Hello. I was repacking amdgpu-pro deb files and when I started converting licences, I have noticed that libdrm* packages have a MIT Licence text in copyright file. I decided to check if AUR/libdrm-git and Extra/libdrm uses MIT licence, but they don't. I contacted Lone_Wolf (maintainer of libdrm-git) and he said that he used a licence from Extra/libdrm. Should not it be changed to MIT instead of custom?
“MIT-style license” is a class of licenses, not a specific one. Each software using MIT-style licensing is having its own, independent license text. While in practice they may be nearly identical (modulo copyright line), they’re in fact separate licenses. The topic is discussed on the wiki: https://wiki.archlinux.org/index.php/Pkgbuild#license.
In particular the terms include: ------ The above copyright notice and this permission notice (including the next paragraph) shall be included in all copies or substantial portions of the Software. ------ Which means that if multiple MIT-licensed pieces of software are combined, the complete notice of each of them has to be included in the final work. And this is exactly what happens in case of libdrm: https://git.archlinux.org/svntogit/packages.git/tree/trunk/COPYING?h=packages/libdrm&id=b080357775c306e74a4257099ab4197604c4f57b.