Do not highlight errors in Kotlin files outside source roots

idea/src/META-INF/plugin.xml

@@ -199,6 +199,7 @@
 
     <annotator language="jet" implementationClass="org.jetbrains.jet.plugin.highlighter.JetPsiChecker"/>
     <annotator language="jet" implementationClass="org.jetbrains.jet.plugin.highlighter.DebugInfoAnnotator"/>
+    <problemHighlightFilter implementation="org.jetbrains.jet.plugin.highlighter.KotlinProblemHighlightFilter"/>
 
     <extendWordSelectionHandler implementation="org.jetbrains.jet.plugin.editor.wordSelection.JetStatementGroupSelectioner"/>
     <extendWordSelectionHandler implementation="org.jetbrains.jet.plugin.editor.wordSelection.JetCodeBlockSelectioner"/>

idea/src/org/jetbrains/jet/plugin/highlighter/KotlinProblemHighlightFilter.kt

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2010-2013 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.jet.plugin.highlighter
+
+import com.intellij.codeInsight.daemon.ProblemHighlightFilter
+import com.intellij.psi.PsiFile
+import com.intellij.ide.projectView.impl.ProjectRootsUtil
+import org.jetbrains.jet.plugin.JetFileType
+
+class KotlinProblemHighlightFilter : ProblemHighlightFilter() {
+
+    override fun shouldHighlight(psiFile: PsiFile): Boolean {
+        return psiFile.getFileType() != JetFileType.INSTANCE || !ProjectRootsUtil.isOutsideSourceRoot(psiFile)
+    }
+
+}