ExplicitResultTypes can't easily be used with projects using sbt-projectmatrix

[bjaglin]

As scalafixScalaBinaryVersion must be set at the ThisBuild level (say 2.13 for an example) and ExplicitResultTypes requires the binary version of each project to match the one used in Scalafix, an aggregating scalafixAll run will fail on 2.11 and 2.12 projects. There is no easy way in sbt-projectmatrix or sbt-scalafix to run scalafixAll only on 2.13 projects.

More generally, usage of sbt-projectmatrix with sbt-scalafix is non-optimal at best, dangerous at worst, as an aggregating scalafixAll runs rewrites across each axis in parallel. The same applies for scalafmt I believe.

[bjaglin]

Workaround:

scalafix/project/ScalafixBuild.scala

Lines 314 to 334 in b5230fd

	private def configSettings: Seq[Def.Setting[_]] = List(
	// Workaround for https://github.com/scalacenter/scalafix/issues/1592:
	// effectively skip scalafix[All] on 2.x projects not matching scalafixScalaBinaryVersion
	scalafix / unmanagedSources := {
	val prev = (scalafix / unmanagedSources).value
	if (
	Seq(scalafixScalaBinaryVersion.value, "3")
	.contains(scalaBinaryVersion.value)
	) {
	prev
	} else {
	Seq()
	}
	},
	scalafixConfig := {
	if (scalaBinaryVersion.value.startsWith("2"))
	Some(file(".scalafix-scala2.conf"))
	else
	Some(file(".scalafix-scala3.conf"))
	}
	)

[bjaglin]

Somewhat related: #1747

[bjaglin]

#1583 would solve this