fix(android): skip explicit Kotlin plugin when AGP registers the kotlin extension (#1453)

Co-authored-by: Daniel Williams <me@dannyhw.com>

Author: gabrieldonadel

.changeset/agp9-builtin-kotlin.md

@@ -0,0 +1,9 @@
+---
+"@callstack/repack": patch
+---
+
+Fix Android configuration on AGP 9, where built-in Kotlin support registers the
+`kotlin` extension itself and the explicit `kotlin-android` apply failed with
+"Cannot add extension with name 'kotlin'". The plugin - and the `kotlinOptions`
+block it contributes - is now applied only when nothing has registered that
+extension, leaving AGP 8 and `android.builtInKotlin=false` projects unchanged.

packages/repack/android/build.gradle

@@ -31,7 +31,14 @@ def isNewArchitectureEnabled() {
 }
 
 apply plugin: 'com.android.library'
-apply plugin: 'kotlin-android'
+// AGP 9 ships built-in Kotlin support and registers the `kotlin` extension
+// itself. Applying the Kotlin plugin on top of it fails configuration with
+// "Cannot add extension with name 'kotlin'". Only apply it when nothing has
+// registered that extension yet.
+def appliesKotlinPlugin = project.extensions.findByName('kotlin') == null
+if (appliesKotlinPlugin) {
+    apply plugin: 'kotlin-android'
+}
 
 if (isNewArchitectureEnabled()) {
     apply plugin: "com.facebook.react"
@@ -130,11 +137,13 @@ android {
         }
     }
 
-    kotlinOptions {
-        if (REACT_NATIVE_MINOR_VERSION < 69) {
-            jvmTarget = JavaVersion.VERSION_1_8
-        } else if (REACT_NATIVE_MINOR_VERSION < 73) {
-            jvmTarget = JavaVersion.VERSION_11
+    if (appliesKotlinPlugin) {
+        kotlinOptions {
+            if (REACT_NATIVE_MINOR_VERSION < 69) {
+                jvmTarget = JavaVersion.VERSION_1_8
+            } else if (REACT_NATIVE_MINOR_VERSION < 73) {
+                jvmTarget = JavaVersion.VERSION_11
+            }
         }
     }