Reverts "Convert the Flutter Gradle Plugin entirely to Kotlin source (flutter#166114)" (flutter#166666)

<!-- start_original_pr_link -->
Reverts: flutter#166114
<!-- end_original_pr_link -->
<!-- start_initiating_author -->
Initiated by: gmackall
<!-- end_initiating_author -->
<!-- start_revert_reason -->
Reason for reverting: a failing postsubmit
<!-- end_revert_reason -->
<!-- start_original_pr_author -->
Original PR Author: gmackall
<!-- end_original_pr_author -->

<!-- start_reviewers -->
Reviewed By: {bartekpacia, reidbaker}
<!-- end_reviewers -->

<!-- start_revert_body -->
This change reverts the following previous change:
Finishes the conversion of the Flutter Gradle plugin from Groovy to
Kotlin.

Fixes flutter#121541.
Fixes flutter#166287.

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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[Tree Hygiene]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md
[test-exempt]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
[Features we expect every widget to implement]:
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[CLA]: https://cla.developers.google.com/
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[breaking change policy]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes
[Discord]:
https://github.com/flutter/flutter/blob/main/docs/contributing/Chat.md
[Data Driven Fixes]:
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<!-- end_revert_body -->

Co-authored-by: auto-submit[bot] <[email protected]>

Author: auto-submit[bot]

packages/flutter_tools/gradle/build.gradle.kts

@@ -34,7 +34,7 @@ gradlePlugin {
         // The "flutterPlugin" name isn't used anywhere.
         create("flutterPlugin") {
             id = "dev.flutter.flutter-gradle-plugin"
-            implementationClass = "com.flutter.gradle.FlutterPlugin"
+            implementationClass = "FlutterPlugin"
         }
         // The "flutterAppPluginLoaderPlugin" name isn't used anywhere.
         create("flutterAppPluginLoaderPlugin") {

packages/flutter_tools/gradle/src/main/scripts/CMakeLists.txt renamed to packages/flutter_tools/gradle/src/main/groovy/CMakeLists.txt

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-package com.flutter.gradle.tasks
+package com.flutter.gradle
 
 import org.gradle.api.DefaultTask
 import org.gradle.api.tasks.Input

packages/flutter_tools/gradle/src/main/groovy/flutter.groovy

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-package com.flutter.gradle.tasks
+package com.flutter.gradle
 
 import androidx.annotation.VisibleForTesting
 import org.gradle.api.Action

packages/flutter_tools/gradle/src/main/kotlin/tasks/BaseFlutterTask.kt renamed to packages/flutter_tools/gradle/src/main/kotlin/BaseFlutterTask.kt

@@ -25,6 +25,7 @@ object FlutterPluginConstants {
     const val INTERMEDIATES_DIR = "intermediates"
     const val FLUTTER_STORAGE_BASE_URL = "FLUTTER_STORAGE_BASE_URL"
     const val DEFAULT_MAVEN_HOST = "https://storage.googleapis.com"
+    const val WEBSITE_DEPLOYMENT_ANDROID_BUILD_CONFIG = "https://flutter.dev/to/review-gradle-config"
 
     /** Maps platforms to ABI architectures. */
     @JvmStatic val PLATFORM_ARCH_MAP =
@@ -41,7 +42,7 @@ object FlutterPluginConstants {
      * Otherwise, the Play Store will complain that the APK variants have the same version.
      */
     @JvmStatic val ABI_VERSION =
-        mapOf<String, Int>(
+        mapOf<String, Int>( // Explicit type for clarity, though inferred
             ARCH_ARM32 to 1,
             ARCH_ARM64 to 2,
             ARCH_X86 to 3,

packages/flutter_tools/gradle/src/main/kotlin/tasks/BaseFlutterTaskHelper.kt renamed to packages/flutter_tools/gradle/src/main/kotlin/BaseFlutterTaskHelper.kt

@@ -10,7 +10,6 @@ import com.android.build.gradle.api.ApplicationVariant
 import com.android.build.gradle.api.BaseVariantOutput
 import com.android.build.gradle.tasks.ProcessAndroidResources
 import com.android.builder.model.BuildType
-import com.flutter.gradle.plugins.PluginHandler
 import groovy.lang.Closure
 import groovy.util.Node
 import groovy.util.XmlParser
@@ -140,6 +139,19 @@ object FlutterPluginUtils {
 
     // TODO(54566): Can remove this function and its call sites once resolved.
 
