Use jvm system version if Java Home is higher or equal 17

modules/build/src/main/scala/scala/build/internal/OsLibc.scala

@@ -5,7 +5,12 @@ import coursier.jvm.{JavaHome, JvmIndex}
 import java.io.IOException
 import java.nio.charset.Charset
 
-import scala.util.Try
+import scala.build.Positioned
+import scala.build.blooprifle.VersionUtil.parseJavaVersion
+import scala.build.internal.CsLoggerUtil.*
+import scala.build.options.BuildOptions
+import scala.util.control.NonFatal
+import scala.util.{Properties, Try}
 
 object OsLibc {
 
@@ -81,4 +86,41 @@ object OsLibc {
       s"${JavaHome.systemId}|$defaultJvm0"
   }
 
+  def javaHomeVersion(javaHome: Positioned[os.Path]): (Int, String) = {
+    val ext     = if (Properties.isWin) ".exe" else ""
+    val javaCmd = (javaHome.value / "bin" / s"java$ext").toString
+
+    val javaVersionOutput = os.proc(javaCmd, "-version").call(
+      cwd = os.pwd,
+      stdout = os.Pipe,
+      stderr = os.Pipe,
+      mergeErrIntoOut = true
+    ).out.text().trim()
+    val javaVersion = parseJavaVersion(javaVersionOutput).getOrElse {
+      throw new Exception(s"Could not parse java version from output: $javaVersionOutput")
+    }
+    (javaVersion, javaCmd)
+  }
+
+  def downloadJvm(jvmId: String, options: BuildOptions): String = {
+    implicit val ec = options.finalCache.ec
+    val javaHomeManager = options.javaHomeManager
+      .withMessage(s"Downloading JVM $jvmId")
+    val logger = javaHomeManager.cache
+      .flatMap(_.archiveCache.cache.loggerOpt)
+      .getOrElse(_root_.coursier.cache.CacheLogger.nop)
+    val command = {
+      val path = logger.use {
+        try javaHomeManager.get(jvmId).unsafeRun()
+        catch {
+          case NonFatal(e) => throw new Exception(e)
+        }
+      }
+      os.Path(path)
+    }
+    val ext     = if (Properties.isWin) ".exe" else ""
+    val javaCmd = (command / "bin" / s"java$ext").toString
+    javaCmd
+  }
+
 }

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

@@ -13,15 +13,13 @@ import java.nio.charset.StandardCharsets
 import java.security.MessageDigest
 
 import scala.build.EitherCps.{either, value}
-import scala.build.blooprifle.VersionUtil.parseJavaVersion
 import scala.build.errors._
 import scala.build.internal.Constants._
 import scala.build.internal.CsLoggerUtil._
 import scala.build.internal.ScalaParse.scala2NightlyRegex
 import scala.build.internal.{OsLibc, StableScalaVersion, Util}
 import scala.build.options.validation.BuildOptionsRule
 import scala.build.{Artifacts, Logger, Os, Position, Positioned}
-import scala.util.Properties
 import scala.util.control.NonFatal
 
 final case class BuildOptions(
@@ -162,20 +160,8 @@ final case class BuildOptions(
   case class JavaHomeInfo(javaCommand: String, version: Int)
 
   private lazy val javaCommand0: Positioned[JavaHomeInfo] = {
-    val javaHome = javaHomeLocation()
-    val ext      = if (Properties.isWin) ".exe" else ""
-    val javaCmd  = (javaHome.value / "bin" / s"java$ext").toString
-
-    val javaVersionOutput = os.proc(javaCmd, "-version").call(
-      cwd = os.pwd,
-      stdout = os.Pipe,
-      stderr = os.Pipe,
-      mergeErrIntoOut = true
-    ).out.text().trim()
-    val javaVersion = parseJavaVersion(javaVersionOutput).getOrElse {
-      throw new Exception(s"Could not parse java version from output: $javaVersionOutput")
-    }
-
+    val javaHome               = javaHomeLocation()
+    val (javaVersion, javaCmd) = OsLibc.javaHomeVersion(javaHome)
     Positioned(javaHome.positions, JavaHomeInfo(javaCmd, javaVersion))
   }
 

modules/cli/src/main/scala/scala/cli/commands/SharedOptions.scala

@@ -12,7 +12,6 @@ import java.io.{ByteArrayOutputStream, File, InputStream}
 
 import scala.build.blooprifle.BloopRifleConfig
 import scala.build.compiler.{BloopCompilerMaker, ScalaCompilerMaker, SimpleScalaCompilerMaker}
-import scala.build.internal.CsLoggerUtil._
 import scala.build.internal.{Constants, OsLibc}
 import scala.build.options.{Platform, ScalacOpt, ShadowingSeq}
 import scala.build.{options => bo, _}
@@ -189,31 +188,22 @@ final case class SharedOptions(
 
   def bloopRifleConfig(): BloopRifleConfig = {
 
-    val options     = buildOptions(false, None)
-    implicit val ec = options.finalCache.ec
-    val jvmId = compilationServer.bloopJvm.getOrElse {
-      OsLibc.baseDefaultJvm(OsLibc.jvmIndexOs, "17")
-    }
-    val javaHomeManager = options.javaHomeManager
-      .withMessage(s"Downloading JVM $jvmId")
-    val logger = javaHomeManager.cache
-      .flatMap(_.archiveCache.cache.loggerOpt)
-      .getOrElse(_root_.coursier.cache.CacheLogger.nop)
-    val command = {
-      val path = logger.use {
-        try javaHomeManager.get(jvmId).unsafeRun()
-        catch {
-          case NonFatal(e) => throw new Exception(e)
-        }
+    val options = buildOptions(false, None)
+    lazy val defaultJvmCmd =
+      OsLibc.downloadJvm(OsLibc.baseDefaultJvm(OsLibc.jvmIndexOs, "17"), options)
+    val javaCmd = compilationServer.bloopJvm.map(OsLibc.downloadJvm(_, options)).orElse {
+      for (javaHome <- options.javaHomeLocationOpt()) yield {
+        val (javaHomeVersion, javaHomeCmd) = OsLibc.javaHomeVersion(javaHome)
+        if (javaHomeVersion >= 17) javaHomeCmd
+        else defaultJvmCmd
       }
-      os.Path(path)
-    }
-    val ext = if (Properties.isWin) ".exe" else ""
+    }.getOrElse(defaultJvmCmd)
+
     compilationServer.bloopRifleConfig(
       logging.logger,
       coursierCache,
       logging.verbosity,
-      (command / "bin" / s"java$ext").toString,
+      javaCmd,
       directories.directories,
       Some(17)
     )