Travis CI Scala Play Application Build & Deployment Optimization - scala

Question

I have a project on GitHub where I'm using Travis CI for doing CI & CD. It is a Scala application built using sbt and runs as a web app using the Play framework. I have written the build pipeline such that I do the following as build stages:
jobs:
include:
- stage: test
script: sbt clean coverage test coverageReport
- stage: assemble-jar
script: sbt "set test in assembly := {}" assembly
if: branch = master
- stage: push-docker
script: bash docker_push.sh
if: branch = master
The problem that I face now is that during the test stage, it gets formatted and compiled once and so does it during the assembly and once again during the push-docker stage. This is quite annoying given the fact that how slow the Scala compiler is. Is there any way to optimize this such that it does not get compiled for every single stage? I did learn about caches and have the following as well in my yml:
cache:
directories:
- "$HOME/.ivy2/cache"
- "$HOME/.sbt"
But that unfortunately does not help as it caches only the dependencies but not the result of the previous build stage. What could I do to make it better?

Answer 1

First, you cannot really re-use the compiled class files of the test stage, since these have scoverage instrumentation embedded which makes them depend on scoverage at runtime. It will crash when you try to run without it.
Second, if you want to share build files between the assemble-jar and push-docker stages, you may use S3 to do so: https://docs.travis-ci.com/user/build-stages/share-files-s3/