Upgrade to Kotlin 1.4 RC

- The compiler is configured to retain compatibility with Kotlin 1.3.
- Explicit API mode is not yet enabled but could be in the future.
- Some exceptions thrown by Kotlin have changed to NullPointerException,
  see https://youtrack.jetbrains.com/issue/KT-22275 for more details.

Closes gh-24171

build.gradle

@@ -1,6 +1,6 @@
 plugins {
 	id 'io.spring.dependency-management' version '1.0.9.RELEASE' apply false
-	id 'org.jetbrains.kotlin.jvm' version '1.3.72' apply false
+	id 'org.jetbrains.kotlin.jvm' version '1.4.0-rc' apply false
 	id 'org.jetbrains.dokka' version '0.10.1' apply false
 	id 'org.asciidoctor.jvm.convert' version '2.4.0'
 	id 'io.spring.nohttp' version '0.0.5.RELEASE'
@@ -29,8 +29,8 @@ configure(allprojects) { project ->
 			mavenBom "io.r2dbc:r2dbc-bom:Arabba-SR5"
 			mavenBom "io.rsocket:rsocket-bom:1.1.0-SNAPSHOT"
 			mavenBom "org.eclipse.jetty:jetty-bom:9.4.30.v20200611"
-			mavenBom "org.jetbrains.kotlin:kotlin-bom:1.3.72"
-			mavenBom "org.jetbrains.kotlinx:kotlinx-coroutines-bom:1.3.7"
+			mavenBom "org.jetbrains.kotlin:kotlin-bom:1.4.0-rc"
+			mavenBom "org.jetbrains.kotlinx:kotlinx-coroutines-bom:1.3.8-1.4.0-rc"
 			mavenBom "org.junit:junit-bom:5.6.2"
 		}
 		dependencies {
@@ -311,6 +311,8 @@ configure([rootProject] + javaProjects) { project ->
 		compileKotlin {
 			kotlinOptions {
 				jvmTarget = "1.8"
+				languageVersion = "1.3"
+				apiVersion = "1.3"
 				freeCompilerArgs = ["-Xjsr305=strict"]
 				allWarningsAsErrors = true
 			}

spring-jdbc/src/test/kotlin/org/springframework/jdbc/core/JdbcOperationsExtensionsTests.kt

@@ -53,7 +53,7 @@ class JdbcOperationsExtensionsTests {
 	@Test  // gh-22682
 	fun `queryForObject with nullable RowMapper-like function`() {
 		every { template.queryForObject(sql, any<RowMapper<Int>>(), 3) } returns null
-		assertThat(template.queryForObject(sql, 3) { _, _ -> null as Int? }).isNull()
+		assertThat(template.queryForObject<Int?>(sql, 3) { _, _ -> null }).isNull()
 		verify { template.queryForObject(eq(sql), any<RowMapper<Int?>>(), eq(3)) }
 	}
 
@@ -130,7 +130,7 @@ class JdbcOperationsExtensionsTests {
 
 	@Test
 	fun `query with RowMapper-like function`() {
-		val list = listOf(1, 2, 3)
+		val list = mutableListOf(1, 2, 3)
 		every { template.query(sql, ofType<RowMapper<*>>(), 3) } returns list
 		assertThat(template.query(sql, 3) { rs, _ ->
 			rs.getInt(1)

spring-messaging/src/test/kotlin/org/springframework/messaging/simp/annotation/support/SimpAnnotationMethodMessageHandlerKotlinTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -132,7 +132,7 @@ class SimpAnnotationMethodMessageHandlerKotlinTests {
         messageHandler.registerHandler(testController)
         messageHandler.handleMessage(message)
         assertThat(testController.exception).isNotNull()
-		assertThat(testController.exception).isInstanceOf(IllegalArgumentException::class.java)
+		assertThat(testController.exception).isInstanceOf(NullPointerException::class.java)
     }
 
     private fun createMessage(destination: String, headers: Map<String, String?>): Message<ByteArray> {

spring-web/src/test/kotlin/org/springframework/web/method/annotation/RequestParamMethodArgumentResolverKotlinTests.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2020 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,7 +16,6 @@
 
 package org.springframework.web.method.annotation
 
-import org.assertj.core.api.Assertions
 import org.assertj.core.api.Assertions.assertThat
 import org.assertj.core.api.Assertions.assertThatExceptionOfType
 import org.junit.jupiter.api.BeforeEach
@@ -139,7 +138,7 @@ class RequestParamMethodArgumentResolverKotlinTests {
 
 	@Test
 	fun resolveNonNullableNotRequiredWithoutParameter() {
-		assertThatExceptionOfType(TypeCastException::class.java).isThrownBy {
+		assertThatExceptionOfType(NullPointerException::class.java).isThrownBy {
 			resolver.resolveArgument(nonNullableParamNotRequired, null, webRequest, binderFactory) as String
 		}
 	}
@@ -221,7 +220,7 @@ class RequestParamMethodArgumentResolverKotlinTests {
 		request.method = HttpMethod.POST.name
 		request.contentType = MediaType.MULTIPART_FORM_DATA_VALUE
 
-		assertThatExceptionOfType(TypeCastException::class.java).isThrownBy {
+		assertThatExceptionOfType(NullPointerException::class.java).isThrownBy {
 			resolver.resolveArgument(nonNullableMultipartParamNotRequired, null, webRequest, binderFactory) as MultipartFile
 		}
 	}

spring-webflux/spring-webflux.gradle

@@ -47,8 +47,7 @@ dependencies {
 	testCompile('org.apache.httpcomponents.client5:httpclient5:5.0')
 	testCompile('org.apache.httpcomponents.core5:httpcore5-reactive:5.0')
 	testCompile("com.squareup.okhttp3:mockwebserver")
-	testCompile("org.jetbrains.kotlin:kotlin-script-runtime")
-	testRuntime("org.jetbrains.kotlin:kotlin-scripting-jsr223-embeddable")
+	testRuntime("org.jetbrains.kotlin:kotlin-scripting-jsr223")
 	testRuntime("org.jruby:jruby")
 	testRuntime("org.python:jython-standalone")
 	testRuntime("org.synchronoss.cloud:nio-multipart-parser")

spring-webmvc/spring-webmvc.gradle

@@ -60,8 +60,8 @@ dependencies {
 	testCompile("javax.validation:validation-api")
 	testCompile("io.projectreactor:reactor-core")
 	testCompile("io.reactivex.rxjava3:rxjava")
-	testCompile("org.jetbrains.kotlin:kotlin-script-runtime")
-	testRuntime("org.jetbrains.kotlin:kotlin-scripting-jsr223-embeddable")
+	testRuntime("org.jetbrains.kotlin:kotlin-scripting-jsr223")
+	testRuntime("org.jetbrains.kotlinx:kotlinx-coroutines-core") // Temporary dependency to fix a NoClassDefFoundError error, should not be necessary
 	testRuntime("org.jruby:jruby")
 	testRuntime("org.python:jython-standalone")
 	testRuntime("org.webjars:underscorejs")