Don't set the `rtp` attribute using `overrideAttrs`. `overrideAttrs`
passes the attribute to the builder hence creates a different
derivation. This made vim plugins being built twice.
Neovim plugins are now more often than not written in lua.
One advantage of the lua ecosystem over vim's is the existence of
luarocks and the rockspec format, which allows to specify a package
dependencies formally.
I would like more neovim plugins to have a formal description,
"rockspec" being the current candidate.
This MR allows to use nix lua packages as neovim plugins, so as to enjoy
every benefit that rockspecs bring:
- dependdency discovery
- ability to run test suite
- luarocks versioning
- rockspec metadata
the vim update.py script will check if an attribute with the vim plugin
pname exists in lua51Packages. If it does, it uses
buildNeovimPluginFrom2Nix on it, which modifies the luarocks config to
do an almost flat install (luarocks will install the package in the lua
folder instead of share/5.1/lua etc).
It also calls toVimPlugin on it to get all the vim plugin niceties.
The list of packages that could benefit from this is available at
https://luarocks.org/labels/neovim
but I hope it grows.
