Fix binary incompatibility with Android Gradle plugin 3.2.0-alpha06

Remove a non-reflective usage of the ResourceSet class, which has been
moved to a different package between versions. Access it through
reflection instead. This is a workaround. We can introduce a proper
fix once we have a public API in the Android plugin.

The test case that could detect the compatibility issue is
`testAndroidExtensionsManyVariants` (it uses experimental Android
extensions), but we did not run it with 3.2.0-alpha6. This commit
adds a test class with the same tests for 3.2.0-alpha6.

Issue #KT-23192 Fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/AbstractKotlinAndroidGradleTests.kt

@@ -13,7 +13,15 @@ import java.io.File
 class KotlinAndroidGradleIT : AbstractKotlinAndroidGradleTests(gradleVersion = GradleVersionRequired.AtLeast("3.4"), androidGradlePluginVersion = "2.3.0")
 class KotlinAndroidWithJackGradleIT : AbstractKotlinAndroidWithJackGradleTests(androidGradlePluginVersion = "2.3.+")
 
-class KotlinAndroid30GradleIT : AbstractKotlinAndroidGradleTests(gradleVersion = GradleVersionRequired.AtLeast("4.1"), androidGradlePluginVersion = "3.0.0-beta1") {
+// TODO If we there is a way to fetch the latest Android plugin version, test against the latest version
+class KotlinAndroid32GradleIT : KotlinAndroid3GradleIT(GradleVersionRequired.AtLeast("4.5"), "3.2.0-alpha06")
+
+class KotlinAndroid30GradleIT : KotlinAndroid3GradleIT(GradleVersionRequired.AtLeast("4.1"), "3.0.0")
+
+abstract class KotlinAndroid3GradleIT(
+    gradleVersionRequired: GradleVersionRequired,
+    androidGradlePluginVersion: String
+) : AbstractKotlinAndroidGradleTests(gradleVersionRequired, androidGradlePluginVersion) {
 
     @Test
     fun testApplyWithFeaturePlugin() {
@@ -314,5 +322,4 @@ abstract class AbstractKotlinAndroidWithJackGradleTests(
             assertContains("Kotlin Gradle plugin does not support the deprecated Jack toolchain")
         }
     }
-}
-
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/AndroidProject/build.gradle

@@ -13,7 +13,7 @@ buildscript {
 allprojects {
     repositories {
         mavenLocal()
-        mavenCentral()
+        jcenter()
         maven { url 'https://maven.google.com' }
     }
 }

libraries/tools/kotlin-gradle-plugin/src/agp25/kotlin/org/jetbrains/kotlin/gradle/plugin/android/Android25ProjectHandler.kt

@@ -4,7 +4,6 @@ import com.android.build.gradle.*
 import com.android.build.gradle.api.*
 import com.android.build.gradle.tasks.MergeResources
 import com.android.builder.model.SourceProvider
-import com.android.ide.common.res2.ResourceSet
 import org.gradle.api.Project
 import org.gradle.api.file.FileCollection
 import org.gradle.api.tasks.compile.AbstractCompile
@@ -120,7 +119,7 @@ class Android25ProjectHandler(kotlinConfigurationTools: KotlinConfigurationTools
     }
 
     override fun getResDirectories(variantData: BaseVariant): List<File> {
-        return variantData.mergeResources?.computeResourceSetList0()?.flatMap { it.sourceFiles } ?: emptyList()
+        return variantData.mergeResources?.computeResourceSetList0() ?: emptyList()
     }
 
     private inner class KaptVariant(variantData: BaseVariant) : KaptVariantData<BaseVariant>(variantData) {
@@ -143,17 +142,26 @@ class Android25ProjectHandler(kotlinConfigurationTools: KotlinConfigurationTools
         }
     }
 
-    //TODO once the Android plugin reaches its 3.0.0 release, consider compiling against it (remove the reflective call)
-    //TODO this is a private API for now
-    private fun MergeResources.computeResourceSetList0(): List<ResourceSet>? {
+    //TODO A public API is expected for this purpose. Once it is available, use the public API
+    private fun MergeResources.computeResourceSetList0(): List<File>? {
         val computeResourceSetListMethod = MergeResources::class.java.declaredMethods
                 .firstOrNull { it.name == "computeResourceSetList" && it.parameterCount == 0 } ?: return null
 
         val oldIsAccessible = computeResourceSetListMethod.isAccessible
         try {
             computeResourceSetListMethod.isAccessible = true
-            @Suppress("UNCHECKED_CAST")
-            return computeResourceSetListMethod.invoke(this) as? List<ResourceSet>
+
+            val resourceSets = computeResourceSetListMethod.invoke(this) as? Iterable<*>
+
+            return resourceSets
+                ?.mapNotNull { resourceSet ->
+                    val getSourceFiles = resourceSet?.javaClass?.methods?.find { it.name == "getSourceFiles" && it.parameterCount == 0 }
+                    val files = getSourceFiles?.invoke(resourceSet)
+                    @Suppress("UNCHECKED_CAST")
+                    files as? Iterable<File>
+                }
+                ?.flatten()
+
         } finally {
             computeResourceSetListMethod.isAccessible = oldIsAccessible
         }