+    /**
+     * Returns `true` if the given project is a plugin project having an `android` directory
+     * containing a `build.gradle` or `build.gradle.kts` file.
+     */
+    @JvmStatic
+    @JvmName("pluginSupportsAndroidPlatform")
+    internal fun pluginSupportsAndroidPlatform(project: Project): Boolean {
+        val buildGradle = File(File(project.projectDir.parentFile, "android"), "build.gradle")
+        val buildGradleKts =
+            File(File(project.projectDir.parentFile, "android"), "build.gradle.kts")
+        return buildGradle.exists() || buildGradleKts.exists()
+    }
+
     /**
      * Returns the Gradle settings script for the build. When both Groovy and
      * Kotlin variants exist, then Groovy (settings.gradle) is preferred over
@@ -394,7 +406,7 @@ object FlutterPluginUtils {
         return project.property(PROP_LOCAL_ENGINE_BUILD_MODE) == flutterBuildMode
     }
 
-    internal fun getAndroidExtension(project: Project): BaseExtension {
+    private fun getAndroidExtension(project: Project): BaseExtension {
         // Common supertype of the android extension types.
         // But maybe this should be https://developer.android.com/reference/tools/gradle-api/8.7/com/android/build/api/dsl/TestedExtension.
         return project.extensions.findByType(BaseExtension::class.java)!!
@@ -599,7 +611,7 @@ object FlutterPluginUtils {
 
         // Otherwise, point to an empty CMakeLists.txt, and ignore associated warnings.
         gradleProjectAndroidExtension.externalNativeBuild.cmake.path(
-            "$flutterSdkRootPath/packages/flutter_tools/gradle/src/main/scripts/CMakeLists.txt"
+            "$flutterSdkRootPath/packages/flutter_tools/gradle/src/main/groovy/CMakeLists.txt"
         )
 
         // AGP defaults to outputting build artifacts in `android/app/.cxx`. This directory is a
@@ -644,7 +656,7 @@ object FlutterPluginUtils {
     internal fun addFlutterDependencies(
         project: Project,
         buildType: BuildType,
-        pluginHandler: PluginHandler,
+        pluginList: List<Map<String?, Any?>>,
         engineVersion: String
     ) {
         val flutterBuildMode: String = buildModeFor(buildType)
@@ -664,9 +676,11 @@ object FlutterPluginUtils {
         // embedding.
         val pluginsThatIncludeFlutterEmbeddingAsTransitiveDependency: List<Map<String?, Any?>> =
             if (flutterBuildMode == "release") {
-                pluginHandler.getPluginListWithoutDevDependencies()
+                getPluginListWithoutDevDependencies(
+                    pluginList
+                )
             } else {
-                pluginHandler.getPluginList()
+                pluginList
             }
 
         if (!isFlutterAppProject(project) || pluginsThatIncludeFlutterEmbeddingAsTransitiveDependency.isEmpty()) {
@@ -688,6 +702,143 @@ object FlutterPluginUtils {
         }
     }
 
