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C# Autocompletion in Emacs

Originally published here. Since LSP servers became a thing, the answer to all of this now is 'use eglot'.

Just a quickie. The family are in Cornwall, so I was going to take the opportunity to knock up some kind of C# autocompletion – intellisense is the only thing I miss from my days of working with Visual Studio (though it’s not enough to make me want to embrace the horrors of Monodevelop). I was intending on glueing SublimeText’s CompleteSharp binary into Emacs with a bit of elisp and unicorn dust when I noticed on Reddit that someone had created Omnisharp, which integrates NRefactory, the code analysis and completion backend for Monodevelop, into Vim. Rather splendidly, they’d implemented it via an frontend-agnostic http server, allowing other editors to call to use it.

When I originally checked there were integrations for Vim and SublimeText, so I started working out how to wrangle http POST requests in lisp, but by the end of the week I noticed that someone had beaten me to it and created the rather wonderful Omnisharp-Emacs. Fortune was on my side.

I’ve put in a bit of work integrating it with my preferred completion system, company-mode, and now the full glory of C# completion is mine. Couple of screenies:

autocompletion popup

Here you can see the popup menu with the relevant completions, and more detailed information in the minibuffer.

autocompletion parameters

And here we’ve selected a candidate and company-mode is allowing us to fill in the parameters by tabbing through them and typing in text.

The company-mode integration is sitting in a fork in github, and I’m hoping to get it pulled upstream soon.

Omnisharp has lots of other tricks too, such as showing help documentation, renaming variables, jumping to definitions and lots of other fun stuff. I’m probably going to be using this on a daily basis.

There is a minor downside to all this, which is that NRefactory works in terms of Mono/Visual Studio solution files and their associated project files, and I’ve moved my workflow entirely over to my own, Emacsy, concept of projects which doesn’t require manual registration of files and things like that. I don’t like having to add files manually, but nor do I like having two systems to maintain, so I’m going to have to work out a way of getting them to play nicely together.

Besides that, very minor, wrinkle, I’m a happy man, and I’m hugely grateful to the authors of Omnisharp, Omnisharp-Emacs and company-mode – all three are fantastic.

Which leaves the rest of the weekend free to decide whether to buy an Ergodox keyboard with Cherry Blues or Cherry Browns, and then I can wear my geek badge with pride.

UPDATE!

After a busy weekend of github-based collaboration, company-mode is now properly integrated into omnisharp-emacs. Head on over to the github page to have a look at the awesome features we’ve piled in – return type information, documentation buffers, tabbing through method parameters, smart completion detection, it’s all there.