It was disabled in c6953d1ff6 because
a recent Nixpkgs bump brought in a new systemd which changed how
systemd-nspawn worked.
As far as I can tell, the issue was caused by this upstream systemd
commit:
b71a0192c0
Bind-mounting the host's `/sys` and `/proc` into the container's
`/run/host/{sys,proc}` fixes the issue and allows the test to succeed.
https://hydra.nixos.org/build/235888160
This is needed because Nixpkgs now contains dangling symlinks
(pkgs/test/nixpkgs-check-by-name/tests/symlink-invalid/pkgs/by-name/fo/foo/foo.nix).
This is broken because of a change in systemd in NixOS 23.05. It fails
with
Failed to mount proc (type proc) on /proc (MS_NOSUID|MS_NODEV|MS_NOEXEC ""): Operation not permitted
Previously, for tarball flakes, we recorded the original URL of the
tarball flake, rather than the URL to which it ultimately
redirects. Thus, a flake URL like
http://example.org/patchelf-latest.tar that redirects to
http://example.org/patchelf-<revision>.tar was not really usable. We
couldn't record the redirected URL, because sites like GitHub redirect
to CDN URLs that we can't rely on to be stable.
So now we use the redirected URL only if the server returns the
`x-nix-is-immutable` or `x-amz-meta-nix-is-immutable` headers in its
response.
