It seems as Python will be fetched from $PATH in Vim 8.1:
```
stat("/home/ma27/bin/python", 0x7ffe57a317b0) = -1 ENOENT (No such file or directory)
stat("/run/wrappers/bin/python", 0x7ffe57a317b0) = -1 ENOENT (No such file or directory)
stat("/home/ma27/.nix-profile/bin/python", 0x7ffe57a317b0) = -1 ENOENT (No such file or directory)
stat("/nix/var/nix/profiles/default/bin/python", 0x7ffe57a317b0) = -1 ENOENT (No such file or directory)
stat("/run/current-system/sw/bin/python", {st_mode=S_IFREG|0555, st_size=291, ...}) = 0
readlink("/run/current-system/sw/bin/python", "/nix/store/ggjkqbvwnv7dflkmdgmmp"..., 4096) = 72
```
This breaks in cases where you want to use a modified Python derivation
for the VIM plugins you use in `vim_configurable`:
```
let
vim_configurable' = vim_configurable.override {
# python with modules for ensime
python = python.withPackages (ps: with ps; [ sexpdata websocket_client ]);
};
in
vim_configurable'.customize {
# ...
}
```
With VIM 8.0 this worked perfectly fine, now it's necessary to install
the modified `python` in $PATH to actually use it, otherwise an error
like this arises:
```
[ensime] A dependency is missing, please `pip2 install sexpdata websocket-client` and restart Vim.
Press ENTER or type command to continue
```
However it should be possible to pass the modified Python to the
modules, the easiest workaround is to write a wrapper which prefixes
$PATH to have the Python derivation available.
Lots of packages are missing versions in their name. This adds them
where appropriate. These were found with this command:
$ nix-env -qa -f. | grep -v '\-[0-9A-Za-z.-_+]*$' | grep -v '^hook$'
See issue #41007.
Also rewrote the derivation for easier maintencence.
(And added @ysndr as maintainer for atom-beta, kind of an implicit
result of joining the two. If you're not okay with that, I'll patch
you out, but I'll presume consent.)
