The Benevolent Gradle Overlord: Keeping Order

Talk by Aurimas Liutikas at Droidcon London 2025

Transcript

1. The Benevolent Gradle Overlord: Keeping Order Aurimas Liutikas / AndroidX @ Google @aurimas@androiddev.social
2. Motivation
3. Build pain (tears) Project size No build team
4. Build pain (tears) Project size No build team Properly sized build team
5. Never hear about amazing build team
6. Enter 2025
7. Enter 2025 LLMs → bigger projects
8. Enter 2025 LLMs → bigger projects Reduction in staffing
9. Build pain (tears) Project size No build team Properly sized build team Lean build team
10. Build pain (tears) Project size No build team Properly sized build team Lean build team
11. The Plan
12. Agenda Build files
13. Agenda Build files Upgrades
14. Agenda Build files Upgrades Reducing bugs
15. Agenda Build files Upgrades Reducing bugs Monitor impact
16. Build files build.gradle(.kts)
17. “With great power comes great responsibility” from Spider-Man comic
18. “Gradle is very powerful” from Aurimas
19. Few people understand build.gradle(.kts)
20. Reduce software developers’ cognitive load
21. Level of strictness Low High
22. Level of strictness Low High
23. Level of strictness Low High
24. People are lazy. Use conventions Level of strictness Low High
25. 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) }
26. Leave only dependencies {} and custom extension plugins { id("FancyPlugin") id("com.android.library") } dependencies { implementation("foo:bar:1.0.0") } fancy { allowedToggleFoo = true
27. Leave only dependencies {} and custom extension dependencies { implementation("foo:bar:1.0.0") } fancy { allowedToggleFoo = true allowedToggleBar = true }
28. Leave only dependencies {} and custom extension dependencies { implementation("foo:bar:1.0.0") } fancy { allowedToggleFoo = true allowedToggleBar = true }
29. Let machines help you filter Level of strictness Low High
30. 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 }
31. banana { allowedToggleFoo = true allowedToggleBar = true } android { compileSdk = 36 } Add reviewers for change patterns REST API call /repos/{owner}/{repo}/ pulls/{pull_number}/ requested_reviewers
32. Enforce DSL that uses Property API Level of strictness Low High
33. Modern plugins use Property<> API kotlin { compilerOptions.jvmTarget = JvmTarget.JVM_17 }
34. disallowChanges on DSL properties private fun <T : Any> Property<T>.setAndDisallow( newValue: T ) { set(newValue) disallowChanges() }
35. disallowChanges on DSL properties private fun Project.configureKotlin() { val kotlin = extensions.getByType( KotlinAndroidExtension::class.java ) kotlin.compilerOptions.jvmTarget.setAndDisallow( JvmTarget.JVM_1_8 ) }
36. 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. ❌
37. Enforce Android Gradle Plugin DSL Level of strictness Low High
38. finalizeDsl for Android projects private fun Project.configureAppPlugin() { val android = extensions.getByType( ApplicationAndroidComponentsExtension::class.java ) android.finalizeDsl { it.compileSdk = 36 } }
39. No-op from build.gradle.kts android { compileSdk = 35 } ❌
40. Enforce legacy plugins Level of strictness Low High
41. 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 } }
42. No-op from build.gradle.kts java { sourceCompatibility = JavaVersion.VERSION_11 targetCompatibility = JavaVersion.VERSION_11 } ❌
43. What about “creative” build.gradle.kts?
44. afterEvaluate { androidComponents.finalizeDsl { it.compileSdk = 35 } } afterEvaluate { afterEvaluate { java.sourceCompatibility = JavaVersion.VERSION_17 java.targetCompatibility = JavaVersion.VERSION_17 } }
45. Need to go deeper - validation tasks Level of strictness Low High
46. 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 $EXPECTED_TEST_RUNNER!") } } private const val EXPECTED_TEST_RUNNER = "androidx.test..."
47. private fun Project.configureAppPlugin() { val android = extensions.getByType( ApplicationExtension::class.java) val testRunner = provider { android.defaultConfig.testInstrumentationRunner } tasks.register( "validateDsl", DslValidationTask::class.java) { it.testRunner.set(testRunner) } }
48. Extension validation android { defaultConfig { testInstrumentationRunner = "com.BadRunner" } } * What went wrong: Execution failed for task ':app:validateDsl'. > java.lang.Exception: Use androidx.test.runner.AndroidJUnitRunner ❌
49. Even further? Validating task outputs Level of strictness Low High
50. Task output validation abstract class ValidateManifestTask : DefaultTask() { @get:InputFile abstract val manifest: RegularFileProperty @TaskAction fun validate() { if (!manifest.get().asFile.readText().contains( """<uses-sdk android:minSdkVersion="24" />""" )) throw Exception("minSdkVersion was not set to 24") } }
51. Task output validation private fun Project.configureAndroidLibraryPlugin() { extensions.getByType( LibraryAndroidComponentsExtension::class.java ).onVariants { tasks.register("validateManifest${it.name}", ValidateManifestTask::class.java) { task -> task.manifest.set( it.artifacts.get(SingleArtifact.MERGED_MANIFEST)) } } }
52. 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 ❌
53. Validating build.gradle.kts contents Level of strictness Low High
54. 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 ...") } }
