Downgrade the test-runner module dependency when it's added to the classpath for Scala >= 3.0.0 and < current Scala 3 LTS version

Author: Gedochao

modules/integration/src/test/scala/scala/cli/integration/RunTestsDefault.scala

@@ -189,8 +189,7 @@ class RunTestsDefault extends RunTestDefinitions
     }
 
   for {
-    scalaVersion <-
-      Constants.legacyScala3Versions.sorted.reverse.distinctBy(_.split('.').take(2).mkString("."))
+    scalaVersion <- TestUtil.legacyScalaVersionsOnePerMinor
     expectedMessage = "Hello, world!"
     expectedWarning =
       s"Defaulting to a legacy runner module version: ${Constants.runnerLegacyVersion}"

modules/integration/src/test/scala/scala/cli/integration/TestTestsDefault.scala

@@ -5,6 +5,7 @@ import com.eed3si9n.expecty.Expecty.expect
 import java.io.File
 
 import scala.cli.integration.Constants.munitVersion
+import scala.cli.integration.TestUtil.StringOps
 
 class TestTestsDefault extends TestTestDefinitions with TestDefault {
   test("Pure Java with Scala tests") {
@@ -62,11 +63,39 @@ class TestTestsDefault extends TestTestDefinitions with TestDefault {
     ).fromRoot { root =>
       val output = os.proc(TestUtil.cli, "test", extraOptions, ".", "--cross", "--power")
         .call(cwd = root).out.text()
-      def countOccurrences(a: String, b: String): Int =
-        if (b.isEmpty) 0 // Avoid infinite splitting
-        else a.sliding(b.length).count(_ == b)
       expect(output.contains(expectedMessage))
-      expect(countOccurrences(output, expectedMessage) == crossVersions.length)
+      expect(output.countOccurrences(expectedMessage) == crossVersions.length)
     }
   }
+
+  for {
+    scalaVersion <- TestUtil.legacyScalaVersionsOnePerMinor
+    expectedMessage = "Hello, world!"
+    expectedWarning =
+      s"Defaulting to a legacy test-runner module version: ${Constants.runnerLegacyVersion}"
+  }
+    test(s"run a simple test with Scala $scalaVersion (legacy)") {
+      TestInputs(os.rel / "example.test.scala" ->
+        // using JUnit to work around TASTy and macro incompatibilities
+        s"""//> using dep com.novocode:junit-interface:0.11
+           |import org.junit.Test
+           |
+           |class MyTests {
+           |  @Test
+           |  def foo(): Unit = {
+           |    assert(2 + 2 == 4)
+           |    println("$expectedMessage")
+           |  }
+           |}
+           |""".stripMargin).fromRoot { root =>
+        val res =
+          os.proc(TestUtil.cli, "test", ".", "-S", scalaVersion, TestUtil.extraOptions)
+            .call(cwd = root, stderr = os.Pipe)
+        val out = res.out.trim()
+        expect(out.contains(expectedMessage))
+        val err = res.err.trim()
+        expect(err.contains(expectedWarning))
+        expect(err.countOccurrences(expectedWarning) == 1)
+      }
+    }
 }

modules/integration/src/test/scala/scala/cli/integration/TestUtil.scala

@@ -27,6 +27,9 @@ object TestUtil {
   val cli: Seq[String]             = cliCommand(cliPath)
   val ltsEqualsNext: Boolean       = Constants.scala3Lts equals Constants.scala3Next
 
+  lazy val legacyScalaVersionsOnePerMinor: Seq[String] =
+    Constants.legacyScala3Versions.sorted.reverse.distinctBy(_.split('.').take(2).mkString("."))
+
   def cliCommand(cliPath: String): Seq[String] =
     if (isNativeCli)
       Seq(cliPath)
@@ -367,4 +370,10 @@ object TestUtil {
         Thread.sleep(200L)
         if (proc.isAlive()) proc.destroyForcibly()
       }
+
+  implicit class StringOps(a: String) {
+    def countOccurrences(b: String): Int =
+      if (b.isEmpty) 0 // Avoid infinite splitting
+      else a.sliding(b.length).count(_ == b)
+  }
 }

modules/options/src/main/scala/scala/build/Artifacts.scala

@@ -130,11 +130,32 @@ object Artifacts {
   ): Either[BuildException, Artifacts] = either {
     val dependencies = defaultDependencies ++ extraDependencies
 
+    val scalaVersion = (for {
+      scalaArtifactsParams <- scalaArtifactsParamsOpt
+      scalaParams  = scalaArtifactsParams.params
+      scalaVersion = scalaParams.scalaVersion
+    } yield scalaVersion).getOrElse(defaultScalaVersion)
+
+    val shouldUseLegacyRunners =
+      scalaVersion.startsWith("3") &&
+      scalaVersion.coursierVersion < s"$scala3LtsPrefix.0".coursierVersion
+
     val jvmTestRunnerDependencies =
-      if (addJvmTestRunner)
-        Seq(dep"$testRunnerOrganization::$testRunnerModuleName:$testRunnerVersion")
-      else
-        Nil
+      if addJvmTestRunner then {
+        val testRunnerVersion0 =
+          if shouldUseLegacyRunners then {
+            logger.message(
+              s"""$warnPrefix Scala $scalaVersion is no longer supported by the test-runner module.
+                 |$warnPrefix Defaulting to a legacy test-runner module version: $runnerLegacyVersion.
+                 |$warnPrefix To use the latest test-runner, upgrade Scala to at least $scala3LtsPrefix."""
+                .stripMargin
+            )
+            runnerLegacyVersion
+          }
+          else testRunnerVersion
+        Seq(dep"$testRunnerOrganization::$testRunnerModuleName:$testRunnerVersion0")
+      }
+      else Nil
 
     val jmhDependencies = addJmhDependencies.toSeq
       .map(version => dep"${Constants.jmhOrg}:${Constants.jmhGeneratorBytecodeModule}:$version")
@@ -408,15 +429,8 @@ object Artifacts {
               if runnerVersion.endsWith("SNAPSHOT") then
                 Seq(coursier.Repositories.sonatype("snapshots"))
               else Nil
-            val scalaVersion = (for {
-              scalaArtifactsParams <- scalaArtifactsParamsOpt
-              scalaParams  = scalaArtifactsParams.params
-              scalaVersion = scalaParams.scalaVersion
-            } yield scalaVersion).getOrElse(defaultScalaVersion)
             val runnerVersion0 =
-              if scalaVersion.startsWith("3") &&
-                scalaVersion.coursierVersion < s"$scala3LtsPrefix.0".coursierVersion
-              then {
+              if shouldUseLegacyRunners then {
                 logger.message(
                   s"""$warnPrefix Scala $scalaVersion is no longer supported by the runner module.
                      |$warnPrefix Defaulting to a legacy runner module version: $runnerLegacyVersion.