3 files changed, 20 insertions, 7 deletions
diff --git a/platform/core-impl/src/com/intellij/psi/impl/source/tree/CompositeElement.java b/platform/core-impl/src/com/intellij/psi/impl/source/tree/CompositeElement.java
index f00c15220d57..c73d0bd485ce 100644
--- a/platform/core-impl/src/com/intellij/psi/impl/source/tree/CompositeElement.java
+++ b/platform/core-impl/src/com/intellij/psi/impl/source/tree/CompositeElement.java
@@ -771,8 +771,7 @@ public class CompositeElement extends TreeElement {
   }
 
   @Override
-  @Nullable
-  public <T extends PsiElement> T getPsi(Class<T> clazz) {
+  public <T extends PsiElement> T getPsi(@NotNull Class<T> clazz) {
     return LeafElement.getPsi(clazz, getPsi(), LOG);
   }
 
@@ -797,6 +796,10 @@ public class CompositeElement extends TreeElement {
     myWrapper = psi;
   }
 
+  protected void clearPsi() {
+    myWrapper = null;
+  }
+
   public final void rawAddChildren(@NotNull TreeElement first) {
     rawAddChildrenWithoutNotifications(first);
 
diff --git a/platform/core-impl/src/com/intellij/psi/impl/source/tree/FileElement.java b/platform/core-impl/src/com/intellij/psi/impl/source/tree/FileElement.java
index f025de75b820..76d5c421094d 100644
--- a/platform/core-impl/src/com/intellij/psi/impl/source/tree/FileElement.java
+++ b/platform/core-impl/src/com/intellij/psi/impl/source/tree/FileElement.java
@@ -19,6 +19,7 @@ package com.intellij.psi.impl.source.tree;
 import com.intellij.lang.ASTNode;
 import com.intellij.lang.FileASTNode;
 import com.intellij.openapi.util.Getter;
+import com.intellij.psi.PsiElement;
 import com.intellij.psi.impl.PsiManagerEx;
 import com.intellij.psi.impl.source.CharTableImpl;
 import com.intellij.psi.impl.source.PsiFileImpl;
@@ -28,6 +29,17 @@ import org.jetbrains.annotations.NotNull;
 
 public class FileElement extends LazyParseableElement implements FileASTNode, Getter<FileElement> {
   private volatile CharTable myCharTable = new CharTableImpl();
+  private volatile boolean myDetached;
+
+  @Override
+  protected PsiElement createPsiNoLock() {
+    return myDetached ? null : super.createPsiNoLock();
+  }
+
+  public void detachFromFile() {
+    myDetached = true;
+    clearPsi();
+  }
 
   @Override
   @NotNull
diff --git a/platform/core-impl/src/com/intellij/psi/impl/source/tree/LeafElement.java b/platform/core-impl/src/com/intellij/psi/impl/source/tree/LeafElement.java
index 929737177052..011cad8a8450 100644
--- a/platform/core-impl/src/com/intellij/psi/impl/source/tree/LeafElement.java
+++ b/platform/core-impl/src/com/intellij/psi/impl/source/tree/LeafElement.java
@@ -290,16 +290,14 @@ public abstract class LeafElement extends TreeElement {
   }
 
   @Override
-  @Nullable
-  public <T extends PsiElement> T getPsi(Class<T> clazz) {
+  public <T extends PsiElement> T getPsi(@NotNull Class<T> clazz) {
     return getPsi(clazz, getPsi(), LOG);
   }
 
-  @Nullable
-  static <T extends PsiElement> T getPsi(Class<T> clazz, PsiElement element, Logger log) {
+  static <T extends PsiElement> T getPsi(@NotNull Class<T> clazz, PsiElement element, Logger log) {
     log.assertTrue(clazz.isInstance(element), "unexpected psi class. expected: " + clazz
                                              + " got: " + (element == null ? null : element.getClass()));
+    //noinspection unchecked
     return (T)element;
   }
-
 }