in custom file types, don't complete keywords in literals or comments (IDEA-117226)

java/java-tests/testData/codeInsight/completion/customFileType/foo.cs

@@ -0,0 +1 @@
+// ca<caret>

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

@@ -37,6 +37,11 @@ public class CustomFileTypeCompletionTest extends LightCompletionTestCase {
     testByCount(2, "case", "catch");
   }
 
+  public void testComment() throws Throwable {
+    configureByFile(BASE_PATH + "foo.cs");
+    testByCount(0, new String[] { null });
+  }
+
   public void testPlainTextSubstitution() throws IOException {
     FileTypeManagerEx.getInstanceEx().registerFileType(MockLanguageFileType.INSTANCE, "xxx");
     try {

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

@@ -17,8 +17,12 @@ package com.intellij.codeInsight.completion;
 
 import com.intellij.codeInsight.lookup.LookupElementBuilder;
 import com.intellij.ide.highlighter.custom.SyntaxTable;
+import com.intellij.openapi.editor.ex.EditorEx;
+import com.intellij.openapi.editor.highlighter.HighlighterIterator;
 import com.intellij.openapi.fileTypes.impl.CustomSyntaxTableFileType;
+import com.intellij.psi.CustomHighlighterTokenType;
 import com.intellij.psi.PsiElement;
+import com.intellij.psi.tree.IElementType;
 import com.intellij.util.ProcessingContext;
 import org.jetbrains.annotations.NotNull;
 
@@ -39,6 +43,10 @@ public class CustomFileTypeCompletionContributor extends CompletionContributor {
              protected void addCompletions(@NotNull CompletionParameters parameters,
                                            ProcessingContext context,
                                            @NotNull CompletionResultSet result) {
+               if (inCommentOrLiteral(parameters)) {
+                 return;
+               }
+
                CustomSyntaxTableFileType fileType = (CustomSyntaxTableFileType)parameters.getOriginalFile().getFileType();
                SyntaxTable syntaxTable = fileType.getSyntaxTable();
                String prefix = findPrefix(parameters.getPosition(), parameters.getOffset());
@@ -52,6 +60,19 @@ public class CustomFileTypeCompletionContributor extends CompletionContributor {
            });
   }
 
+  private static boolean inCommentOrLiteral(CompletionParameters parameters) {
+    HighlighterIterator iterator = ((EditorEx)parameters.getEditor()).getHighlighter().createIterator(parameters.getOffset());
+    IElementType elementType = iterator.getTokenType();
+    if (elementType == CustomHighlighterTokenType.WHITESPACE) {
+      iterator.retreat();
+      elementType = iterator.getTokenType();
+    }
+    return elementType == CustomHighlighterTokenType.LINE_COMMENT ||
+           elementType == CustomHighlighterTokenType.MULTI_LINE_COMMENT ||
+           elementType == CustomHighlighterTokenType.STRING ||
+           elementType == CustomHighlighterTokenType.SINGLE_QUOTED_STRING;
+  }
+
   private static void addVariants(CompletionResultSet resultSet, Set<String> keywords) {
     for (String keyword : keywords) {
       resultSet.addElement(LookupElementBuilder.create(keyword));