working when there's problem with a newer version.

Steps

Fortunately, nothing is ever lost with Git. An ebuild can be pulled from the git history and placed into an ebuild repository to allow installation of a previously-removed package version.

Note
This tutorial will use sys-fs/zfs as an example.

First, create an ebuild repository ("overlay") locally, where the rescued ebuilds will be stashed, with eselect-repository (may need installation, see article):

root #eselect repository create local

Grab a git clone of the Gentoo repository and store it somewhere convenient, like /home/larry/git/gentoo:

user $git clone https://anongit.gentoo.org/git/repo/gentoo.git

If a clone already exists, update it:

user $git pull

It's helpful if the exact versions needed are known. In this case, suppose zfs-2.1.5.ebuild is needed.

Run git log to find the last commit before it was yanked:

user $git log -- sys-fs/zfs/zfs-2.1.5.ebuild

commit d429ef63a97180e28e18b6bcaea7ca338674e371
Author: Georgy Yakovlev <gyakovlev@gentoo.org>
Date:   Fri Sep 16 16:17:10 2022 -0700

    sys-fs/zfs: drop 2.1.5

    Signed-off-by: Georgy Yakovlev <gyakovlev@gentoo.org>

commit 2f3182056174dace67bb1cd7e4a5c08336a467a8
Author: Sam James <sam@gentoo.org>
Date:   Wed Jun 22 23:35:53 2022 +0100

    sys-fs/zfs: add 2.1.5

    Signed-off-by: Sam James <sam@gentoo.org>

In this case, d429ef63a97180e28e18b6bcaea7ca338674e371 is the commit which dropped sys-fs/zfs/zfs-2.1.5.ebuild, so d429ef63a97180e28e18b6bcaea7ca338674e371~1 refers to the last commit before it was dropped.

Tip
If needed (e.g. to get patches in sys-fs/zfs/files), the complete repository state can be obtained by running git checkout d429ef63a97180e28e18b6bcaea7ca338674e371~1 with no additional arguments.

Restore the ebuild:

user $git checkout d429ef63a97180e28e18b6bcaea7ca338674e371~1 sys-fs/zfs/zfs-2.1.5.ebuild

The required ebuild will now be present at sys-fs/zfs/zfs-2.1.5.ebuild.

Copy it to the repository called "local", created earlier:

root #mkdir -p /var/db/repos/local/sys-fs/zfs

root #cp -rv sys-fs/zfs/* /var/db/repos/local/sys-fs/zfs

Regenerate the Manifest (or use the same git checkout trick to recover the old one):

root #ebuild /var/db/repos/local/sys-fs/zfs/zfs-2.15.ebuild manifest

Once done, go back to the clone of gentoo.git and restore it to its original state:

root #git clean -fdx

root #git reset --hard origin/master

Emerge and enjoy!