If you are trying to compile libxml2 on a system that has limited outbound Internet connectivity which does not allow outbound connections to port 21, then you are unable to fetch the sources.
The sources however are fetchable via https as per:
which lists gitlab.gnome.org as optional download location:
"Libxml2 is also available from GIT:
See libxml2 Git web. To checkout a local tree use"
In the case of the latest version, the URL would be:
Steps to Reproduce:
Can fail to download via FTP and there is no alternative in the ebuild. Upstream https alternative does exist.
Attempt FTP download first, if this fails, try https download.
Note that I'd expect you to be using GENTOO_MIRRORS anyway, mirrors for which are available via HTTP and overn HTTPS. Upstream URLs aren't always reliable.
But sure, this seems preferable, thanks!
Hm. These aren't official distribution tarballs but instead generated by gitlab automatically. Mentioning you can checkout from git doesn't mean they endorse using gitlab to download the sources for distributions.
Such auto-generated tarballs are usually lacking files.