When starting an older Emacs (23.4, say) for testing, I get an error from package initialisation a certain package is not available for installation. list-packages also shows a failure but with no details.
Starting with --debug-init shows that the error is:
(error "Archive location https://melpa.org/packages/ is not an absolute file name")
What causes this?
This misleading error is due to string-matching the URL against "http:" - essentially HTTPS is not supported by package-legacy.el.
Arguably this is also a bug in cask.el (which only uses HTTPS) but I'm not sure if they already dropped support for Emacs 23.
In my case, I still had a package.el in my emacs config from when I was using Emacs 23, and even now that I'm on Emacs 24 it was still using the "vendored" package.el. Deleting that file fixed my issue.