+    /**
+     * Gets the list of plugins (as map) that support the Android platform and are dependencies of the
+     * Android project excluding dev dependencies.
+     *
+     * The map value contains either the plugins `name` (String),
+     * its `path` (String), or its `dependencies` (List<String>).
+     * See [NativePluginLoader#getPlugins] in packages/flutter_tools/gradle/src/main/scripts/native_plugin_loader.gradle.kts
+     */
+    private fun getPluginListWithoutDevDependencies(pluginList: List<Map<String?, Any?>>): List<Map<String?, Any?>> =
+        pluginList.filter { pluginObject -> pluginObject["dev_dependency"] == false }
+
+    /**
+     * Add the dependencies on other plugin projects to the plugin project.
+     * A plugin A can depend on plugin B. As a result, this dependency must be surfaced by
+     * making the Gradle plugin project A depend on the Gradle plugin project B.
+     */
+    @JvmStatic
+    @JvmName("configurePluginDependencies")
+    internal fun configurePluginDependencies(
+        project: Project,
+        pluginObject: Map<String?, Any?>
+    ) {
+        val pluginName: String =
+            requireNotNull(pluginObject["name"] as? String) {
+                "Missing valid \"name\" property for plugin object: $pluginObject"
+            }
+        val pluginProject: Project = project.rootProject.findProject(":$pluginName") ?: return
+
+        getAndroidExtension(project).buildTypes.forEach { buildType ->
+            val flutterBuildMode: String = buildModeFor(buildType)
+            if (flutterBuildMode == "release" && (pluginObject["dev_dependency"] as? Boolean == true)) {
+                // This plugin is a dev dependency will not be included in the
+                // release build, so no need to add its dependencies.
+                return@forEach
+            }
+            val dependencies = requireNotNull(pluginObject["dependencies"] as? List<*>)
+            dependencies.forEach innerForEach@{ pluginDependencyName ->
+                check(pluginDependencyName is String)
+                if (pluginDependencyName.isEmpty()) {
+                    return@innerForEach
+                }
+
+                val dependencyProject =
+                    project.rootProject.findProject(":$pluginDependencyName") ?: return@innerForEach
+                pluginProject.afterEvaluate {
+                    pluginProject.dependencies.add("implementation", dependencyProject)
+                }
+            }
+        }
+    }
+
+    /**
+     * Performs configuration related to the plugin's Gradle [Project], including
+     * 1. Adding the plugin itself as a dependency to the main project.
+     * 2. Adding the main project's build types to the plugin's build types.
+     * 3. Adding a dependency on the Flutter embedding to the plugin.
+     *
+     * Should only be called on plugins that support the Android platform.
+     */
+    @JvmStatic
+    @JvmName("configurePluginProject")
+    internal fun configurePluginProject(
+        project: Project,
+        pluginObject: Map<String?, Any?>,
+        engineVersion: String
+    ) {
+        // TODO(gmackall): should guard this with a pluginObject.contains().
+        val pluginName =
+            requireNotNull(pluginObject["name"] as? String) { "Plugin name must be a string for plugin object: $pluginObject" }
+        val pluginProject: Project = project.rootProject.findProject(":$pluginName") ?: return
+
+        // Apply the "flutter" Gradle extension to plugins so that they can use it's vended
+        // compile/target/min sdk values.
+        pluginProject.extensions.create("flutter", FlutterExtension::class.java)
+
+        // Add plugin dependency to the app project. We only want to add dependency
+        // for dev dependencies in non-release builds.
+        project.afterEvaluate {
+            getAndroidExtension(project).buildTypes.forEach { buildType ->
+                if (!(pluginObject["dev_dependency"] as Boolean) || buildType.name != "release") {
+                    project.dependencies.add("${buildType.name}Api", pluginProject)
+                }
+            }
+        }
+
+        // Wait until the Android plugin loaded.
+        pluginProject.afterEvaluate {
+            // Checks if there is a mismatch between the plugin compileSdkVersion and the project compileSdkVersion.
+            val projectCompileSdkVersion: String = getCompileSdkFromProject(project)
+            val pluginCompileSdkVersion: String = getCompileSdkFromProject(pluginProject)
+            // TODO(gmackall): This is doing a string comparison, which is odd and also can be wrong
+            //                 when comparing preview versions (against non preview, and also in the
+            //                 case of alphabet reset which happened with "Baklava".
+            if (pluginCompileSdkVersion > projectCompileSdkVersion) {
+                project.logger.quiet("Warning: The plugin $pluginName requires Android SDK version $pluginCompileSdkVersion or higher.")
+                project.logger.quiet(
+                    "For more information about build configuration, see ${FlutterPluginConstants.WEBSITE_DEPLOYMENT_ANDROID_BUILD_CONFIG}."
+                )
+            }
+
+            getAndroidExtension(project).buildTypes.forEach { buildType ->
+                addEmbeddingDependencyToPlugin(project, pluginProject, buildType, engineVersion)
+            }
+        }
+    }
+
+    private fun addEmbeddingDependencyToPlugin(
+        project: Project,
+        pluginProject: Project,
+        buildType: BuildType,
+        engineVersion: String
+    ) {
+        val flutterBuildMode: String = buildModeFor(buildType)
+        // TODO(gmackall): this should be safe to remove, as the minimum required AGP is well above
+        //                 3.5. We should try to remove it.
+        // In AGP 3.5, the embedding must be added as an API implementation,
+        // so java8 features are desugared against the runtime classpath.
+        // For more, see https://github.com/flutter/flutter/issues/40126
+        if (!supportsBuildMode(pluginProject, flutterBuildMode)) {
+            return
+        }
+        if (!pluginProject.hasProperty("android")) {
+            return
+        }
+
+        // Copy build types from the app to the plugin.
+        // This allows to build apps with plugins and custom build types or flavors.
+        getAndroidExtension(pluginProject).buildTypes.addAll(getAndroidExtension(project).buildTypes)
+
+        // The embedding is API dependency of the plugin, so the AGP is able to desugar
+        // default method implementations when the interface is implemented by a plugin.
+        //
+        // See https://issuetracker.google.com/139821726, and
+        // https://github.com/flutter/flutter/issues/72185 for more details.
+        addApiDependencies(pluginProject, buildType.name, "io.flutter:flutter_embedding_$flutterBuildMode:$engineVersion")
+    }
+
     // ------------------ Task adders (a subset of the above category)
 
     // Add a task that can be called on flutter projects that prints the Java version used in Gradle.

packages/flutter_tools/gradle/src/main/kotlin/FlutterPlugin.kt

@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-package com.flutter.gradle.tasks
+package com.flutter.gradle
 
 import org.gradle.api.file.CopySpec
 import org.gradle.api.file.FileCollection

packages/flutter_tools/gradle/src/main/kotlin/FlutterPluginConstants.kt

@@ -2,9 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-package com.flutter.gradle.tasks
+package com.flutter.gradle
 
-import com.flutter.gradle.FlutterPluginConstants
 import org.gradle.api.Project
 import org.gradle.api.file.CopySpec
 import org.gradle.api.file.FileCollection