Deduplicate logic of computing orphan source sets in MPP Gradle Import

Set of compiled source sets is already available in
MultiplatformModelImportingContext via
'sourceSetsToParticipatedCompilations.keys', no need to recompute it

^KT-37127

idea/kotlin-gradle-tooling/src/KotlinMPPGradleModelBuilder.kt

@@ -84,15 +84,7 @@ class KotlinMPPGradleModelBuilder : ModelBuilderService {
     ): Map<String, KotlinSourceSetImpl> {
         if (importingContext.getProperty(IMPORT_ORPHAN_SOURCE_SETS)) return importingContext.sourceSetsByNames
 
-        // TODO: similar to importingContext.sourceSetsByCompilations.keys, will be deduplicated in further commits
-        val compiledSourceSets: Collection<String> =
-            importingContext.targets
-                .flatMap { it.compilations }
-                .flatMap { it.sourceSets }
-                .flatMap { it.dependsOnSourceSets.union(listOf(it.name)) }
-                .distinct()
-
-        val (orphanSourceSets, nonOrphanSourceSets) = importingContext.sourceSets.partition { !compiledSourceSets.contains(it.name) }
+        val (orphanSourceSets, nonOrphanSourceSets) = importingContext.sourceSets.partition { importingContext.isOrphanSourceSet(it) }
 
         orphanSourceSets.forEach {
             logger.warn("[sync warning] Source set \"${it.name}\" is not compiled with any compilation. This source set is not imported in the IDE.")

idea/kotlin-gradle-tooling/src/MultiplatformModelImportingContext.kt

@@ -17,12 +17,25 @@ internal interface MultiplatformModelImportingContext {
 
     val targets: Collection<KotlinTarget>
     val compilations: Collection<KotlinCompilation>
-    
+
+    /**
+     * All source sets in a project, including those that are created but not included into any compilations
+     * (so-called "orphan" source sets). Use [isOrphanSourceSet] to get only compiled source sets
+     */
     val sourceSets: Collection<KotlinSourceSetImpl>
     val sourceSetsByNames: Map<String, KotlinSourceSetImpl>
 
     fun sourceSetByName(name: String): KotlinSourceSet?
     fun compilationsBySourceSet(sourceSet: KotlinSourceSet): Collection<KotlinCompilation>?
+
+    /**
+     * "Orphan" is a source set which is not actually compiled by the compiler, i.e. the one
+     * which doesn't belong to any [KotlinCompilation].
+     *
+     * Orphan source sets might appear if one creates a source-set manually and doesn't link
+     * it anywhere (essentially this is a misconfiguration)
+     */
+    fun isOrphanSourceSet(sourceSet: KotlinSourceSet): Boolean = compilationsBySourceSet(sourceSet) == null
 }
 
 internal fun MultiplatformModelImportingContext.getProperty(property: GradleImportProperties): Boolean = project.getProperty(property)
@@ -99,6 +112,9 @@ internal class MultiplatformModelImportingContextImpl(override val project: Proj
         this.targets = targets
     }
 
+    // overload for small optimization
+    override fun isOrphanSourceSet(sourceSet: KotlinSourceSet): Boolean = sourceSet in sourceSetToParticipatedCompilations.keys
+
     override fun compilationsBySourceSet(sourceSet: KotlinSourceSet): Collection<KotlinCompilation>? =
         sourceSetToParticipatedCompilations[sourceSet]