Put all stub versions into one place, explain their meaning

compiler/frontend/src/org/jetbrains/kotlin/psi/stubs/KotlinStubVersions.kt

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2010-2016 JetBrains s.r.o.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.jetbrains.kotlin.psi.stubs
+
+object KotlinStubVersions {
+
+    // Source stub version should be increased if stub format (org.jetbrains.kotlin.psi.stubs.impl) is changed
+    //      or changes are made to the parser that can potentially modify the psi structure of kotlin source code.
+    // Though only kotlin declarations (no code in the bodies) are stubbed, please do increase this version
+    //      if you are not 100% sure it can be avoided.
+    // Increasing this version will lead to reindexing of all kotlin source files on the first IDE startup with the new version.
+    const val SOURCE_STUB_VERSION = 67
+
+    // Binary stub version should be increased if stub format (org.jetbrains.kotlin.psi.stubs.impl) is changed
+    //      or changes are made to the core stub building code (org.jetbrains.kotlin.idea.decompiler.stubBuilder).
+    // Increasing this version will lead to reindexing of all binary files that are potentially kotlin binaries (including all class files).
+    private const val BINARY_STUB_VERSION = 1
+
+    // Classfile stub version should be increased if changes are made to classfile stub building subsystem (org.jetbrains.kotlin.idea.decompiler.classFile)
+    // Increasing this version will lead to reindexing of all classfiles.
+    const val CLASSFILE_STUB_VERSION = BINARY_STUB_VERSION + 0
+
+    // BuiltIn stub version should be increased if changes are made to builtIn stub building subsystem (org.jetbrains.kotlin.idea.decompiler.builtIns)
+    // Increasing this version will lead to reindexing of all builtIn files (see KotlinBuiltInFileType).
+    const val BUILTIN_STUB_VERSION = BINARY_STUB_VERSION + 1
+
+    // JS stub version should be increased if changes are made to js stub building subsystem (org.jetbrains.kotlin.idea.decompiler.js)
+    // Increasing this version will lead to reindexing of js binary files (see KotlinJavaScriptMetaFileType).
+    const val JS_STUB_VERSION = BINARY_STUB_VERSION + 0
+}

compiler/frontend/src/org/jetbrains/kotlin/psi/stubs/elements/KtFileElementType.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2015 JetBrains s.r.o.
+ * Copyright 2010-2016 JetBrains s.r.o.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -30,12 +30,11 @@ import org.jetbrains.annotations.NotNull;
 import org.jetbrains.kotlin.idea.KotlinLanguage;
 import org.jetbrains.kotlin.parsing.KotlinParser;
 import org.jetbrains.kotlin.psi.stubs.KotlinFileStub;
+import org.jetbrains.kotlin.psi.stubs.KotlinStubVersions;
 
 import java.io.IOException;
 
 public class KtFileElementType extends IStubFileElementType<KotlinFileStub> {
-    public static final int STUB_VERSION = 67;
-
     private static final String NAME = "kotlin.FILE";
 
     public KtFileElementType() {
@@ -53,7 +52,7 @@ public class KtFileElementType extends IStubFileElementType<KotlinFileStub> {
 
     @Override
     public int getStubVersion() {
-        return STUB_VERSION;
+        return KotlinStubVersions.SOURCE_STUB_VERSION;
     }
 
     @NotNull