Set apiVersion and languageVersion to 2.0 to ensure backwards compatibility

Author: Hugo Costa

build.gradle.kts

@@ -189,6 +189,8 @@ subprojects {
   tasks.withType<KotlinCompile> {
     compilerOptions {
       jvmTarget.set(projectJvmTarget)
+      apiVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0)
+      languageVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0)
       freeCompilerArgs = listOf(
         "-Xjvm-default=all",
       )

okhttp/api/jvm/okhttp.api

@@ -1240,7 +1240,7 @@ public abstract interface class okhttp3/TrailersSource {
 	public static final field Companion Lokhttp3/TrailersSource$Companion;
 	public static final field EMPTY Lokhttp3/TrailersSource;
 	public abstract fun get ()Lokhttp3/Headers;
-	public fun peek ()Lokhttp3/Headers;
+	public abstract fun peek ()Lokhttp3/Headers;
 }
 
 public final class okhttp3/TrailersSource$Companion {

okhttp/build.gradle.kts

@@ -50,6 +50,11 @@ val generateIdnaMappingTable = tasks.register<JavaExec>("generateIdnaMappingTabl
 kotlin {
   jvmToolchain(8)
 
+  compilerOptions {
+    apiVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0)
+    languageVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0)
+  }
+
   jvm {
   }
 
@@ -284,6 +289,8 @@ afterEvaluate {
 // but it's easy enough for us to keep it working. https://github.com/square/okhttp/issues/8826
 tasks.withType<KotlinCompile> {
   compilerOptions {
+    apiVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0)
+    languageVersion.set(org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0)
     freeCompilerArgs = listOf("-module-name=okhttp")
   }
 }