Add a shortcut for Gradle's providers

Author: dmdashenkov

gradle-api/src/main/kotlin/io/spine/protodata/gradle/CodegenSettings.kt

@@ -27,6 +27,7 @@
 package io.spine.protodata.gradle
 
 import com.google.common.collect.Multimap
+import org.gradle.api.provider.Provider
 import org.gradle.api.tasks.SourceSet
 
 /**
@@ -79,6 +80,15 @@ public interface CodegenSettings {
      */
     public val paths: Multimap<String, SourcePaths>
 
+    /**
+     * Configures a particular launch of ProtoData for the given source set.
+     *
+     * @param sourceSet the source set for which ProtoData is launched.
+     * @param configure the block configuring the launch.
+     */
+    public fun launchFor(sourceSet: Provider<SourceSet>, configure: Launch.() -> Unit): Unit =
+        launchFor(sourceSet.get().name, configure)
+
     /**
      * Configures a particular launch of ProtoData for the given source set.
      *

gradle-plugin/src/functionalTest/resources/custom-paths/build.gradle.kts

@@ -63,7 +63,7 @@ protoData {
         }
     }
 
-    launchFor(sourceSets.test.get()) {
+    launchFor(sourceSets.test) {
         sourceFileSet {
             source = "$buildDir/generated-proto/test/kotlin"
             target = "$buildDir/footest"