December 31st, 1969

Perl-Based Neovim Plugins, part 1: Run Dat Service

Quite a few moons ago, I lusted for an easy way to write Vim plugins. For me easy means ”perl-based”, so I explored Vim’s API for its (optionally) embedded perl interpreter. That API is serviceable, but archaic. So that in turn lead to Vim::X, which aims to grease the vim/perl interfacing into the modern age.

Fast-forward a wee bit, and I discover neovim. One of the neat features of this new vi incarnation is an RPC interface allowing external programs to interact with the editor. That’s a paradigm change from the old Vim way. Whereas the Vim/Perl API tightly bind interpreter and editor together (I mean, the interpreter is compiled as part of the editor. You literally can’t get bound tighter than that), now plugins could be written as itsy-bitsy external services connecting to the editor and doing their things.

That promise of flexibility doesn’t come without a few drawbacks. An obvious one is the complexity of the interactions between the editor and the plugin services. Since those interactions now flow through a RPC channel, what were straight-up function calls now become the intricate asynchronous dance of requests and responses.

Totally new way of doing things. Twisted jungle of new technologies laid at our feet, and jagged details at the horizon. Well, you know me: I had to give it a whirl.

Once the post-whirling dust settled, I had written MsgPack::RPC — to generically interact with MsgPack-based RPC interfaces — Neovim::RPC — to interact with neovim instances — and a couple of blog entries — to interact with youses peeps.

Then the project went dormant, as I gamboled away to other wacky ventures. But I’ve picked it back recently, and brought quite a few changes to Neovim::RPC. Enough, I think, to warrant nothing less than a triology of blog entries.

In this first installment, beside blabbing about the project’s origin story I’ll show you how Neovim::RPC is expected to hook to a neovim instance. In the second part, we’ll see how simple plugins are written. And for the third part we’ll take a gander at a bigger, beefier plugin — namely, we’ll use neovim as a UI for Taskwarrior.

Run it: end-user edition

So, let’s get to the meat of it. You are an end-user. You just want to run Neomvim::RPC-based plugins. What do you need to do?

First, you need to install Neovim::RPC (like, duh). As I’m writing this, the new code for Neovim::RPC hasn’t been released to CPAN yet. It shouldn’t be long before I do it, but if you want to try it right now, it can be sneak-previewed in its GitHub repository.

Next, a few utility functions need to be added to your neovim configuration. I should (nay, will) wrap all of that in a proper vim configuration file, but for the time being dropping it straight into your ~/.config/nvim/init.vim would do the trick.

let g:nvimx_jobid = get(g:, 'nvimx_jobid', 0)

function! Nvimx_start()
    if !g:nvimx_jobid
        let g:nvimx_jobid = jobstart(['nvimx.pl', v:servername ])
        if !g:nvimx_jobid
            echo "could not start nvimx"

function! Nvimx_stop()
    if g:nvimx_jobid
        call jobstop( g:nvimx_jobid )
        let g:nvimx_jobid=0

function! Nvimx_restart()
    call Nvimx_stop()
    call Nvimx_start()

function! Nvimx_termstart()
    " we don't want two instances running...
    call Nvimx_stop()
    execute "terminal nvimx.pl " . v:servername

function! Nvimx_notify(...)
    call call( 'rpcnotify',  [g:nvimx_channel]  + a:000 )

function! Nvimx_request(...)
    call call( 'rpcrequest',  [g:nvimx_channel]  + a:000 )

call Nvimx_start()

Once this is done, you can run nvim and, tadah!, a Neovim::RPC minion should be gently running in the background, thanks to that final call Nvimx_start() in the config block. The function Nvimx_start starts a job running the script nvimx.pl, which is part of the Neovim::RPC’s distribution, and hooks it to the socket of the neovim instance, as given by v:servername.

Of course, since the off-the-shelf Neovim::RPC instance doesn’t do much we can only qualify its presence as being a… quiet one. The only plugin loaded by default is ‘LoadPlugin’. It usually allow us to tell Neovim::RPC to dynamically load plugins, but for this first run it’ll be used as a sign of life. We can use the vim function Nvimx_notify defined in the config block above to ask Neovim::RPC what’s up.

Run it: developer edition

As we can see in the previous section, by default Neovim::RPC doesn’t bother the neovim user with log messages. That’s usually a good thing, but when developing new plugins or debugging old ones, a little more noise would surely be appreciated.

You’ll be pleased to know that this is not a problem. We can simply shut down the too-silent Neovim::RPC instance and replace it by one run directly in a second terminal, where we’ll be able to see its logs in their glorious details.

Or… neovim actually boasts a in-editor terminal emulator, so instead of a second terminal, for bonus ouroboros points, we could have the editor run the terminal emulator running nvimx.pl that is going to connect back to the editor running it. That’s exactly what that Nvimx_termstart function does.

Coming up next

So far things aren’t terribly exciting. But now that we got the engine humming, in the next installment we’ll be able to get to business. Stay tuned!