Make scripted test run with Scala 2.13 by default

[Friendseeker]

Scala 2.13 is significantly more popular than Scala 2.12, hence it would cover more demographics for Zinc Scripted Test to run with 2.13 by default instead of 2.12.

scala/scala has scripted test running at 2.13, but ideally we catch 2.13 specific issue via Zinc CI directly, instead of relying on scala/scala CI.

[Friendseeker]

Two test failures revealed by this PR

• source-dependencies/compactify
• source-dependencies/compactify-nested

@dwijnand Would you mind to give it a quick look? Just want to know if these are false positives or not.

[dwijnand]

No, they're true positives. But only because as of 2.13.12 we use in-sources compiler bridges (scala/scala#10472) and the fix that is merged here (#1259) has been merged upstream (scala/scala#10542) but hasn't been released yet.

[lrytz]

@dwijnand are you sure we are using the binary bridge? Because IIUC that decision is not done by zinc, but by the build tool (https://github.com/sbt/sbt/blob/v1.9.7/zinc-lm-integration/src/main/scala/sbt/internal/inc/ZincLmUtil.scala#L93-L97).

In this case this would mean the scripted testing framework implementation within the zinc repo, no?

The two tests may be failing because -Xmax-classfile-name in 2.12 defaults to 255, but the setting was removed in 2.13 with a new default of 240 (scala/scala#7497).

This might be the reason for compactify-nested failing, @Friendseeker see https://github.com/scala/scala/blob/2.13.x/test/sbt-test/source-dependencies/compactify-nested/test for the 2.13 expected class file names.

Not sure about the compatcify test.

[Friendseeker]

Would it be better for defaultScalaVersion to be stored in sys.props instead?

e.g.

zinc/internal/compiler-bridge-test/src/test/scala/sbt/internal/inc/CompilingSpecification.scala

Lines 33 to 36 in 3e0ea93

	def scalaVersion =
	sys.props
	.get("zinc.build.compilerbridge.scalaVersion")
	.getOrElse(sys.error("zinc.build.compilerbridge.scalaVersion property not found"))

Then we can conveniently setup CI to run scripted tests against both 2.12 & 2.13 in a clean manner. Despite 2.12 is phasing out, it might be still worthy it to keep 2.12 coverage for the slim chance that some issue only surface in 2.12.

[Friendseeker]

@xuwei-k Since you did lots of work on the CI & Testing side, would you mind to give a quick look on this PR? Your opinion would be valuable.