Migrate from sbt-crossproject to sbt-projectmatrix

Replace sbt-scala-native-crossproject with sbt-projectmatrix (0.11.0),
matching the convention used in other SoftwareMill projects (sttp, sttp-model).

Source layout changes:
- core/shared/src/ → core/src/main/scala/, core/src/test/scala/
- core/jvm/src/ → core/src/main/scalajvm/, core/src/test/scalajvm/
- core/native/src/ → core/src/main/scalanative/, core/src/test/scalanative/

Project names: core3 (JVM), coreNative3 (Native), examples3, examplesNative3.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: adamw

build.sbt

@@ -2,12 +2,13 @@ import com.softwaremill.SbtSoftwareMillCommon.commonSmlBuildSettings
 import com.softwaremill.Publish.{ossPublishSettings, updateDocs}
 import com.softwaremill.UpdateVersionInDocs
 import com.typesafe.tools.mima.core.{MissingClassProblem, ProblemFilters}
-import sbtcrossproject.CrossPlugin.autoImport.{crossProject, CrossType}
 import scalanative.build._
 
+lazy val scala3 = "3.3.7"
+
 lazy val commonSettings = commonSmlBuildSettings ++ ossPublishSettings ++ Seq(
   organization := "com.softwaremill.ox",
-  scalaVersion := "3.3.7",
+  scalaVersion := scala3,
   updateDocs := Def.taskDyn {
     val files1 = UpdateVersionInDocs(sLog.value, organization.value, version.value)
     Def.task {
@@ -52,50 +53,53 @@ compileDocumentation := {
 lazy val rootProject = (project in file("."))
   .settings(commonSettings)
   .settings(publishArtifact := false, name := "ox")
-  .aggregate(core.jvm, core.native, kafka, mdcLogback, flowReactiveStreams, cron, otelContext)
+  .aggregate(core.projectRefs ++ examples.projectRefs ++ Seq[ProjectReference](kafka, mdcLogback, flowReactiveStreams, cron, otelContext): _*)
 
-lazy val core = crossProject(JVMPlatform, NativePlatform)
-  .crossType(CrossType.Full)
-  .in(file("core"))
+lazy val core = (projectMatrix in file("core"))
   .settings(commonSettings)
   .settings(
     name := "core",
-    libraryDependencies += "org.scalatest" %%% "scalatest" % "3.2.20" % Test,
-    Test / fork := true
+    libraryDependencies += "org.scalatest" %%% "scalatest" % "3.2.20" % Test
   )
-  .jvmSettings(
-    libraryDependencies ++= Seq(
-      "com.softwaremill.jox" % "channels" % "1.1.2",
-      "org.apache.pekko" %% "pekko-stream" % "1.6.0" % Test,
-      "org.reactivestreams" % "reactive-streams-tck-flow" % "1.0.4" % Test
+  .jvmPlatform(
+    scalaVersions = Seq(scala3),
+    settings = enableMimaSettings ++ Seq(
+      Test / fork := true,
+      libraryDependencies ++= Seq(
+        "com.softwaremill.jox" % "channels" % "1.1.2",
+        "org.apache.pekko" %% "pekko-stream" % "1.6.0" % Test,
+        "org.reactivestreams" % "reactive-streams-tck-flow" % "1.0.4" % Test
+      )
     )
   )
-  .jvmSettings(enableMimaSettings)
-  .nativeSettings(
-    Test / fork := false,
-    // Only include native-specific tests; shared Ox tests use JVM-only APIs (java.time, java.net, etc.)
-    Test / unmanagedSourceDirectories := Seq((Test / sourceDirectory).value / "scala"),
-    nativeConfig ~= {
-      _.withMultithreading(true)
-    }
+  .nativePlatform(
+    scalaVersions = Seq(scala3),
+    settings = Seq(
+      Test / fork := false,
+      // Only include native-specific tests; shared Ox tests use JVM-only APIs (java.time, java.net, etc.)
+      Test / unmanagedSourceDirectories := Seq((Test / sourceDirectory).value / "scalanative"),
+      nativeConfig ~= { _.withMultithreading(true) }
+    )
   )
 
-lazy val examples = crossProject(JVMPlatform, NativePlatform)
-  .crossType(CrossType.Pure)
-  .in(file("examples"))
+lazy val examples = (projectMatrix in file("examples"))
   .settings(commonSettings)
   .settings(
     name := "examples",
     publishArtifact := false,
     Compile / mainClass := Some("VirtualThreadsNativeJvmBenchmark")
   )
-  .jvmSettings(
-    assembly / assemblyJarName := "examples-assembly.jar"
+  .jvmPlatform(
+    scalaVersions = Seq(scala3),
+    settings = Seq(
+      assembly / assemblyJarName := "examples-assembly.jar"
+    )
   )
-  .nativeSettings(
-    nativeConfig ~= {
-      _.withMultithreading(true)
-    }
+  .nativePlatform(
+    scalaVersions = Seq(scala3),
+    settings = Seq(
+      nativeConfig ~= { _.withMultithreading(true) }
+    )
   )
   .dependsOn(core)
 
@@ -113,7 +117,7 @@ lazy val kafka: Project = (project in file("kafka"))
       scalaTest
     )
   )
-  .dependsOn(core.jvm)
+  .dependsOn(core.jvm(scala3))
 
 lazy val mdcLogback: Project = (project in file("mdc-logback"))
   .settings(commonSettings)
@@ -124,7 +128,7 @@ lazy val mdcLogback: Project = (project in file("mdc-logback"))
       scalaTest
     )
   )
-  .dependsOn(core.jvm)
+  .dependsOn(core.jvm(scala3))
 
 lazy val flowReactiveStreams: Project = (project in file("flow-reactive-streams"))
   .settings(commonSettings)
@@ -135,7 +139,7 @@ lazy val flowReactiveStreams: Project = (project in file("flow-reactive-streams"
       scalaTest
     )
   )
-  .dependsOn(core.jvm)
+  .dependsOn(core.jvm(scala3))
 
 lazy val cron: Project = (project in file("cron"))
   .settings(commonSettings)
@@ -146,7 +150,7 @@ lazy val cron: Project = (project in file("cron"))
       scalaTest
     )
   )
-  .dependsOn(core.jvm % "test->test;compile->compile")
+  .dependsOn(core.jvm(scala3) % "test->test;compile->compile")
 
 lazy val otelContext: Project = (project in file("otel-context"))
   .settings(commonSettings)
@@ -157,7 +161,7 @@ lazy val otelContext: Project = (project in file("otel-context"))
       scalaTest
     )
   )
-  .dependsOn(core.jvm % "test->test;compile->compile")
+  .dependsOn(core.jvm(scala3) % "test->test;compile->compile")
 
 lazy val documentation: Project = (project in file("generated-doc")) // important: it must not be doc/
   .enablePlugins(MdocPlugin)
@@ -175,7 +179,7 @@ lazy val documentation: Project = (project in file("generated-doc")) // importan
     libraryDependencies ++= Seq(logback % Test)
   )
   .dependsOn(
-    core.jvm,
+    core.jvm(scala3),
     kafka,
     mdcLogback,
     flowReactiveStreams,