Test Scala 3 input/output with rule built against Scala 2.12

[bjaglin]

• Towards Scala 3 support scalafix#1316
• Requires Support Scala 3 in ScalafixTestkitPlugin sbt-scalafix#219
• Documented in Docs update for Scala 3 support in scalafix.g8 template scalafix#1410

This is moving the template from the built-in mutable/sequential crossScalaVersions way to the immutable/parallel sbt-projectmatrix one, to try to make it clearer that we test 3.x, but we don't cross-publish. For the record, here is the initial attempt without sbt-projectmatrix: 3ce2acf#diff-8b4a41b53e6e5f25138da6b4dc5f2d34051e59204e43fa2e9714a275997cf5e0 which mostly worked but was very hacky and hard to understand IMHO.

sbt:my-repo> projects
[info] In file:/home/bjaglin/git/projects/scalafix.g8/target/sbt-test/scalafix.g8-root/scripted/scalafix/
[info] 	   input2_11
[info] 	   input2_12
[info] 	   input2_13
[info] 	   input3
[info] 	   output2_11
[info] 	   output2_12
[info] 	   output2_13
[info] 	   output3
[info] 	 * my-repo
[info] 	   rules2_11
[info] 	   rules2_12
[info] 	   rules2_13
[info] 	   tests
[info] 	   testsTarget2_11
[info] 	   testsTarget2_12
[info] 	   testsTarget2_13
[info] 	   testsTarget3

I verified that

• the project can be imported in IntelliJ (2021.1)
• sbt ~tests/test is working
• +publishLocal publishes 3 artifacts

[bjaglin]

Moving back to draft while upstreaming changed made here to scalacenter/sbt-scalafix#219

[mlachkar]

I don't completely get why we have multiple rules modules. I think it can lead to thinking that to use write a scala 3 rule, you need to do it under rules_3 that doesn't exist.

[bjaglin]

I don't completely get why we have multiple rules modules.

That materializes what gets cross-built, it's common when moving from crossScalaVersions to https://github.com/sbt/sbt-projectmatrix.

I think it can lead to thinking that to use write a scala 3 rule, you need to do it under rules_3 that doesn't exist.

I went through several iterations to avoid that impression, and I thought the testsInput3 project was quite clear. It's the central point of using https://github.com/sbt/sbt-projectmatrix: testing 4 inputs with only 3 cross-built rules. Do you have any other idea?

[mlachkar]

I would like to have @adpi2 advice/review (if you can).
Maybe we can just put rules in 2.13, no crossVersion ?

[bjaglin]

As 3.x releases come out, we might want to test against different versions (although upgrading scala should not be as hard as on the 2.x era obviously). When/if that happens, we should use the full scala version as matrix suffixes, but I don't see a reason to do it now.

[bjaglin]

waiting for 0.9.28 to appear in https://search.maven.org/solrsearch/select?q=g:%22ch.epfl.scala%22+AND+a:%22sbt-scalafix%22&rows=10&wt=xml (https://github.com/foundweekends/giter8/blob/3c90ebedbf63be384a8673c11178c53767d85617/library/src/main/scala/giter8/MavenHelper.scala#L27) for the test to pass

[bjaglin]

waiting for 0.9.28 to appear in https://search.maven.org/solrsearch/select?q=g:%22ch.epfl.scala%22+AND+a:%22sbt-scalafix%22&rows=10&wt=xml (https://github.com/foundweekends/giter8/blob/3c90ebedbf63be384a8673c11178c53767d85617/library/src/main/scala/giter8/MavenHelper.scala#L27) for the test to pass

Still stale result from solr, so I ended up adding ee98b06 to unblock this for the release.