electronjoe / zio_scala3_gitpod

ZIO Scala3 Template with VS Code Containers

This repository is a Github Template for ZIO library use in Scala 3. It uses VS Code Devcontainer configuration to support ~zero effort environmental setup with just two dependencies: Visual Studio Code with the Remote Container extension (somewhat a misnomer, can be local use also), and Docker. See below for details. Presently this template employs the following:

• hseeberger/scala-sbt with
  • OpenJDK 11.0.10
  • SBT 1.5.0
  • Scala 3.0.0-RC2
• ZIO 1.0.6

Big thank you to hseeberger/scala-sbt, whose scala-sbt Dockerfile I use as a basis for this Template (then layering on VS Code Remote Devcontainer support in this repo's Dockerfile).

Origin Story

With the release of Scala 3, and being very curious about the ZIO library, I wanted to explore and learn. I created this Template after having some trouble following the Scala 3 Getting Started options - ultimately I was successful but it was not a smooth experience. In my professional life I've found VS Code's Remote - Containers extension to be excellent for ~one-click environmental spin-up, minimal IDE support and and github repository integration. So I created a GH Template with this tool stack.

Using this Template

1. Create your own repo using this Template (Creating a repository from a template)
2. Install Visual Studio Code
3. Install Docker
4. Open Visual Studio Code and install the Remote - Containers extension
5. Hit F1 to get the Command Pallete and type `Remote-Containers: Clone Repository in Container Volume...'
6. Paste the URL of your Github repository into the box (e.g. https://github.com/electronjoe/zio_scala3_vscode_template but substitute your username and repo)
7. Hit enter, then when prompted select Create Unique Volume in Docker, hit enter
8. Now be patient, much has to happen. You should see a Starting Devcontainer Notification (you can click to monitor logs).
   1. VS Code will clone the repo into a Docker Mount
   2. VS Code will fetch the base Docker container (~600 MB github.com/hseeberger/scala-sbt)
   3. VS Code will use docker build to add VS code Container support
   4. VS Code will auto-install in container plugins incl Metals
9. Once the source code appears, you should be presented with a notification at bottom right New sbt workspace detected, would you like to import the build? -> Click Import build (click bell icon at bottom right if you missed it)
   1. At this point you can monitor progress View->Output and from the drop-down select Metals
   2. Be patient... very patient...
   3. sbt fetches dependencies, metals and boop get configured - you may see error messages in Metals Output, keep waiting
10. You will know all is complete when, if you open src/main/scala/Main.scala and click on e.g. the myAppLogic symbol a tooltip giving type information is displayed (val myAppLogic: zio.ZIO[Console, java.io.Exception, Unit])

You can test run Main.scala by opening a new terminal (Terminal -> New Terminal) and typing sbt run. You should observe:

vscode ➜ /workspaces/zio_scala3_starter (main ✗) $ sbt run
copying runtime jar...
[info] welcome to sbt 1.5.0-RC2 (Oracle Corporation Java 11.0.10)
[info] loading settings for project zio_scala3_starter-build-build from metals.sbt ...
[info] loading project definition from /workspaces/zio_scala3_starter/project/project
[info] loading settings for project zio_scala3_starter-build from metals.sbt ...
[info] loading project definition from /workspaces/zio_scala3_starter/project
[success] Generated .bloop/zio_scala3_starter-build.json
[success] Total time: 1 s, completed Apr 16, 2021, 10:38:00 AM
[info] loading settings for project root from build.sbt ...
[info] set current project to scala3-simple (in build file:/workspaces/zio_scala3_starter/)
[info] compiling 1 Scala source to /workspaces/zio_scala3_starter/target/scala-3.0.0-RC2/classes ...
[info] running MyApp 
Hello! What is your name?
scott
Hello, scott, welcome to ZIO!
[success] Total time: 33 s, completed Apr 16, 2021, 10:38:34 AM

Issues

It appears to me that Metals is re-downloading sbt and not using the sbt provided by the hseeberger/scala-sbt base Docker layer. This is incredibly inefficient and should be remedied.

Potential Future Work

Offer GraalVM native builds (github.com/hseeberger/scala-sbt has a docker build for this, but it is not in a favorable base OS for the VS Code devcontainer overlay conviguration - at least not in my experimentation so far).

docker run --mount source=.,target=/home/sbtuser -it --rm -u sbtuser -w /home/sbtuser hseeberger/scala-sbt:latest /bin/sh