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Grazel

Grazel stands for Gradle to Bazel. A Gradle plugin to migrate Android projects to Bazel build system in an incremental and automated fashion.

How it works

It works by automatically generating Bazel scripts for given Android project based on your Gradle configuration. For simple projects, it should be able to migrate, fully build and launch the app with bazel mobile-install //<target-name>.

For example, for the following Gradle configuration:

apply plugin: "com.android.library"
apply plugin: "kotlin-android"

android {
    compileSdkVersion rootProject.compileSdk
    defaultConfig {
        minSdkVersion rootProject.minSdk
        targetSdkVersion rootProject.targetSdk
        versionCode 1
        versionName "1.0"
    }
}

dependencies {
    implementation project(":app")
    implementation project(":base")
    implementation "androidx.test.espresso:espresso-idling-resource:3.2.0"
}

Grazel's migrateToBazel task generates the following Bazel build script:

load("@io_bazel_rules_kotlin//kotlin:kotlin.bzl", "kt_android_library")

kt_android_library(
    name = "quiz",
    srcs = glob([
        "src/main/java/**/*.kt",
    ]),
    custom_package = "com.google.samples.apps.topeka.quiz",
    manifest = "src/main/AndroidManifest.xml",
    resource_files = glob([
        "src/main/res/**",
    ]),
    visibility = [
        "//visibility:public",
    ],
    deps = [
        "//app",
        "//base",
        "@maven//:androidx_test_espresso_espresso_idling_resource",
    ],
)

See migration capabilities for supported features. In advanced cases, where entire project might not be migratable, it migrates part of the graph and sets up hybrid build where part of the graph can be built with Bazel and rest with Gradle.

Features

  • Generate BUILD.bazel, WORKSPACE for given Android project and reduce the overall migration effort.
  • Setup hybrid build to build part of project graph to build with Bazel and rest with Gradle.
  • Minimal source changes to codebase - supported by Grab Bazel Common.
  • Gradle Configuration as source of truth.

Components

  • Gradle plugin
  • A Kotlin Starlark DSL to generate Starlark code in a type-safe way.
  • Grab Bazel Common - Custom rules to bridge the gap between Gradle/Bazel.

Getting Started

Requirements

  • Buildifier is installed and avaialble in the path.

Install via homebrew. 

brew install buildifier

Install via apt and npm. 

sudo apt-get install nodejs npm
npm i -g @bazel/buildifier

Apply Grazel plugin

Grazel is available on Maven Central.

Maven Central

In root build.gradle:

buildscript {
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath "com.grab.grazel:grazel-gradle-plugin:0.2.0"
    }
}
apply plugin: "com.grab.grazel"

// Grazel configuration
grazel {
    // DSL
}

Note

Grazel registers migrateToBazel lifecycle task that can be used to generate Bazel build scripts. By default, it filters out modules based on a set of migration criteria and generates scripts only for supported modules.

To run Grazel, execute

./gradlew migrateToBazel

For more advanced configuration options, see Configuration.

License

Copyright 2021 Grabtaxi Holdings PTE LTE (GRAB)

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.