mill-buildr: Splitting large build.sc files into an scala project itself.

[vic]

At work we've been using mill since about late 2018 and never looked back!. Thanks to all people who have made of mill an awesome tool.

Our build.sc which was initially tiny grew a lot of modules over time (all in a mono-repo, eg, models, daos, remote-services, web-server, etc). About two years ago we started splitting our build.sc into smaller modules (other $file importable .sc files) and mill always worked fine but the ".sc editing" experience was not that good even using IntelliJ, they certainly looked like scala files but not-so-experienced developers were missing auto-completion and jump-to-definition features from their IDE. At the time I believe there was no bsp integration and all we had was GenIdea, but IntelliJ was not very good at finding references over lots of .sc files.

So, it was really important for me to make code on our "build-definitions" editable by anyone on the team. Have them use their IDE with all features while editing our build project, just like editing any other mill-scala project.

Trying to find a solution for this, I found a hack (we have been using this since about ~2020 and finally extracted the code to share with other people). The trick is, define a buildr project which has all our modules definitions as traits (a regular mill-scala project) and then load the runClasspath into the mill's interp runtime. After that, all build.sc file does is just create top level objects, basically just a list of objects extending their particular module implementations. This way the build.sc keeps small and clean and all the meat is in the buildr project.

So, this BuildrModule can be seen more as a pattern than a library, anyways, just shared a repo if other people having huge mill-projects can benefit from this idea:

https://github.com/vic/mill-buildr

(see the example build.sc and example buildr/src/*.scala on the repo)

[vic]

as a totally unrelated side note: we do have a picture of @lihaoyi at work to bless all our developments. his awesome libraries and book has helped us a lot to get over the difficult times.

[vic]

The lengend reads:
"This home is lihaoyi-ist, we don't take propaganda from other languages without types."
and
"Read my messages in the code, there is the truth - lihaoyi, 2018"

[lefou]

I remember that we discussed something like this in the chats. Nice it worked out for you. And thank you for sharing!

In the meantime, I experimented with using directives as comments, which are use by Scala CLI project. Turns out, they are very nice to declare plugin dependencies and source-includes. And in that experiment, I was also able to include and compile classic scala files to be used in Mill projects. My time is currently limited to continue on that, but I think that's the direction I most likely want to follow in upcoming Mill milestones.