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Yann PETITJEAN for Doctolib Engineering

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Make rubocop 20x faster in 5 min

If you want to have your code formatted by rubocop without waiting for seconds, you are reading the right article.

At Doctolib, we have a lot of rubocop rules to keep our Ruby code readable by everyone.
But not everyone is familiar with all these rules, and fixing them by launching the rubocop script in the terminal can be a nightmare.

That’s why having the rubocop extension in VScode changes your life, you have immediate feedback of your errors, and it can automatically format the code for some rules.

Immediate feedback? 🤔 Not so immediate

I’ve peer coded with my colleague Lionel and I saw that he deactivated the auto format function for Ruby because it takes up to 4 seconds to save a simple file.

Rather than removing this super cool feature of VScode, I tried to find a way to make it faster.

And I found this gem which is underestimated in the Ruby community, and makes rubocop much faster rubocop-daemon

It’s 5 to 20 times faster to run rubocop

I made some speed tests on big files and the difference is breathtaking:

  • On the first save, it takes on average 2.7s with the normal rubocop for a file of 1K+ lines of code, and only 0.57s with the rubocop-daemon. It’s 5x faster!
  • Both tools are caching the file, so if you relaunch it for the same file, it will take 1.49s with the normal rubocop, and 0.07s with rubocop-daemon. It’s 20x faster!

It only takes 5 minutes to set up

1. Add the gem to the Gemfile of your project

gem 'rubocop-daemon', require: false

and launch

bundle install

Or if you don’t want to add it only on your computer, just launch:

gem install rubocop-daemon

2. Launch it

Each time you need it, start the server, run:

rubocop-daemon start

The rubocop server will run in the background until you switch off your computer.

3. Replace the rubocop command

Now, we want to replace the old command rubocop with the rubocop-daemon-wrapper, so you will be able to launch rubocop the same way as before.

curl -o /tmp/rubocop-daemon-wrapper
sudo mkdir -p /usr/local/bin/rubocop-daemon-wrapper
sudo mv /tmp/rubocop-daemon-wrapper /usr/local/bin/rubocop-daemon-wrapper/rubocop
sudo chmod +x /usr/local/bin/rubocop-daemon-wrapper/rubocop

We now need to add the command to our terminal.

Add this line at the end of your .zshrc or .bashrc file and save it.

export PATH="/usr/local/bin/rubocop-daemon-wrapper:$PATH"

Relaunch your terminal.

Last step: Override rubocop with a symlink to rubocop-daemon-wrapper

If you use rvm, run this command:

ln -fs /usr/local/bin/rubocop-daemon-wrapper $(which rubocop)

Or if you use rbenv:

ln -fs /usr/local/bin/rubocop-daemon-wrapper $(rbenv which rubocop)

And that’s it!

4. Configure VScode

You can now run rubocop as before, and VScode will use the fast rubocop.

Don’t forget to add the rubocop VScode extension if you don't have it.
And activate the “format on save” and “format on paste”:

Open preferences with cmd + , (or ctrl + ,)

Search for Format on save / Format on paste and activate them.

Ta-da, your code will be automagically formatted by rubocop at the lightning speed 🚀

Top comments (3)

fwuensche profile image
Flavio Wuensche • Edited

Hey Yann! I've been facing some issues with it locally.
If you want to rollback the changes you can:

unlink $(rbenv which rubocop)
gem install rubocop
source ~/.zshrc # or reload the terminal
# also reload your text editor if you're using an integrated linter
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muriloime profile image
Murilo Vasconcelos

you don't need rubocop extension anymore, as far as i can tell

harry_wood profile image

Yes. Looks like rubocop integrated rubocop-daemon functionality in v1.31 released June 2022: .

See "Server Mode" docs: