Add better diagnostic for "could not create stub for nested class" failures

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/builtIns/KotlinBuiltInStubBuilder.kt

@@ -81,7 +81,7 @@ public class KotlinBuiltInStubBuilder : ClsStubBuilder() {
     private fun createStubBuilderComponents(file: VirtualFile, packageFqName: FqName, nameResolver: NameResolver): ClsStubBuilderComponents {
         val finder = DirectoryBasedClassDataFinder(file.parent!!, packageFqName, nameResolver, BuiltInsSerializedResourcePaths)
         val annotationLoader = AnnotationLoaderForStubBuilderImpl(BuiltInSerializerProtocol)
-        return ClsStubBuilderComponents(finder, annotationLoader)
+        return ClsStubBuilderComponents(finder, annotationLoader, file)
     }
 
     companion object {

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/classFile/KotlinClsStubBuilder.kt

@@ -102,7 +102,7 @@ public open class KotlinClsStubBuilder : ClsStubBuilder() {
         val classFinder = DirectoryBasedClassFinder(file.getParent()!!, packageFqName)
         val classDataFinder = DirectoryBasedDataFinder(classFinder, LOG)
         val annotationLoader = AnnotationLoaderForClassFileStubBuilder(classFinder, LoggingErrorReporter(LOG))
-        return ClsStubBuilderComponents(classDataFinder, annotationLoader)
+        return ClsStubBuilderComponents(classDataFinder, annotationLoader, file)
     }
 
     companion object {

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/js/KotlinJavaScriptStubBuilder.kt

@@ -82,6 +82,6 @@ public class KotlinJavaScriptStubBuilder : ClsStubBuilder() {
                 file.parent!!, packageFqName, nameResolver, KotlinJavascriptSerializedResourcePaths
         )
         val annotationLoader = AnnotationLoaderForStubBuilderImpl(JsSerializerProtocol)
-        return ClsStubBuilderComponents(classDataFinder, annotationLoader)
+        return ClsStubBuilderComponents(classDataFinder, annotationLoader, file)
     }
 }

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/stubBuilder/ClassClsStubBuilder.kt

@@ -16,6 +16,7 @@
 
 package org.jetbrains.kotlin.idea.decompiler.stubBuilder
 
+import com.intellij.openapi.diagnostic.Logger
 import com.intellij.psi.PsiElement
 import com.intellij.psi.stubs.StubElement
 import org.jetbrains.kotlin.builtins.KotlinBuiltIns
@@ -233,10 +234,24 @@ private class ClassClsStubBuilder(
     }
 
     private fun createNestedClassStub(classBody: StubElement<out PsiElement>, nestedClassId: ClassId) {
-        val classDataWithSource = c.components.classDataFinder.findClassData(nestedClassId).sure {
+        val classDataWithSource = c.components.classDataFinder.findClassData(nestedClassId)
-            "Could not find class data for nested class ${nestedClassId.shortClassName} of class ${nestedClassId.outerClassId}"
+        if (classDataWithSource == null) {
+            val rootFile = c.components.virtualFileForDebug
+            LOG.error(
+                    "Could not find class data for nested class $nestedClassId of class ${nestedClassId.outerClassId}\n" +
+                    "Root file: ${rootFile.canonicalPath}\n" +
+                    "Dir: ${rootFile.parent.canonicalPath}\n" +
+                    "Children:\n" +
+                    "${rootFile.parent.children.sortedBy { it.name }.joinToString(separator = "\n") {
+                        it.name + " (valid: ${it.isValid})"
+                    } }")
+            return
         }
         val (nameResolver, classProto) = classDataWithSource.classData
         createClassStub(classBody, classProto, nestedClassId, c.child(nameResolver, TypeTable(classProto.typeTable)))
     }
+
+    companion object {
+        private val LOG = Logger.getInstance(ClassClsStubBuilder::class.java)
+    }
 }

idea/idea-analysis/src/org/jetbrains/kotlin/idea/decompiler/stubBuilder/ClsStubBuilderContext.kt

@@ -16,6 +16,7 @@
 
 package org.jetbrains.kotlin.idea.decompiler.stubBuilder
 
+import com.intellij.openapi.vfs.VirtualFile
 import org.jetbrains.kotlin.descriptors.annotations.AnnotationUseSiteTarget
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.FqName
@@ -30,7 +31,8 @@ data class ClassIdWithTarget(val classId: ClassId, val target: AnnotationUseSite
 
 class ClsStubBuilderComponents(
         val classDataFinder: ClassDataFinder,
-        val annotationLoader: AnnotationAndConstantLoader<ClassId, Unit, ClassIdWithTarget>
+        val annotationLoader: AnnotationAndConstantLoader<ClassId, Unit, ClassIdWithTarget>,
+        val virtualFileForDebug: VirtualFile
 ) {
     fun createContext(
             nameResolver: NameResolver,