Gradle: Your Build, Your Rules

Talk by Aurimas Liutikas at DPE Summit 2025 in San Francisco

Transcript

1. Gradle: Your Build, Your Rules Aurimas Liutikas / AndroidX @ Google @aurimas@androiddev.social
2. Target Audience You use Gradle
3. Target Audience You use Gradle You have a build team
4. Target Audience You use Gradle You have a build team Care about consistency
5. Target Audience You use Gradle You have a build team Care about consistency Can no longer review every build.gradle.kts change
6. “With great power comes great responsibility” from Spider-Man comic
7. “Gradle is very powerful” from Aurimas
8. People are lazy. Use conventions Level of strictness Low High
9. plugins { id("com.android.library") id("org.jetbrains.kotlin.android") } android { namespace = "com.example.mylibrary" compileSdk = 36 defaultConfig { minSdk = 24 testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner" consumerProguardFiles("consumer-rules.pro") } buildTypes { release { isMinifyEnabled = false proguardFiles( getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro" ) } } compileOptions { sourceCompatibility = JavaVersion.VERSION_11 targetCompatibility = JavaVersion.VERSION_11 } kotlinOptions { jvmTarget = "11" } } dependencies { implementation(libs.androidx.core.ktx) implementation(libs.androidx.appcompat) implementation(libs.material) testImplementation(libs.junit) androidTestImplementation(libs.androidx.junit) androidTestImplementation(libs.androidx.espresso.core) }
10. Leave only dependencies {} and custom extension plugins { id("FancyPlugin") id("com.android.library") } dependencies { implementation("foo:bar:1.0.0") } fancy { allowedToggleFoo = true
11. Leave only dependencies {} and custom extension dependencies { implementation("foo:bar:1.0.0") } fancy { allowedToggleFoo = true allowedToggleBar = true }
12. Leave only dependencies {} and custom extension dependencies { implementation("foo:bar:1.0.0") } fancy { allowedToggleFoo = true allowedToggleBar = true }
13. Let machines help you filter Level of strictness Low High
14. Add reviewers for change patterns For changes outside of dependencies and fancy DSLs automatically add reviewers from the build team banana { allowedToggleFoo = true allowedToggleBar = true } android { compileSdk = 36 }
15. banana { allowedToggleFoo = true allowedToggleBar = true } android { compileSdk = 36 } Add reviewers for change patterns REST API call /repos/{owner}/{repo}/ pulls/{pull_number}/ requested_reviewers
16. Enforce DSL that uses Property API Level of strictness Low High
17. Modern plugins use Property<> API kotlin { compilerOptions.jvmTarget = JvmTarget.JVM_17 }
18. disallowChanges on DSL properties private fun <T : Any> Property<T>.setAndDisallow( newValue: T ) { set(newValue) disallowChanges() }
19. disallowChanges on DSL properties private fun Project.configureKotlin() { val kotlin = extensions.getByType( KotlinAndroidExtension::class.java ) kotlin.compilerOptions.jvmTarget.setAndDisallow( JvmTarget.JVM_1_8 ) }
20. disallowChanges on DSL properties FAILURE: Build failed with an exception. * Where: Build file 'your-build-your-rules/build.gradle.kts' line: 45 * What went wrong: The value for property 'jvmTarget' cannot be changed any further. ❌
21. Enforce Android Gradle Plugin DSL Level of strictness Low High
22. finalizeDsl for Android projects private fun Project.configureAppPlugin() { val android = extensions.getByType( ApplicationAndroidComponentsExtension::class.java ) android.finalizeDsl { it.compileSdk = 36 } }
23. No-op from build.gradle.kts android { compileSdk = 35 } ❌
24. Enforce legacy plugins Level of strictness Low High
25. Last resort afterEvaluate private fun Project.configureJavaPlugin() { val java = extensions.getByType( JavaPluginExtension::class.java) afterEvaluate { java.sourceCompatibility = JavaVersion.VERSION_1_8 java.targetCompatibility = JavaVersion.VERSION_1_8 } }
26. No-op from build.gradle.kts java { sourceCompatibility = JavaVersion.VERSION_11 targetCompatibility = JavaVersion.VERSION_11 } ❌
27. What about “creative” build.gradle.kts?
28. afterEvaluate { androidComponents.finalizeDsl { it.compileSdk = 35 } } afterEvaluate { afterEvaluate { java.sourceCompatibility = JavaVersion.VERSION_17 java.targetCompatibility = JavaVersion.VERSION_17 } }
29. Need to go deeper - validation tasks Level of strictness Low High
30. Extension validation abstract class DslValidationTask : DefaultTask() { @get:Input abstract val testRunner: Property<String> @TaskAction fun validate() { if (testRunner.get() != EXPECTED_TEST_RUNNER) throw Exception("Use $EXPECTED_TEST_RUNNER!") } } private const val EXPECTED_TEST_RUNNER = "androidx.test..."
31. private fun Project.configureAppPlugin() { val android = extensions.getByType( ApplicationExtension::class.java) val testRunner = provider { android.defaultConfig.testInstrumentationRunner } tasks.register( "validateDsl", DslValidationTask::class.java) { it.testRunner.set(testRunner) } }
32. Extension validation android { defaultConfig { testInstrumentationRunner = "com.BadRunner" } } * What went wrong: Execution failed for task ':app:validateDsl'. > java.lang.Exception: Use androidx.test.runner.AndroidJUnitRunner ❌
33. Even further? Validating task outputs Level of strictness Low High
