app/rust_builder/cargokit/gradle/plugin.gradle

/// This is copied from Cargokit (which is the official way to use it currently)
/// Details: https://fzyzcjy.github.io/flutter_rust_bridge/manual/integrate/builtin

import java.nio.file.Paths
import org.apache.tools.ant.taskdefs.condition.Os

CargoKitPlugin.file = buildscript.sourceFile

apply plugin: CargoKitPlugin

class CargoKitExtension {
    String manifestDir; // Relative path to folder containing Cargo.toml
    String libname; // Library name within Cargo.toml. Must be a cdylib
}

abstract class CargoKitBuildTask extends DefaultTask {

    @Input
    String buildMode

    @Input
    String buildDir

    @Input
    String outputDir

    @Input
    String ndkVersion

    @Input
    String sdkDirectory

    @Input
    int compileSdkVersion;

    @Input
    int minSdkVersion;

    @Input
    String pluginFile

    @Input
    List<String> targetPlatforms

    @TaskAction
    def build() {
        if (project.cargokit.manifestDir == null) {
            throw new GradleException("Property 'manifestDir' must be set on cargokit extension");
        }

        if (project.cargokit.libname == null) {
            throw new GradleException("Property 'libname' must be set on cargokit extension");
        }

        def executableName = Os.isFamily(Os.FAMILY_WINDOWS) ? "run_build_tool.cmd" : "run_build_tool.sh"
        def path = Paths.get(new File(pluginFile).parent, "..", executableName);

        def manifestDir = Paths.get(project.buildscript.sourceFile.parent, project.cargokit.manifestDir)

        def rootProjectDir = project.rootProject.projectDir

        project.exec {
            executable path
            args "build-gradle"
            environment "CARGOKIT_ROOT_PROJECT_DIR", rootProjectDir
            environment "CARGOKIT_TOOL_TEMP_DIR", "${buildDir}/build_tool"
            environment "CARGOKIT_MANIFEST_DIR", manifestDir
            environment "CARGOKIT_CONFIGURATION", buildMode
            environment "CARGOKIT_TARGET_TEMP_DIR", buildDir
            environment "CARGOKIT_OUTPUT_DIR", outputDir
            environment "CARGOKIT_NDK_VERSION", ndkVersion
            environment "CARGOKIT_SDK_DIR", sdkDirectory
            environment "CARGOKIT_COMPILE_SDK_VERSION", compileSdkVersion
            environment "CARGOKIT_MIN_SDK_VERSION", minSdkVersion
            environment "CARGOKIT_TARGET_PLATFORMS", targetPlatforms.join(",")
            environment "CARGOKIT_JAVA_HOME", System.properties['java.home']
        }
    }
}

class CargoKitPlugin implements Plugin<Project> {

    static String file;

    private Plugin findFlutterPlugin(Project rootProject) {
        _findFlutterPlugin(rootProject.childProjects)
    }

   private Plugin _findFlutterPlugin(Map projects) {
        for (project in projects) {
            for (plugin in project.value.getPlugins()) {
                if (plugin.class.name == "FlutterPlugin") {
                    return plugin;
                }
            }
            def plugin = _findFlutterPlugin(project.value.childProjects);
            if (plugin != null) {
                return plugin;
            }
        }
        return null;
    }

    @Override
    void apply(Project project) {
        def plugin = findFlutterPlugin(project.rootProject);

        project.extensions.create("cargokit", CargoKitExtension)

        if (plugin == null) {
            print("Flutter plugin not found, CargoKit plugin will not be applied.")
            return;
        }

        def cargoBuildDir = "${project.buildDir}/build"

        plugin.project.android.applicationVariants.all { variant ->

            final buildType = variant.buildType.name

            def cargoOutputDir = "${project.buildDir}/jniLibs/${buildType}";
            def jniLibs = project.android.sourceSets.maybeCreate(buildType).jniLibs;
            jniLibs.srcDir(new File(cargoOutputDir))

            def platforms = plugin.getTargetPlatforms().collect()

            // Same thing addFlutterDependencies does in flutter.gradle
            if (buildType == "debug") {
                platforms.add("android-x86")
                platforms.add("android-x64")
            }

            // The task name depends on plugin properties, which are not available
            // at this point
            project.getGradle().afterProject {
                def taskName = "cargokitCargoBuild${project.cargokit.libname.capitalize()}${buildType.capitalize()}";

                if (project.tasks.findByName(taskName)) {
                    return
                }

                if (plugin.project.android.ndkVersion == null) {
                    throw new GradleException("Please set 'android.ndkVersion' in 'app/build.gradle'.")
                }

                def task = project.tasks.create(taskName, CargoKitBuildTask.class) {
                    buildMode = variant.buildType.name
                    buildDir = cargoBuildDir
                    outputDir = cargoOutputDir
                    ndkVersion = plugin.project.android.ndkVersion
                    sdkDirectory = plugin.project.android.sdkDirectory
                    minSdkVersion = plugin.project.android.defaultConfig.minSdkVersion.apiLevel as int
                    compileSdkVersion = plugin.project.android.compileSdkVersion.substring(8) as int
                    targetPlatforms = platforms
                    pluginFile = CargoKitPlugin.file
                }
                def onTask = { newTask ->
                    if (newTask.name == "merge${buildType.capitalize()}NativeLibs") {
                        newTask.dependsOn task
                        // Fix gradle 7.4.2 not picking up JNI library changes
                        newTask.outputs.upToDateWhen { false }
                    }
                }
                project.tasks.each onTask
                project.tasks.whenTaskAdded onTask
            }
        }
    }
}