KotlinApiBuildTask finds extension by itself looking up in the project hierarchy

If there's an ApiValidationExtension somewhere in the project or in its parent projects,
it uses its properties as defaults for the corresponding task properties.
It is still possible to instantiate a task without extension and to set or override properties
individually.

Author: ilya-g

src/main/kotlin/BinaryCompatibilityValidatorPlugin.kt

@@ -199,16 +199,19 @@ private fun Project.configureKotlinCompilation(
                 files(provider<Any> { if (isEnabled) compilation.compileDependencyFiles else emptyList<Any>() })
         }
         outputApiDir = apiBuildDir.get()
-        ignoredPackages = extension.ignoredPackages
-        ignoredClasses = extension.ignoredClasses
-        nonPublicMarkers = extension.nonPublicMarkers
     }
     configureCheckTasks(apiBuildDir, apiBuild, extension, targetConfig, commonApiDump, commonApiCheck)
 }
 
 val Project.sourceSets: SourceSetContainer
     get() = convention.getPlugin(JavaPluginConvention::class.java).sourceSets
 
+internal val Project.apiValidationExtensionOrNull: ApiValidationExtension?
+    get() =
+        generateSequence(this) { it.parent }
+            .map { it.extensions.findByType(ApiValidationExtension::class.java) }
+            .firstOrNull { it != null }
+
 fun apiCheckEnabled(projectName: String, extension: ApiValidationExtension): Boolean =
     projectName !in extension.ignoredProjects && !extension.validationDisabled
 
@@ -227,9 +230,6 @@ private fun Project.configureApiTasks(
         inputClassesDirs = files(provider<Any> { if (isEnabled) sourceSet.output.classesDirs else emptyList<Any>() })
         inputDependencies = files(provider<Any> { if (isEnabled) sourceSet.output.classesDirs else emptyList<Any>() })
         outputApiDir = apiBuildDir.get()
-        ignoredPackages = extension.ignoredPackages
-        ignoredClasses = extension.ignoredClasses
-        nonPublicMarkers = extension.nonPublicMarkers
     }
 
     configureCheckTasks(apiBuildDir, apiBuild, extension, targetConfig)

src/main/kotlin/KotlinApiBuildTask.kt

@@ -16,6 +16,8 @@ import javax.inject.Inject
 open class KotlinApiBuildTask @Inject constructor(
 ) : DefaultTask() {
 
+    private val extension = project.apiValidationExtensionOrNull
+
     @InputFiles
     @Optional
     @PathSensitive(PathSensitivity.RELATIVE)
@@ -33,14 +35,23 @@ open class KotlinApiBuildTask @Inject constructor(
     @OutputDirectory
     lateinit var outputApiDir: File
 
+    private var _ignoredPackages: Set<String>? = null
     @get:Input
-    var ignoredPackages : Set<String> = emptySet()
+    var ignoredPackages : Set<String>
+        get() = _ignoredPackages ?: extension?.ignoredPackages ?: emptySet()
+        set(value) { _ignoredPackages = value }
 
+    private var _nonPublicMarkes: Set<String>? = null
     @get:Input
-    var nonPublicMarkers : Set<String> = emptySet()
+    var nonPublicMarkers : Set<String>
+        get() = _nonPublicMarkes ?: extension?.nonPublicMarkers ?: emptySet()
+        set(value) { _nonPublicMarkes = value }
 
+    private var _ignoredClasses: Set<String>? = null
     @get:Input
-    var ignoredClasses : Set<String> = emptySet()
+    var ignoredClasses : Set<String>
+        get() = _ignoredClasses ?: extension?.ignoredClasses ?: emptySet()
+        set(value) { _ignoredClasses = value }
 
     @get:Internal
     internal val projectName = project.name