34. Task output validation abstract class ValidateManifestTask : DefaultTask() { @get:InputFile abstract val manifest: RegularFileProperty @TaskAction fun validate() { if (!manifest.get().asFile.readText().contains( """<uses-sdk android:minSdkVersion="24" />""" )) throw Exception("minSdkVersion was not set to 24") } }
35. Task output validation private fun Project.configureAndroidLibraryPlugin() { extensions.getByType( LibraryAndroidComponentsExtension::class.java ).onVariants { tasks.register("validateManifest${it.name}", ValidateManifestTask::class.java) { task -> task.manifest.set( it.artifacts.get(SingleArtifact.MERGED_MANIFEST)) } } }
36. Task output validation android { defaultConfig { minSdk = 30 } } * What went wrong: Execution failed for task ':lib:validateManifestdebug'. > java.lang.Exception: minSdkVersion was not set to 24 ❌
37. Validating build.gradle.kts contents Level of strictness Low High
38. build.gradle.kts content validation abstract class ValidateBuildGradleTask : DefaultTask() { @get:InputFile abstract val build: RegularFileProperty @TaskAction fun validate() { val buildContents = build.get().asFile.readText() if (buildContents.contains("kotlin {")) throw Exception("Do not configure Kotlin ...") } }
39. build.gradle.kts content validation project.tasks.register( "validateBuildGradle", ValidateBuildGradleTask::class.java ) { task -> task.buildGradle.set( project.layout.projectDirectory.file("build.gradle.kts") ) }
40. build.gradle.kts content validation kotlin { // any configuration } * What went wrong: Execution failed for task ':app:validateBuildGradle'. > java.lang.Exception: Do not configure Kotlin plugin directly. ❌
41. build.gradle (groovy) content validation plugins { id("nebula-lint") version “21.1.1” } gradleLint { rules += ... }
42. Strict build configuration Level of strictness Low High
43. Move to a custom build.json definition file { "type": "androidLibrary", "dependencies": { "implementation": [ "androidx.annotation:annotation:1.9.1" ] } }
44. Basic model of JSON using moshi @JsonClass(generateAdapter = true) data class BuildFile( val type: ProjectType, val dependencies: Dependencies, ) enum class ProjectType { androidLibrary, androidApplication } @JsonClass(generateAdapter = true) data class Dependencies(val implementation: List<String>)
45. Parse the JSON class JsonProjectPlugin : Plugin<Project> { override fun apply(project: Project) { val buildJsonFile = project.layout.projectDirectory.file("build.json").asFile val moshi: Moshi = Moshi.Builder().build() val jsonAdapter = moshi.adapter<BuildFile>() val build = jsonAdapter.fromJson(buildJsonFile.readText())!! // ..
46. Configure based on build.json class JsonProjectPlugin : Plugin<Project> { override fun apply(project: Project) { // .. val build = jsonAdapter.fromJson(buildJsonFile.readText())!! when (build.type) { ProjectType.androidLibrary -> project.library(build) ProjectType.androidApplication -> project.app(build) } }
47. Configure based on build.json private fun Project.library(build: BuildFile) { configureKotlin() plugins.apply("com.android.library") configureAndroidCommon() build.dependencies.implementation.forEach { dep -> dependencies.add("implementation", dep) } }
48. Apply the plugin in root build.gradle.kts allprojects { if (isStrictProject(path)) { plugins.apply("JsonProjectPlugin") } }
49. That’s kind of it
50. Other formats - YAML type: androidLibrary dependencies: - implementation: - androidx.annotation:annotation:1.9.1
51. Other formats - XML <?xml version="1.0" encoding="UTF-8"?> <androidLibrary> <dependencies> <implementation> androidx.annotation:annotation:1.9.1 </implementation> </dependencies> </androidLibrary>
52. JSON5, starlark, TOML, …
53. Could Gradle natively support these?
54. Declarative Gradle javaApplication { javaVersion = 21 mainClass = "com.example.App" dependencies { implementation(project(":java-util")) implementation("com.google.guava:guava:32.1.3-jre") } }
55. Still EAP, long road ahead of it
56. What have we learned?
57. Takeaways Many ways to enforce consistency
58. Takeaways Many ways to enforce consistency As build grows strictness tends to increase
59. Takeaways Many ways to enforce consistency As build grows strictness tends to increase Pick the strictness based on the severity of making a mistake
60. Takeaways Many ways to enforce consistency As build grows strictness tends to increase Pick the strictness based on the severity of making a mistake build.gradle(.kts) is not required to configure projects
61. Things we didn’t talk about Dependency locking, substitution, blocking
62. Things we didn’t talk about Dependency locking, substitution, blocking Versioning of projects
63. Things we didn’t talk about Dependency locking, substitution, blocking Versioning of projects Locking repositories used
64. Things we didn’t talk about Dependency locking, substitution, blocking Versioning of projects Locking repositories used Allowlist of Gradle plugins
65. Things we didn’t talk about Dependency locking, substitution, blocking Versioning of projects Locking repositories used Allowlist of Gradle plugins Static analysis of Gradle plugins …
66. Thank you! github.com/liutikas/your-build-your-rules