Use correct platform classloader on script evaluation in cli compiler

#KT-28475 fixed
also minor testing infrastruct refactoring

plugins/scripting/scripting-compiler/src/org/jetbrains/kotlin/scripting/compiler/plugin/JvmCliScriptEvaluationExtension.kt

@@ -23,7 +23,7 @@ class JvmCliScriptEvaluationExtension : AbstractScriptEvaluationExtension() {
 
     override fun ScriptEvaluationConfiguration.Builder.platformEvaluationConfiguration() {
         jvm {
-            baseClassLoader(null)
+            baseClassLoader(getPlatformClassLoader())
         }
     }
 
@@ -50,3 +50,9 @@ class JvmCliScriptEvaluationExtension : AbstractScriptEvaluationExtension() {
         arguments is K2JVMCompilerArguments && (arguments.script || arguments.expression != null)
 }
 
+private fun getPlatformClassLoader(): ClassLoader? =
+    try {
+        ClassLoader::class.java.getDeclaredMethod("getPlatformClassLoader")?.invoke(null)?.let { it as? ClassLoader }
+    } catch (_: Exception) {
+        null
+    }

plugins/scripting/scripting-compiler/tests/org/jetbrains/kotlin/scripting/compiler/plugin/ScriptingWithCliCompilerTest.kt

@@ -71,6 +71,19 @@ class ScriptingWithCliCompilerTest {
         )
     }
 
+    @Test
+    fun testJdkModules() {
+        // actually tests anything on JDKs 9+, on pre-9 it always works because JDK is not modularized anyway
+        runWithKotlinc(
+            arrayOf(
+                "-Xadd-modules=java.sql",
+                "-expression",
+                "println(javax.sql.DataSource::class.java)"
+            ),
+            listOf("interface javax.sql.DataSource")
+        )
+    }
+
     private fun getMainKtsClassPath(): List<File> {
         return listOf(
             File("dist/kotlinc/lib/kotlin-main-kts.jar").also {

plugins/scripting/scripting-compiler/tests/org/jetbrains/kotlin/scripting/compiler/plugin/testUtil.kt

@@ -26,6 +26,20 @@ fun runWithKotlinc(
     workDirectory: File? = null,
     classpath: List<File> = emptyList(),
     additionalEnvVars: Iterable<Pair<String, String>>? = null
+) {
+    runWithKotlinc(
+        arrayOf("-script", scriptPath),
+        expectedOutPatterns, expectedExitCode, workDirectory, classpath, additionalEnvVars
+    )
+}
+
+fun runWithKotlinc(
+    compilerArgs: Array<String>,
+    expectedOutPatterns: List<String> = emptyList(),
+    expectedExitCode: Int = 0,
+    workDirectory: File? = null,
+    classpath: List<File> = emptyList(),
+    additionalEnvVars: Iterable<Pair<String, String>>? = null
 ) {
     val executableName = "kotlinc"
     // TODO:
@@ -39,8 +53,7 @@ fun runWithKotlinc(
             add("-cp")
             add(classpath.joinToString(File.pathSeparator))
         }
-        add("-script")
-        add(scriptPath)
+        addAll(compilerArgs)
     }
     val processBuilder = ProcessBuilder(args)
     if (workDirectory != null) {