55. build.gradle.kts content validation project.tasks.register( "validateBuildGradle", ValidateBuildGradleTask::class.java ) { task -> task.buildGradle.set( project.layout.projectDirectory.file("build.gradle.kts") ) }
56. 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. ❌
57. build.gradle (groovy) content validation plugins { id("nebula-lint") version “21.1.1” } gradleLint { rules += ... }
58. Strict build configuration Level of strictness Low High
59. Move to a custom build.json definition file { "type": "androidLibrary", "dependencies": { "implementation": [ "androidx.annotation:annotation:1.9.1" ] } }
60. 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>)
61. 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())!! // ..
62. 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) } }
63. 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) } }
64. Apply the plugin in root build.gradle.kts allprojects { if (isStrictProject(path)) { plugins.apply("JsonProjectPlugin") } }
65. That’s kind of it
66. Other formats - YAML type: androidLibrary dependencies: - implementation: - androidx.annotation:annotation:1.9.1
67. Other formats - XML <?xml version="1.0" encoding="UTF-8"?> <androidLibrary> <dependencies> <implementation> androidx.annotation:annotation:1.9.1 </implementation> </dependencies> </androidLibrary>
68. JSON5, starlark, TOML, …
69. Could Gradle natively support these?
70. Declarative Gradle javaApplication { javaVersion = 21 mainClass = "com.example.App" dependencies { implementation(project(":java-util")) implementation("com.google.guava:guava:32.1.3-jre") } }
71. Still EAP, long road ahead of it
76. Upgrades, Upgrades, Upgrades
77. Things to keep up to date JDK
78. Things to keep up to date JDK Gradle
79. Things to keep up to date JDK Gradle Android Gradle Plugin
80. Things to keep up to date JDK Gradle Android Gradle Plugin Kotlin Gradle Plugin
81. Things to keep up to date JDK Gradle Android Gradle Plugin Kotlin Gradle Plugin Kotlin Symbol Processors
82. Things to keep up to date JDK Gradle Android Gradle Plugin Kotlin Gradle Plugin Kotlin Symbol Processors Testing tools
83. Things to keep up to date JDK Gradle Android Gradle Plugin Kotlin Gradle Plugin Kotlin Symbol Processors Testing tools …
89. …
91. From Reactive to Proactive
92. ⏭ Skip-version upgrades are harder
93. Skip-version upgrades are harder favoriteApi = true @Deprecated( “use betterApi”) favoriteApi = true betterApi = true betterApi = true AGP 8.4.3 AGP 8.13.0 AGP 9.0.0
94. 🌚 Shadow Jobs
95. 📣 Complain to tool and library owners
96. Reduce exposure
97. Reducing bugs
98. 🤖 Automate enforcement
99. 🔍 Static analysis FTW
100. Static analysis FTW Android Lint (for both Android and JVM code)
101. Static analysis FTW Android Lint (for both Android and JVM code) detekt
102. Static analysis FTW Android Lint (for both Android and JVM code) detekt ktlint
103. Static analysis FTW Android Lint (for both Android and JVM code) detekt ktlint Error-prone
104. Static analysis FTW Android Lint (for both Android and JVM code) detekt ktlint Error-prone nebula.lint
105. Contribute to Open Source
106. Always pick up latest bugfix versions
107. Monitor impact
108. Pick relevant metrics
109. Pick relevant metrics Inner loop cycle time
110. Pick relevant metrics Inner loop cycle time Time from upload to merge
111. Pick relevant metrics Inner loop cycle time Time from upload to merge Days behind latest Gradle version
112. Pick relevant metrics Inner loop cycle time Time from upload to merge Days behind latest Gradle version CSAT
113. Track Over Time
114. Foster Culture of High Expectations
115. ♻ Gain social capital to spend
116. What have we learned?
117. Takeaways Pick the strictness based on the severity of making a mistake
118. Takeaways Pick the strictness based on the severity of making a mistake build.gradle(.kts) is not required to configure projects
119. Takeaways Pick the strictness based on the severity of making a mistake build.gradle(.kts) is not required to configure projects Be proactive about your upgrades
120. Takeaways Pick the strictness based on the severity of making a mistake build.gradle(.kts) is not required to configure projects Be proactive about your upgrades Give feedback to tool & library owners
121. Takeaways Pick the strictness based on the severity of making a mistake build.gradle(.kts) is not required to configure projects Be proactive about your upgrades Give feedback to tool & library owners Automate enforcement using tasks and static analysis
122. Takeaways Pick the strictness based on the severity of making a mistake build.gradle(.kts) is not required to configure projects Be proactive about your upgrades Give feedback to tool & library owners Automate enforcement using tasks and static analysis Monitor your impact to gain social capital
123. Takeaways Pick the strictness based on the severity of making a mistake build.gradle(.kts) is not required to configure projects Be proactive about your upgrades Give feedback to tool & library owners Automate enforcement using tasks and static analysis Monitor your impact to gain social capital Profit £££
124. Build pain (tears) Project size No build team Properly sized build team Lean build team
125. Thank you! github.com/liutikas/your-build-your-rules