DomFileElement.createStableCopy should survive PsiFile invalidation (IDEA-185043)

(cherry picked from commit 7188958a)

xml/dom-impl/src/com/intellij/util/xml/impl/DomFileElementImpl.java

@@ -17,15 +17,16 @@ package com.intellij.util.xml.impl;
 
 import com.intellij.openapi.diagnostic.Logger;
 import com.intellij.openapi.module.Module;
-import com.intellij.openapi.module.ModuleUtil;
 import com.intellij.openapi.module.ModuleUtilCore;
-import com.intellij.openapi.util.Factory;
 import com.intellij.openapi.util.Key;
+import com.intellij.openapi.vfs.VirtualFile;
+import com.intellij.psi.PsiManager;
 import com.intellij.psi.search.GlobalSearchScope;
 import com.intellij.psi.xml.XmlDocument;
 import com.intellij.psi.xml.XmlElement;
 import com.intellij.psi.xml.XmlFile;
 import com.intellij.psi.xml.XmlTag;
+import com.intellij.util.ObjectUtils;
 import com.intellij.util.xml.*;
 import com.intellij.util.xml.reflect.*;
 import com.intellij.util.xml.stubs.FileStub;
@@ -286,7 +287,10 @@ public class DomFileElementImpl<T extends DomElement> implements DomFileElement<
 
   @Override
   public final <T extends DomElement> T createStableCopy() {
-    return myManager.createStableValue(() -> (T)myManager.getFileElement(myFile));
+    PsiManager psiManager = myFile.getManager();
+    VirtualFile vFile = myFile.getViewProvider().getVirtualFile();
+    //noinspection unchecked
+    return myManager.createStableValue(() -> (T)myManager.getFileElement(ObjectUtils.tryCast(psiManager.findFile(vFile), XmlFile.class)));
   }
 
   @Override

xml/dom-impl/src/com/intellij/util/xml/impl/DomManagerImpl.java

@@ -335,7 +335,7 @@ public final class DomManagerImpl extends DomManager {
 
   @Override
   @Nullable
-  public final <T extends DomElement> DomFileElementImpl<T> getFileElement(XmlFile file) {
+  public final <T extends DomElement> DomFileElementImpl<T> getFileElement(@Nullable XmlFile file) {
     if (file == null) return null;
     if (!(file.getFileType() instanceof DomSupportEnabled)) return null;
     final VirtualFile virtualFile = file.getVirtualFile();

xml/dom-tests/tests/com/intellij/util/xml/DomBasicsTest.java

@@ -15,11 +15,17 @@
  */
 package com.intellij.util.xml;
 
+import com.intellij.lang.xml.XMLLanguage;
 import com.intellij.mock.MockModule;
+import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.application.Result;
 import com.intellij.openapi.command.WriteCommandAction;
 import com.intellij.openapi.module.Module;
 import com.intellij.openapi.util.text.StringUtil;
+import com.intellij.openapi.vfs.VirtualFile;
+import com.intellij.psi.PsiFileFactory;
+import com.intellij.psi.impl.PsiManagerEx;
+import com.intellij.psi.impl.file.impl.FileManagerImpl;
 import com.intellij.psi.xml.XmlFile;
 import com.intellij.psi.xml.XmlTag;
 import com.intellij.util.IncorrectOperationException;
@@ -534,6 +540,22 @@ public class DomBasicsTest extends DomTestCase {
     assertTrue(copy.isValid());
   }
 
+  public void testStableCopySurvivesPsiFileInvalidation() {
+    XmlFile xmlFile = (XmlFile)PsiFileFactory.getInstance(getProject())
+      .createFileFromText(XMLLanguage.INSTANCE, "<a><child-element/><child-element/></a>");
+    VirtualFile file = xmlFile.getViewProvider().getVirtualFile();
+
+    getDomManager().registerFileDescription(new MockDomFileDescription<>(MyElement.class, "a", file), getTestRootDisposable());
+    
+    MyElement element = getDomManager().getFileElement(xmlFile, MyElement.class).getRootElement().getChildElements().get(1);
+    MyElement copy = element.createStableCopy();
+
+    ApplicationManager.getApplication().runWriteAction(() -> ((FileManagerImpl)PsiManagerEx.getInstanceEx(getProject()).getFileManager()).forceReload(file));
+    
+    assertFalse(element.isValid());
+    assertTrue(copy.isValid());
+  }
+
   @Implementation(Impl.class)
   public interface MyElement extends DomElement {
     GenericAttributeValue<String> getAttr();