Added prefix change listener for tracking state after char typing

platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/LookupImpl.java

@@ -67,8 +67,10 @@ import javax.swing.event.ListSelectionListener;
 import java.awt.*;
 import java.awt.event.KeyEvent;
 import java.awt.event.MouseEvent;
-import java.util.*;
+import java.util.Collection;
+import java.util.HashMap;
 import java.util.List;
+import java.util.Map;
 
 public class LookupImpl extends LightweightHint implements LookupEx, Disposable, WeighingContext {
   private static final Logger LOG = Logger.getInstance("#com.intellij.codeInsight.lookup.impl.LookupImpl");
@@ -102,6 +104,7 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable,
   final LookupCellRenderer myCellRenderer;
 
   private final List<LookupListener> myListeners = ContainerUtil.createLockFreeCopyOnWriteList();
+  private PrefixChangeListener myPrefixChangeListener = new PrefixChangeListener.Adapter() {};
 
   private long myStampShown = 0;
   private boolean myShown = false;
@@ -307,6 +310,7 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable,
     requestResize();
     refreshUi(false, true);
     ensureSelectionVisible(true);
+    myPrefixChangeListener.afterAppend(c);
   }
 
   public void setStartCompletionWhenNothingMatches(boolean startCompletionWhenNothingMatches) {
@@ -1158,6 +1162,10 @@ public class LookupImpl extends LightweightHint implements LookupEx, Disposable,
     }
   }
 
+  public void setPrefixChangeListener(PrefixChangeListener listener) {
+    myPrefixChangeListener = listener;
+  }
+
   public enum FocusDegree { FOCUSED, SEMI_FOCUSED, UNFOCUSED }
 
 }

platform/lang-impl/src/com/intellij/codeInsight/lookup/impl/PrefixChangeListener.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2000-2015 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 com.intellij.codeInsight.lookup.impl;
+
+public interface PrefixChangeListener {
+
+    void afterAppend(char c);
+    
+    abstract class Adapter implements PrefixChangeListener {
+        @Override
+        public void afterAppend(char c) {}
+    }
+}