Automated releases using gha-scala-library-release-workflow

[andrew-nowak]

@guardian/digital-cms

PR created by following steps in https://github.com/guardian/gha-scala-library-release-workflow/blob/main/docs/configuration.md

[rtyley]

Supporting older versions of Java

You'll probably want to add "-release:11" to the scalacOptions here:

pan-domain-authentication/build.sbt

Lines 20 to 25 in a679b56

	scalacOptions ++= Seq(
	"-feature",
	"-deprecation",
	// upgrade warnings to errors except deprecations
	"-Wconf:cat=deprecation:ws,any:e"
	),

This is because gha-scala-library-release-workflow runs with a very recent version of Java (eg Java 17, or soon Java 21 LTS), and by default this means your classes will be compiled for only that version of Java or above.

If you want pan-domain-authentication to work on app-servers running Java 11 - or even Java 8 (though I definitely don't recommend that!), you'll need to specify that in the build with the "-release:11" flag (see recommended sbt settings and eg here)

Artifact-producing - and non-artifact-producing - modules

The pre-existing use of publishArtifact is a bit confusing, and won't work well with the sbt-version-policy plugin:

pan-domain-authentication/build.sbt

Line 26 in a679b56

publishArtifact := false

It's confusing because it's set to false in commonSettings (implying that's a value setting that almost all sub-projects would want!), and then commonSettings is only used in a custom project() method which is used for some, but not all, of the sub-project definitions. To the outside observer, it's not obvious that using project() vs Project() will have that effect!

It won't work well with sbt-version-policy because the only flag that sbt-version-policy respects, when it's trying to work out whether it should download a previous version of an artifact for compatibility checking on a module, is publish / skip - so carefully applying publishArtifact := false in certain places isn't going to cut it!

If publish / skip isn't true, sbt-version-policy will assume that it needs to download a previous artifact for that module, and if that module doesn't actually publish artifacts, it will fail and crash the release (see scalacenter/sbt-version-policy#64).

There are only two projects that need publish / skip := true - the root project and exampleApp. Everything else can just have the default behaviour of publishing an artifact.

To try and make the confusing settings a bit clearer on other libraries, we're sometimes got rid of the name commonSettings etc, and instead used the name artifactProductionSettings, which has emphasised that the settings are only really required for sub-projects that actually produce artifacts.

[andrew-nowak]

@rtyley thanks, I think I've applied those suggestions now - we do still have dependents on java 8 (and I think Play 2.7) so will need it to stay JDK 8 compatible - I've set -release:8

I prefer commonSettings because it is common to all subprojects, including the example app which isn't destined to be published, so I've left it as that.

[rtyley]

Looks good to me!