improvement: Set fork to true automatically for Scala 3

src/main/scala/scoverage/ScoverageSbtPlugin.scala

@@ -83,7 +83,7 @@ object ScoverageSbtPlugin extends AutoPlugin {
         case _         => defaultScoverageVersion
       }
     }
-  ) ++ coverageSettings ++ scalacSettings
+  ) ++ coverageSettings ++ scalacSettings ++ coverageTestRuntimeSettings(Test)
 
   private def isScala2(scalaVersion: String) =
     CrossVersion
@@ -203,9 +203,6 @@ object ScoverageSbtPlugin extends AutoPlugin {
         coverageEnabled.value && isScala3SupportingScoverage(scalaVersion.value)
       ) {
         Seq(
-          Some(
-            s"-coverage-out:${new java.io.File(coverageDataDir.value, "scoverage-data").getAbsolutePath}"
-          ),
           excludedPackages
             .collect {
               case v
@@ -234,6 +231,16 @@ object ScoverageSbtPlugin extends AutoPlugin {
     }
   )
 
+  // See https://github.com/scoverage/sbt-scoverage/issues/522
+  private def coverageTestRuntimeSettings(
+      config: Configuration
+  ): Seq[Setting[_]] =
+    Seq(
+      config / fork := coverageEnabled.value && isScala3SupportingScoverage(
+        scalaVersion.value
+      )
+    )
+
   private def scalacRuntime(deps: Seq[ModuleID]): String = {
     scalacRuntimeArtifact + optionalScalaJsSuffix(deps)
   }

src/sbt-test/scoverage/scala3-repeat-coverage/build.sbt

@@ -0,0 +1,14 @@
+version := "0.1"
+
+scalaVersion := "3.9.0"
+
+libraryDependencies += "org.scalameta" %% "munit" % "1.0.1" % Test
+
+coverageMinimumStmtTotal := 100
+coverageMinimumBranchTotal := 100
+coverageMinimumStmtPerPackage := 100
+coverageMinimumBranchPerPackage := 100
+coverageMinimumStmtPerFile := 100
+coverageMinimumBranchPerFile := 100
+
+coverageFailOnMinimum := true

src/sbt-test/scoverage/scala3-repeat-coverage/project/plugins.sbt

@@ -0,0 +1,9 @@
+val pluginVersion = sys.props.getOrElse(
+  "plugin.version",
+  throw new RuntimeException(
+    """|The system property 'plugin.version' is not defined.
+       |Specify this property using the scriptedLaunchOpts -D.""".stripMargin
+  )
+)
+
+addSbtPlugin("org.scoverage" % "sbt-scoverage" % pluginVersion)

src/sbt-test/scoverage/scala3-repeat-coverage/src/main/scala/GoodCoverage.scala

@@ -0,0 +1,7 @@
+object GoodCoverage {
+
+  def sum(num1: Int, num2: Int) = {
+    if (0 == num1) num2 else if (0 == num2) num1 else num1 + num2
+  }
+
+}

src/sbt-test/scoverage/scala3-repeat-coverage/src/main/scala/two/GoodCoverage.scala

@@ -0,0 +1,9 @@
+package two
+
+object GoodCoverage {
+
+  def sum(num1: Int, num2: Int) = {
+    if (0 == num1) num2 else if (0 == num2) num1 else num1 + num2
+  }
+
+}

src/sbt-test/scoverage/scala3-repeat-coverage/src/test/scala/GoodCoverageSpec.scala

@@ -0,0 +1,17 @@
+import munit.FunSuite
+
+class GoodCoverageSpec extends FunSuite {
+
+  test("GoodCoverage should sum two numbers") {
+    assertEquals(GoodCoverage.sum(1, 2), 3)
+    assertEquals(GoodCoverage.sum(0, 3), 3)
+    assertEquals(GoodCoverage.sum(3, 0), 3)
+  }
+
+  test("two.GoodCoverage should sum two numbers") {
+    assertEquals(two.GoodCoverage.sum(1, 2), 3)
+    assertEquals(two.GoodCoverage.sum(0, 3), 3)
+    assertEquals(two.GoodCoverage.sum(3, 0), 3)
+  }
+
+}

src/sbt-test/scoverage/scala3-repeat-coverage/test

@@ -0,0 +1,18 @@
+# https://github.com/scoverage/sbt-scoverage/issues/522
+# Scala 3 coverage in a single sbt session used to report 0% after the first
+# `clean; coverage; test` because measurement files were not rewritten.
+> clean
+> coverage
+> test
+> coverageReport
+$ exists target/scala-3.5.0/scoverage-data
+> clean
+> coverage
+> test
+> coverageReport
+$ exists target/scala-3.5.0/scoverage-data
+# coverage stays enabled; a third clean/test cycle should still record coverage
+> clean
+> test
+> coverageReport
+$ exists target/scala-3.5.0/scoverage-data