Provide toString() for classes that extend GlobalSearchScope (to diagnose package fragment errors)

compiler/frontend/src/org/jetbrains/kotlin/resolve/lazy/declarations/DeclarationProviderFactoryService.kt

@@ -18,12 +18,12 @@ package org.jetbrains.kotlin.resolve.lazy.declarations
 
 import com.intellij.openapi.components.ServiceManager
 import com.intellij.openapi.project.Project
+import com.intellij.openapi.vfs.VirtualFile
 import com.intellij.psi.search.DelegatingGlobalSearchScope
 import com.intellij.psi.search.GlobalSearchScope
 import org.jetbrains.kotlin.psi.KtFile
 import org.jetbrains.kotlin.storage.StorageManager
-import com.intellij.openapi.vfs.VirtualFile
-import java.util.HashSet
+import java.util.*
 
 abstract class DeclarationProviderFactoryService {
 
@@ -60,5 +60,7 @@ abstract class DeclarationProviderFactoryService {
         private val originals = syntheticFiles.mapNotNullTo(HashSet<VirtualFile>()) { it.originalFile.virtualFile }
 
         override fun contains(file: VirtualFile) = super.contains(file) && file !in originals
+
+        override fun toString() = "SyntheticFilesFilteringScope($myBaseScope)"
     }
 }