Update Dec 19 : Whereas previously Oni was freely downloadable, there since appears to have been a change in project direction. The IDE is now called Onivim 2 and there is a pre-order fee. No idea if you can still install the version I used below, but the post might be useful in other contexts.

K&R’s Second Edition of the C Programming Language (*affiliate link) is not an easy read. To tame it I thought I might use Oni to do some of the heavy lifting, which is an IDE with Neovim as a back end. It looked pretty and was meant to work out of the box. I however spent an age getting it to do linting got C, so below are my struggles:

1. Install Oni.

So this is fairly straightforward. Head to their downloads page and install the deb package via Ubuntu Software. Easy enough but opening the application will get an error:“Uh oh! Unable to launch Neovim… Neovim v0.2.1 is required to run Oni.”

2. Install Neovim.

There are a number of ways to do this, the default one is to install an appimage. I’m hesitant about appimages; a good idea but not entirely sure how you are meant to update them. Instead elsewhere on the downloads page there is an Ubuntu Personal Package Archive (PPA). Unfortunately, at time of writing, the stable PPA isn’t at the current version, while the unstable version breaks Oni. To install the stable version of neovim:

sudo add-apt-repository ppa:neovim-ppa/stable

sudo apt update

sudo apt install neovim

This will get you a working version of Oni, but will not get you IDE features for C or C++.

3. Install clang.

This is where things get more complicated. Although Oni does work out of the box for languages such as JavaScript and HTML, it doesn’t for C or C++. Instead their language-support guidance tells you that you need clangd. Clangd leverages clang and is an implementation of the Language Server Protocol intended to “provide language ‘smartness’ features like code completion… for… C/C++ editors.” There are PPAs for both in Ubuntu that can be installed with:

sudo apt install clang

sudo apt install clang-tools

Although you might think this would do it - it doesn’t. When Oni initialises it expects to find clangd within the /usr/bin/ directory, however the name of the file the PPA installs is different: clangd-6.0 (referring to the version number). To solve this a symlink can be created referencing the expected file:

sudo update-alternatives --install /usr/bin/clangd clangd /usr/bin/clangd-6.0 1000

And wallah, Oni works for C and C++, almost out of the box… Interestingly once I had got it working it slowed to a crawl when you where looking at code longer than a hundred or so lines, so I abandoned it and went back to straight neovim.