really assert that directory index is initialized inside a read action

otherwise roots can become invalid during its creation and be cached so

also fix one offender and add contracts to prevent similar assert/is typos in future

platform/core-api/src/com/intellij/openapi/application/Application.java

@@ -22,6 +22,7 @@ import com.intellij.openapi.util.Computable;
 import com.intellij.openapi.util.Condition;
 import com.intellij.openapi.util.ThrowableComputable;
 import com.intellij.util.ThrowableRunnable;
+import org.jetbrains.annotations.Contract;
 import org.jetbrains.annotations.NotNull;
 
 import java.awt.*;
@@ -166,6 +167,7 @@ public interface Application extends ComponentManager {
    * @see #assertWriteAccessAllowed()
    * @see #runWriteAction(Runnable)
    */
+  @Contract(pure=true)
   boolean isWriteAccessAllowed();
 
   /**
@@ -175,6 +177,7 @@ public interface Application extends ComponentManager {
    * @see #assertReadAccessAllowed()
    * @see #runReadAction(Runnable)
    */
+  @Contract(pure=true)
   boolean isReadAccessAllowed();
 
   /**
@@ -182,6 +185,7 @@ public interface Application extends ComponentManager {
    *
    * @return true if the current thread is the Swing dispatch thread, false otherwise.
    */
+  @Contract(pure=true)
   boolean isDispatchThread();
 
   /**

platform/indexing-api/src/com/intellij/util/indexing/FileBasedIndex.java

@@ -16,6 +16,7 @@
 package com.intellij.util.indexing;
 
 import com.intellij.openapi.application.ApplicationManager;
+import com.intellij.openapi.application.ReadAction;
 import com.intellij.openapi.fileTypes.FileType;
 import com.intellij.openapi.progress.ProgressIndicator;
 import com.intellij.openapi.project.Project;
@@ -168,7 +169,7 @@ public abstract class FileBasedIndex {
         if (visitedRoots != null && !root.equals(file) && file.isDirectory() && !visitedRoots.add(file)) {
           return false;
         }
-        if (projectFileIndex != null && projectFileIndex.isExcluded(file)) {
+        if (projectFileIndex != null && ReadAction.compute(() -> projectFileIndex.isExcluded(file))) {
           return false;
         }
         return true;

platform/projectModel-impl/src/com/intellij/openapi/roots/impl/RootIndex.java

@@ -75,7 +75,7 @@ public class RootIndex {
     myProject = project;
     myInfoCache = cache;
 
-    ApplicationManager.getApplication().isReadAccessAllowed();
+    ApplicationManager.getApplication().assertReadAccessAllowed();
 
     final RootInfo info = buildRootInfo(project);