1. Ability to be notified about whitespaces being skipped by default PsiBuilder whitespace skipper.

2. Cheap lookAhead implementation for the PsiBuilder.

java/java-impl/src/com/intellij/lang/java/parser/JavaParserUtil.java

@@ -313,6 +313,21 @@ public class JavaParserUtil {
       myDelegate.setTokenTypeRemapper(remapper);
     }
 
+    @Override
+    public void setWhitespaceSkippedCallback(WhitespaceSkippedCallback callback) {
+      myDelegate.setWhitespaceSkippedCallback(callback);
+    }
+
+    @Override
+    public void remapCurrentToken(IElementType type) {
+      myDelegate.remapCurrentToken(type);
+    }
+
+    @Override
+    public IElementType lookAhead(int steps) {
+      return myDelegate.lookAhead(steps);
+    }
+
     @Nullable @NonNls
     public String getTokenText() {
       return myDelegate.getTokenText();
@@ -374,4 +389,4 @@ public class JavaParserUtil {
       myDelegate.putUserDataUnprotected(key, value);
     }
   }
-}
+}

platform/lang-api/src/com/intellij/lang/PsiBuilder.java

@@ -68,6 +68,25 @@ public interface PsiBuilder extends UserDataHolder, UserDataHolderUnprotected {
    */
   void setTokenTypeRemapper(ITokenTypeRemapper remapper);
 
+  /**
+   * Slightly easier way to what {@link ITokenTypeRemapper} does. I.e. we just remap current token to given type
+   */
+  void remapCurrentToken(IElementType type);
+
+  /**
+   * Subscribe for notification on default whitespace and comments skipped events.
+   * @param callback an implementation for the callback
+   */
+  void setWhitespaceSkippedCallback(WhitespaceSkippedCallback callback);
+
+  /**
+   * See what token type is in <code>steps</code> ahead
+   * @param steps 0 is current token (i.e. the same {@link PsiBuilder#getTokenType()} returns)
+   * @return type element which getTokenType() will return if we call advance <code>steps</code> times in a row
+   */
+  @Nullable
+  IElementType lookAhead(int steps);
+
   /**
    * Returns the text of the current token from the lexer.
    *

platform/lang-api/src/com/intellij/lang/WhitespaceSkippedCallback.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2000-2010 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.
+ */
+
+/*
+ * @author max
+ */
+package com.intellij.lang;
+
+import com.intellij.psi.tree.IElementType;
+
+public interface WhitespaceSkippedCallback {
+  void onSkip(IElementType type, int start, int end);
+}

platform/lang-impl/src/com/intellij/lang/impl/PsiBuilderImpl.java

@@ -93,6 +93,8 @@ public class PsiBuilderImpl extends UserDataHolderBase implements PsiBuilder {
   private int myLexemeCount = 0;
   private boolean myTokenTypeChecked;
   private ITokenTypeRemapper myRemapper;
+  private WhitespaceSkippedCallback myWhispaceSkippedCallback;
+
 
   private ASTNode myOriginalTree = null;
   private MyTreeStructure myParentLightTree = null;
@@ -610,6 +612,23 @@ public class PsiBuilderImpl extends UserDataHolderBase implements PsiBuilder {
     myRemapper = remapper;
   }
 
+  @Override
+  public void remapCurrentToken(IElementType type) {
+    myLexTypes[myCurrentLexeme] = type;
+  }
+
+  @Nullable
+  @Override
+  public IElementType lookAhead(int steps) {
+    if (steps + myCurrentLexeme >= myLexemeCount) return null;
+    return myLexTypes[myCurrentLexeme + steps];
+  }
+
+  @Override
+  public void setWhitespaceSkippedCallback(WhitespaceSkippedCallback callback) {
+    myWhispaceSkippedCallback = callback;
+  }
+
   public void advanceLexer() {
     if (eof()) return;
 
@@ -621,7 +640,16 @@ public class PsiBuilderImpl extends UserDataHolderBase implements PsiBuilder {
   }
 
   private void skipWhitespace() {
-    while (myCurrentLexeme < myLexemeCount && whitespaceOrComment(myLexTypes[myCurrentLexeme])) myCurrentLexeme++;
+    while (myCurrentLexeme < myLexemeCount && whitespaceOrComment(myLexTypes[myCurrentLexeme])) {
+      onSkip(myLexTypes[myCurrentLexeme], myLexStarts[myCurrentLexeme], myCurrentLexeme + 1 < myLexemeCount ? myLexStarts[myCurrentLexeme + 1] : myText.length());
+      myCurrentLexeme++;
+    }
+  }
+
+  private void onSkip(IElementType type, int start, int end) {
+    if (myWhispaceSkippedCallback != null) {
+      myWhispaceSkippedCallback.onSkip(type, start, end);
+    }
   }
 
   public int getCurrentOffset() {