Use correct class loader to load .kotlin_builtins in reflection

#KT-30749 Fixed

compiler/testData/reflection/classLoaderForBuiltIns/Main.java

@@ -0,0 +1,15 @@
+import java.io.*;
+import java.net.*;
+
+public class Main {
+    public static void main(String[] args) throws Exception {
+        URL[] urls = new URL[args.length];
+        for (int i = 0; i < args.length; i++) {
+            urls[i] = new File(args[i]).toURI().toURL();
+        }
+
+        ClassLoader cl = new URLClassLoader(urls);
+        Class<?> c = cl.loadClass("TestKt");
+        c.getDeclaredMethods()[0].invoke(null);
+    }
+}

compiler/testData/reflection/classLoaderForBuiltIns/test.kt

@@ -0,0 +1,3 @@
+fun test() {
+    println(String::class.supertypes)
+}

compiler/tests/org/jetbrains/kotlin/reflection/ReflectionIntegrationTest.kt

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license
+ * that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.reflection
+
+import org.jetbrains.kotlin.codegen.forTestCompile.ForTestCompileRuntime
+import org.jetbrains.kotlin.test.CompilerTestUtil
+import org.jetbrains.kotlin.test.KotlinTestUtils
+import org.jetbrains.kotlin.test.testFramework.KtUsefulTestCase
+import java.io.File
+import java.util.concurrent.TimeUnit
+
+class ReflectionIntegrationTest : KtUsefulTestCase() {
+    // This test checks that we use the correct class loader to load .kotlin_builtins resource files.
+    // On Android, the class loader used to load the application classes differs from the boot class loader (which loads core JDK classes),
+    // so attempting to find kotlin/kotlin.kotlin_builtins in the same class loader that found java.lang.Object can fail.
+    // We should always use the class loader that loads stdlib class files to locate .kotlin_builtins resource files
+    fun testClassLoaderForBuiltIns() {
+        val tmpdir = KotlinTestUtils.tmpDirForTest(this)
+
+        val root = KotlinTestUtils.getTestDataPathBase() + "/reflection/classLoaderForBuiltIns"
+        KotlinTestUtils.compileJavaFiles(
+            listOf(File("$root/Main.java")),
+            listOf("-d", tmpdir.absolutePath)
+        )
+
+        val lib = CompilerTestUtil.compileJvmLibrary(File("$root/test.kt"))
+
+        val javaHome = System.getProperty("java.home")
+        val javaExe = File(javaHome, "bin/java.exe").takeIf(File::exists)
+            ?: File(javaHome, "bin/java").takeIf(File::exists)
+            ?: error("Can't find 'java' executable in $javaHome")
+
+        val command = arrayOf(
+            javaExe.absolutePath,
+            "-ea",
+            "-classpath",
+            tmpdir.absolutePath,
+            "Main",
+            lib.absolutePath,
+            ForTestCompileRuntime.runtimeJarForTests().absolutePath,
+            ForTestCompileRuntime.reflectJarForTests().absolutePath
+        )
+
+        val process = ProcessBuilder(*command).inheritIO().start()
+        process.waitFor(1, TimeUnit.MINUTES)
+        assertEquals(0, process.exitValue())
+    }
+}

core/descriptors.runtime/src/kotlin/reflect/jvm/internal/components/RuntimeModuleData.kt

@@ -87,8 +87,11 @@ class RuntimeModuleData private constructor(
                 binaryClassAnnotationAndConstantLoader, lazyJavaPackageFragmentProvider, notFoundClasses,
                 RuntimeErrorReporter, LookupTracker.DO_NOTHING, ContractDeserializer.DEFAULT
             )
+
+            // .kotlin_builtins files should be found by the same class loader that loaded stdlib classes
+            val stdlibClassLoader = Unit::class.java.classLoader
             val builtinsProvider = JvmBuiltInsPackageFragmentProvider(
-                storageManager, reflectKotlinClassFinder, module, notFoundClasses, builtIns.settings, builtIns.settings,
+                storageManager, ReflectKotlinClassFinder(stdlibClassLoader), module, notFoundClasses, builtIns.settings, builtIns.settings,
                 DeserializationConfiguration.Default
             )