Read java props from env vars

build.sc

@@ -846,6 +846,11 @@ trait Cli extends SbtModule with ProtoBuildModule with CliLaunchers
     def runClasspath = T {
       super.runClasspath() ++ Seq(localRepoJar())
     }
+
+    // Required by the reflection usage in modules/cli/src/test/scala/cli/tests/SetupScalaCLITests.scala
+    override def forkArgs: T[Seq[String]] = T {
+      super.forkArgs() ++ Seq("--add-opens=java.base/java.util=ALL-UNNAMED")
+    }
   }
 }
 

modules/cli/src/main/scala/scala/cli/ScalaCli.scala

@@ -177,7 +177,7 @@ object ScalaCli {
       val jvmoptsLines          = jvmoptsContent.linesIterator.toSeq
       val (javaOpts, otherOpts) = jvmoptsLines.partition(_.startsWith("-D"))
       javaOpts.foreach { opt =>
-        opt.stripPrefix("-D").split("=", 2).match {
+        opt.stripPrefix("-D").split("=", 2) match {
           case Array(key, value) => System.setProperty(key, value)
           case _                 => System.err.println(s"Warning: Invalid java property: $opt")
         }
@@ -192,11 +192,23 @@ object ScalaCli {
       properties <- configDb.get(Keys.javaProperties).getOrElse(Nil)
     }
       properties.foreach { opt =>
-        opt.stripPrefix("-D").split("=", 2).match {
+        opt.stripPrefix("-D").split("=", 2) match {
           case Array(key, value) => System.setProperty(key, value)
           case _ => System.err.println(s"Warning: Invalid java property in config: $opt")
         }
       }
+
+    // load java properties from JAVA_OPTS and JDK_JAVA_OPTIONS environment variables
+    val javaOpts = sys.env.get("JAVA_OPTS").toSeq ++ sys.env.get("JDK_JAVA_OPTIONS").toSeq
+
+    javaOpts
+      .flatMap(_.split("\\s+"))
+      .foreach { opt =>
+        opt.stripPrefix("-D").split("=", 2) match {
+          case Array(key, value) => System.setProperty(key, value)
+          case _                 => // Ignore if not a Java property
+        }
+      }
   }
 
   private def main0(args: Array[String]): Unit = {

modules/cli/src/test/scala/cli/tests/SetupScalaCLITests.scala

@@ -2,12 +2,12 @@ package cli.tests
 
 import com.eed3si9n.expecty.Expecty.expect
 
-import java.util.Properties
+import java.util.{Collections, Properties}
 
 import scala.build.internal.Constants
 import scala.build.tests.TestInputs
 import scala.cli.ScalaCli
-import scala.util.Properties
+import scala.jdk.CollectionConverters.{MapHasAsJava, MapHasAsScala}
 
 class SetupScalaCLITests extends munit.FunSuite {
 
@@ -16,9 +16,9 @@ class SetupScalaCLITests extends munit.FunSuite {
     val value = "true"
     val inputs = TestInputs(
       os.rel / Constants.jvmPropertiesFileName ->
-        s"""-Xmx2048m
-           |-Xms128m
-           |-Xss8m
+        s"""-Xignored_1
+           |-Xignored_2
+           |-Xignored_3
            |-D$key=$value
            |""".stripMargin
     )
@@ -28,8 +28,48 @@ class SetupScalaCLITests extends munit.FunSuite {
       ScalaCli.loadJavaProperties(root)
       expect(sys.props.get(key).contains(value))
 
+      expect(sys.props.get("ignored_1").isEmpty)
+      expect(sys.props.get("ignored_2").isEmpty)
+      expect(sys.props.get("ignored_3").isEmpty)
       // restore original props
       System.setProperties(currentProps)
     )
   }
+
+  test(s"should read java properties from JAVA_OPTS and JDK_JAVA_OPTIONS") {
+    // Adapted from https://stackoverflow.com/a/496849
+    def setEnvVars(newEnv: Map[String, String]): Unit = {
+      val classes = classOf[Collections].getDeclaredClasses
+      val env     = System.getenv()
+      for (cl <- classes)
+        if (cl.getName.equals("java.util.Collections$UnmodifiableMap")) {
+          val field = cl.getDeclaredField("m")
+          field.setAccessible(true)
+          val obj = field.get(env)
+          val map = obj.asInstanceOf[java.util.Map[String, String]]
+          map.clear()
+          map.putAll(newEnv.asJava)
+        }
+    }
+
+    val javaOptsValues       = "  -Xignored_1   -Dhttp.proxy=4.4.4.4   -Xignored_2"
+    val jdkJavaOptionsValues = " -Xignored_3 -Dscala-cli=true  -Xignored_4"
+
+    TestInputs().fromRoot(root =>
+      //
+      val currentEnv = System.getenv().asScala.toMap
+      // modify environment variable of this process
+      setEnvVars(Map("JAVA_OPTS" -> javaOptsValues, "JDK_JAVA_OPTIONS" -> jdkJavaOptionsValues))
+      ScalaCli.loadJavaProperties(root)
+      expect(sys.props.get("http.proxy").contains("4.4.4.4"))
+      expect(sys.props.get("scala-cli").contains("true"))
+
+      expect(sys.props.get("ignored_1").isEmpty)
+      expect(sys.props.get("ignored_2").isEmpty)
+      expect(sys.props.get("ignored_3").isEmpty)
+      expect(sys.props.get("ignored_4").isEmpty)
+      // reset the env
+      setEnvVars(currentEnv)
+    )
+  }
 }