fix completion in an empty custom-file-type file (EA-93679 - IOOBE: SegmentArrayWithData.getSegmentData)

java/java-tests/testSrc/com/intellij/codeInsight/completion/CustomFileTypeCompletionTest.java

@@ -42,6 +42,12 @@ public class CustomFileTypeCompletionTest extends LightCompletionTestCase {
     testByCount(0, new String[] { null });
   }
 
+  public void testEmptyFile() throws Throwable {
+    configureFromFileText("a.cs", "<caret>");
+    complete();
+    testByCount(1, "abstract", "x");
+  }
+
   public void testPlainTextSubstitution() throws IOException {
     FileTypeManagerEx.getInstanceEx().registerFileType(MockLanguageFileType.INSTANCE, "xxx");
     try {

platform/lang-impl/src/com/intellij/codeInsight/completion/CustomFileTypeCompletionContributor.java

@@ -71,6 +71,8 @@ public class CustomFileTypeCompletionContributor extends CompletionContributor i
 
   private static boolean inCommentOrLiteral(CompletionParameters parameters) {
     HighlighterIterator iterator = ((EditorEx)parameters.getEditor()).getHighlighter().createIterator(parameters.getOffset());
+    if (iterator.atEnd()) return false;
+
     IElementType elementType = iterator.getTokenType();
     if (elementType == CustomHighlighterTokenType.WHITESPACE) {
       iterator.retreat();