From df075547640104db51da919707627478a798ecf1 Mon Sep 17 00:00:00 2001
From: Alexey Sedunov <alexey.sedunov@jetbrains.com>
Date: Mon, 18 Apr 2016 15:45:57 +0300
Subject: [PATCH] Find Usages: Start read action for derived class search 
 #KT-11845 Fixed

---
 ChangeLog.md                                  |  1 +
 .../handlers/KotlinFindClassUsagesHandler.kt  | 26 ++++++++++---------
 2 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/ChangeLog.md b/ChangeLog.md
index 6246cf4199e..162645720dc 100644
--- a/ChangeLog.md
+++ b/ChangeLog.md
@@ -25,6 +25,7 @@ Issues fixed:
 - [KT-11659](https://youtrack.jetbrains.com/issue/KT-11659) Generate abstract overrides for Any members inside of Kotlin interfaces
 - [KT-11866](https://youtrack.jetbrains.com/issue/KT-11866) Suggest "Create secondary constructor" when constructors exist but are not applicable
 - [KT-11908](https://youtrack.jetbrains.com/issue/KT-11866) Allow properties with custom setters to be used in generated equals/hashCode/toString
+- [KT-11845](https://youtrack.jetbrains.com/issue/KT-11845) Fixed exception on attempt to find derived classes
 
 #### Debugger
 
diff --git a/idea/src/org/jetbrains/kotlin/idea/findUsages/handlers/KotlinFindClassUsagesHandler.kt b/idea/src/org/jetbrains/kotlin/idea/findUsages/handlers/KotlinFindClassUsagesHandler.kt
index 88a09fe1d8d..0d07aa648dc 100644
--- a/idea/src/org/jetbrains/kotlin/idea/findUsages/handlers/KotlinFindClassUsagesHandler.kt
+++ b/idea/src/org/jetbrains/kotlin/idea/findUsages/handlers/KotlinFindClassUsagesHandler.kt
@@ -76,20 +76,22 @@ class KotlinFindClassUsagesHandler(
 
         fun processInheritors(): Boolean {
             val request = HierarchySearchRequest(element, options.searchScope, options.isCheckDeepInheritance)
-            return request.searchInheritors().forEach(
-                    PsiElementProcessorAdapter(
-                            object : PsiElementProcessor<PsiClass> {
-                                override fun execute(element: PsiClass): Boolean {
-                                    val isInterface = element.isInterface
-                                    return when {
-                                        isInterface && options.isDerivedInterfaces || !isInterface && options.isDerivedClasses ->
-                                            KotlinFindUsagesHandler.processUsage(processor, element.navigationElement)
-                                        else -> true
+            return runReadAction {
+                request.searchInheritors().forEach(
+                        PsiElementProcessorAdapter(
+                                object : PsiElementProcessor<PsiClass> {
+                                    override fun execute(element: PsiClass): Boolean {
+                                        val isInterface = element.isInterface
+                                        return when {
+                                            isInterface && options.isDerivedInterfaces || !isInterface && options.isDerivedClasses ->
+                                                KotlinFindUsagesHandler.processUsage(processor, element.navigationElement)
+                                            else -> true
+                                        }
                                     }
                                 }
-                            }
-                    )
-            )
+                        )
+                )
+            }
         }
 
         val classOrObject = element as KtClassOrObject