Try to diagnose NoDescriptorForDeclarationException in completion

idea/idea-analysis/src/org/jetbrains/kotlin/idea/project/IdeaEnvironment.kt

@@ -24,5 +24,6 @@ object IdeaEnvironment : TargetEnvironment("Idea") {
     override fun configure(container: StorageComponentContainer) {
         container.useImpl<ResolveElementCache>()
         container.useImpl<IdeaLocalDescriptorResolver>()
+        container.useImpl<IdeaAbsentDescriptorHandler>()
     }
 }

idea/idea-analysis/src/org/jetbrains/kotlin/idea/project/IdeaLocalDescriptorResolver.kt

@@ -17,18 +17,33 @@
 package org.jetbrains.kotlin.idea.project
 
 import org.jetbrains.kotlin.descriptors.DeclarationDescriptor
+import org.jetbrains.kotlin.idea.stubindex.resolve.PluginDeclarationProviderFactory
 import org.jetbrains.kotlin.psi.KtDeclaration
 import org.jetbrains.kotlin.resolve.BindingContext
 import org.jetbrains.kotlin.resolve.lazy.BodyResolveMode
 import org.jetbrains.kotlin.resolve.lazy.LocalDescriptorResolver
+import org.jetbrains.kotlin.resolve.lazy.AbsentDescriptorHandler
 import org.jetbrains.kotlin.resolve.lazy.NoDescriptorForDeclarationException
+import org.jetbrains.kotlin.resolve.lazy.declarations.DeclarationProviderFactory
 
 class IdeaLocalDescriptorResolver(
-        private val resolveElementCache: ResolveElementCache
-): LocalDescriptorResolver {
+        private val resolveElementCache: ResolveElementCache,
+        private val absentDescriptorHandler: AbsentDescriptorHandler
+) : LocalDescriptorResolver {
     override fun resolveLocalDeclaration(declaration: KtDeclaration): DeclarationDescriptor {
         val context = resolveElementCache.resolveToElement(declaration, BodyResolveMode.FULL)
         return context.get(BindingContext.DECLARATION_TO_DESCRIPTOR, declaration)
-            ?: throw NoDescriptorForDeclarationException(declaration)
+               ?: absentDescriptorHandler.diagnoseDescriptorNotFound(declaration)
+    }
+}
+
+class IdeaAbsentDescriptorHandler(
+        private val declarationProviderFactory: DeclarationProviderFactory
+) : AbsentDescriptorHandler {
+    override fun diagnoseDescriptorNotFound(declaration: KtDeclaration): DeclarationDescriptor {
+        throw NoDescriptorForDeclarationException(
+                declaration,
+                (declarationProviderFactory as? PluginDeclarationProviderFactory)?.debugToString()
+        )
     }
 }

idea/idea-analysis/src/org/jetbrains/kotlin/idea/stubindex/resolve/PluginDeclarationProviderFactory.kt

@@ -58,4 +58,24 @@ class PluginDeclarationProviderFactory(
         throw IllegalStateException("Cannot find package fragment for file ${file.name} with package ${file.packageFqName}, " +
                                     "vFile ${file.virtualFile}, nonIndexed ${file in nonIndexedFiles}")
     }
+
+    // trying to diagnose org.jetbrains.kotlin.resolve.lazy.NoDescriptorForDeclarationException in completion
+    private val onCreationDebugInfo = debugInfo()
+
+    fun debugToString(): String {
+        return "PluginDeclarationProviderFactory\nOn failure:\n${debugInfo()}On creation:\n$onCreationDebugInfo"
+    }
+
+    private fun debugInfo(): String {
+        if (nonIndexedFiles.isEmpty()) return "-no synthetic files-\n"
+
+        return buildString {
+            nonIndexedFiles.forEach {
+                append(it.name)
+                append(" isPhysical=${it.isPhysical}")
+                append(" modStamp=${it.modificationStamp}")
+                appendln()
+            }
+        }
+    }
 }