sbt 2

build.sbt

@@ -8,6 +8,17 @@ name := "sbt-jshell"
 
 sbtPlugin := true
 
+crossScalaVersions += "3.3.4"
+
+pluginCrossBuild / sbtVersion := {
+  scalaBinaryVersion.value match {
+    case "2.12" =>
+      sbtVersion.value
+    case _ =>
+      "2.0.0-M2"
+  }
+}
+
 sbtPluginPublishLegacyMavenStyle := {
   sys.env.isDefinedAt("GITHUB_ACTION") || isSnapshot.value
 }

project/plugins.sbt

@@ -1,4 +1,5 @@
 Compile / unmanagedSourceDirectories += baseDirectory.value.getParentFile / "src" / "main" / "scala"
+Compile / unmanagedSourceDirectories += baseDirectory.value.getParentFile / "src" / "main" / "scala-2.12"
 
 scalacOptions ++= Seq(
   "-deprecation",

src/main/scala-2.12/sbtjshell/JShellCompat.scala

@@ -0,0 +1,20 @@
+package sbtjshell
+
+import sbt.{Configuration, Def, Task}
+import sbt.Keys.fullClasspath
+import java.io.File
+
+private[sbtjshell] trait JShellCompat { self: JShellPlugin.type =>
+  import self.autoImport.*
+
+  def jshellFullClasspath(c: Configuration): Def.Setting[?] = {
+    (c / jshell / fullClasspath) := {
+      (c / fullClasspath).value.filter(_.data.exists)
+    }
+  }
+
+  def jshellFullClasspathValue(c: Configuration): Def.Initialize[Task[Seq[File]]] =
+    Def.task(
+      (c / jshell / fullClasspath).value.map(_.data)
+    )
+}

src/main/scala-3/sbtjshell/JShellCompat.scala

@@ -0,0 +1,21 @@
+package sbtjshell
+
+import sbt.{Configuration, Def,  given }
+import sbt.Keys.fullClasspath
+import sbt.Keys.fileConverter
+
+private[sbtjshell] trait JShellCompat { self: JShellPlugin.type =>
+  import self.autoImport.*
+
+  def jshellFullClasspath(c: Configuration): Def.Setting[?] = {
+    (c / jshell / fullClasspath) := {
+      val converter = fileConverter.value
+      (c / fullClasspath).value.filter(x => converter.toPath(x.data).toFile.exists)
+    }
+  }
+
+  def jshellFullClasspathValue(c: Configuration) = Def.task{
+    val converter = fileConverter.value
+    (c / jshell / fullClasspath).value.map(x => converter.toPath(x.data).toFile)
+  }
+}

src/main/scala/sbtjshell/JShellPlugin.scala

@@ -2,12 +2,12 @@ package sbtjshell
 
 import javax.tools.Tool
 import java.util.ServiceLoader
-import sbt._
+import sbt.{_, given}
 import sbt.Keys._
 import sbt.complete.DefaultParsers._
 import scala.collection.JavaConverters._
 
-object JShellPlugin extends AutoPlugin {
+object JShellPlugin extends AutoPlugin with JShellCompat {
 
   object autoImport {
     val jshell = inputKey[Int]("invoke jshell")
@@ -30,14 +30,12 @@ object JShellPlugin extends AutoPlugin {
   override val projectSettings: Seq[Def.Setting[_]] = Def.settings(
     Seq(Compile, Test).flatMap { c =>
       Def.settings(
-        (c / jshell / fullClasspath) := {
-          (c / fullClasspath).value.filter(_.data.exists)
-        },
+        jshellFullClasspath(c),
         (c / jshell) := {
           val args = spaceDelimited("<arg>").parsed.toList
-          val path = (c / jshell / fullClasspath).value
-            .map(_.data.getCanonicalPath)
-            .mkString(System.getProperty("path.separator"))
+          val path = jshellFullClasspathValue(c).value
+            .map(_.getCanonicalPath)
+            .mkString(java.io.File.pathSeparator)
 
           IO.withTemporaryFile("jshell-startup", ".jsh") { temp =>
             val startup = (c / jshell / initialCommands).?.value match {