Log a warning when invalid java properties are being passed to JAVA_OPTS or JDK_JAVA_OPTIONS env vars (#2843)

Author: Gedochao

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

@@ -184,7 +184,7 @@ object ScalaCli {
       }
       if otherOpts.nonEmpty then
         System.err.println(
-          s"Warning: Only java properties are supported in .scala-jvmopts file. Other options are ignored: ${otherOpts.mkString(", ")} "
+          s"Warning: Only java properties are supported in .scala-jvmopts file. Other options are ignored: ${otherOpts.mkString(", ")}"
         )
     // load java properties from config
     for {
@@ -201,14 +201,21 @@ object ScalaCli {
     // 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
-        }
-      }
+    val ignoredJavaOpts =
+      javaOpts
+        .flatMap(_.split("\\s+"))
+        .flatMap { opt =>
+          opt.stripPrefix("-D").split("=", 2) match {
+            case Array(key, value) =>
+              System.setProperty(key, value)
+              None
+            case ignored => Some(ignored) // non-property opts are ignored here
+          }
+        }.flatten
+    if ignoredJavaOpts.nonEmpty then
+      System.err.println(
+        s"Warning: Only java properties are supported in JAVA_OPTS and JDK_JAVA_OPTIONS environment variables. Other options are ignored: ${ignoredJavaOpts.mkString(", ")}"
+      )
   }
 
   private def main0(args: Array[String]): Unit = {

modules/integration/src/test/scala/scala/cli/integration/RunTestDefinitions.scala

@@ -2192,4 +2192,44 @@ abstract class RunTestDefinitions
       expect(warningCount == 1)
     }
   }
+
+  test(s"warn about invalid values present in JAVA_OPTS") {
+    val expectedOutput = "Hello"
+    TestInputs(os.rel / "example.sc" -> s"println(\"$expectedOutput\")")
+      .fromRoot { root =>
+        val invalidOpt = "--invalid"
+        val validOpt   = "-Dfoo=bar"
+        val res = os.proc(TestUtil.cli, "run", "example.sc", "--server=false", extraOptions)
+          .call(cwd = root, env = Map("JAVA_OPTS" -> s"$invalidOpt $validOpt"), stderr = os.Pipe)
+        val errOutput = res.err.trim()
+        expect(errOutput.contains(
+          s"Only java properties are supported in JAVA_OPTS"
+        ))
+        expect(errOutput.contains(s"Other options are ignored: $invalidOpt"))
+        expect(!errOutput.contains(validOpt))
+        expect(res.out.trim() == expectedOutput)
+      }
+  }
+
+  test(s"warn about invalid values present in .scala-jvmopts") {
+    val expectedOutput = "Hello"
+    val invalidOpt     = "--invalid"
+    val validOpt       = "-Dfoo=bar"
+    TestInputs(
+      os.rel / "example.sc" -> s"println(\"$expectedOutput\")",
+      os.rel / ".scala-jvmopts" ->
+        s"""$invalidOpt
+           |$validOpt
+           |""".stripMargin
+    )
+      .fromRoot { root =>
+        val res = os.proc(TestUtil.cli, "run", "example.sc", extraOptions)
+          .call(cwd = root, stderr = os.Pipe)
+        val errOutput = res.err.trim()
+        expect(errOutput.contains(s"Only java properties are supported in .scala-jvmopts file"))
+        expect(errOutput.contains(s"Other options are ignored: $invalidOpt"))
+        expect(!errOutput.contains(validOpt))
+        expect(res.out.trim() == expectedOutput)
+      }
+  }
 }