Wrapping up work on the RLS for GSoC

Work summary

It’s time to wrap up the work done on the Rust Language Server (RLS) for this year’s edition of Google Summer of Code. Time surely flew fast since the first blog post!

In general, the goal of the project was to improve the user experience and IDE support story for Rust. Apart from the regular bugfixes and QoL changes, the primary goal and biggest in terms of scope feature was to implement supporting multiple package targets and packages in general, including Cargo workspaces. Another one, a stretch goal of sorts, was to implement previewing macro expansion in the editor, however, in the end, there was not enough time to pursue that.

At the time of writing, the workspace support has been implemented (still requires more polishing), I managed to land 30 PRs for the RLS, push 50 commits (+2,837 insertions and -1,301 deletions) in total.

Additionally, my talk regarding the RLS and my work on it has been accepted for RustFest Zürich 2017! It’s titled “Teaching an IDE to understand Rust” and I’m looking forward to present it on September 30th!

Work done for multiple packages and workspaces

For supporting multiple crate targets, one of the most useful implemented features is ability to specify which target ([lib] or which [[bin]]) should be analyzed by the RLS, as well as supporting analyzing bin targets that require the lib from the same package. Additionally, the RLS itself can now detect which target should be analyzed, if the user didn’t explicitly specify it in the configuration.

Furthermore, a new workspace_mode has been added. When under it, the RLS doesn’t panic anymore when analyzing Cargo workspaces and happily provides all the diagnostic data from the compiler for all the packages inside (assuming files are saved on the disk), if a specific package hasn’t been explicitly specified by the user via the analyze_package option.

The work for workspace support was split into 3 stages:

  1. First one was to introduce a new, separate mode, under which the RLS would not crash and provide very basic diagnostics.
  2. Second one was to improve both the performance and support by executing the linked compiler and gathering diagnostics and analysis data, which drives the IDE features such as goto def, from every package in the workspace.
  3. Third one, the biggest, was to create and store a dependency graph of units of work (compiler calls), which would allow to improve the latency of the analysis and provide support for in-memory modified files.

As of now, all three stages are completed. The last one is still being polished - a concrete area of improvement is the accuracy of determination which changed files require a rebuild of which packages, as well as reliability of gathering provided analysis for multiple packages.

GSoC Experiences


One of the things I struggled the most with was prioritisation of the work I was tasked with. Even though the planned work was clearly defined, I tried to find a balance between doing the work on a bigger, planned feature and implementing smaller QoL changes or fixes that did ease/allow some people usage of the RLS. In the end, I found myself frequently working on the side tasks longer than I should’ve, effectively delaying the main job I was tasked with in the first place.

Having more freedom over one’s work is both good and bad. There are no strict dreadlines looming over you, however it’s easy to lose yourself if you don’t organize your own work yourself. When working on some side projects I sometimes used organization tools such as Trello or good ol’ Post-Its and in the end, I think I should’ve used it for this project. I managed to do most of the planned work, but I think this would allow me to focus better on the task at hand and better prioritise the work.

I very much feel like this is the area I need to improve on the most.


Before I started working on an open source project, it seemed really daunting to contribute to one. I’m not sure what’s causing this, maybe it’s stories about traditional open source projects’ core developers posting rants or aggressively rejecting contributions.

However it turns out the open source community is very welcoming and helpful. I think I’ve been bitten by the OSS bug by now and definitely find myself contributing also to other projects thanks to working on one during the Google Summer of Code.

I also have to give a shout out to the Rust community specifically here. When posting issues, asking (sometimes silly) questions on the IRC or getting some required features in Cargo for the RLS, people were always open and helpful every step of the way.

Speaking from a contributor’s perspective, it means a lot when people take their time to slow down and thoroughly explain as to why and how certain things work the way they do, so I’m really grateful for that. It encourages further contribution and makes you feel even better when doing that! After all, the work is not only useful to yourself, but also to other people in general.

I also learned quite a lot on how IDEs may be structured and how they interact with other tools/systems, most notably the compiler and a build system, to provide the desired functionality. Previously I treated it as a black box, where it performed some arcane compiler invocations and everything Just Worked™. Now that I had the occasion to work on one, it helped demistify the way a compiler and an IDE may work, both in general and in tandem. As it turns out, IDEs are not as complex as I thought and working on them was really interesting and accessible at the same time.

Closing words

Google Summer of Code turned out to be a wonderful experience. It changed the way I think about the open source movement and it opened it up for me somehow. Professionally, it also helped me grow as a programmer, both in terms of skill and communication required to do the job.

Furthermore, it helped me connect to and work with a lot of creative, capable people that are smarter than me. Here, I’d like to especially give a shout out to @nrc, Nick Cameron, who was a great mentor during this project, perfectly guided me through it and managed to put up with me! :smile:

If you may be thinking whether to apply for the next year’s edition of Google Summer of Code 2018, do it! I can wholeheartedly recommend it.

The GSoC project may be coming to an end, but there’s so much more that can be done for the RLS and Rust in general! Working on it is a joy and I’m probably here to stay. See you over at the RLS repo and related, stay tuned! :sunglasses:

Most notable PRs

Supporting multiple packages and targets
Smaller features and bugfixes
Refactoring / project organization