diff --git a/java/java-analysis-impl/src/com/intellij/openapi/roots/JavaProjectRootsUtil.java b/java/java-analysis-impl/src/com/intellij/openapi/roots/JavaProjectRootsUtil.java
index 6adf0c47ce9d..9f8b331d8d92 100644
--- a/java/java-analysis-impl/src/com/intellij/openapi/roots/JavaProjectRootsUtil.java
+++ b/java/java-analysis-impl/src/com/intellij/openapi/roots/JavaProjectRootsUtil.java
@@ -18,6 +18,7 @@ package com.intellij.openapi.roots;
 import com.intellij.openapi.module.Module;
 import com.intellij.openapi.module.ModuleManager;
 import com.intellij.openapi.project.Project;
+import com.intellij.openapi.vfs.NonPhysicalFileSystem;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.psi.PsiCodeFragment;
 import com.intellij.psi.PsiFile;
@@ -42,6 +43,7 @@ public class JavaProjectRootsUtil {
     if (psiFile instanceof PsiCodeFragment) return false;
     final VirtualFile file = psiFile.getVirtualFile();
     if (file == null) return false;
+    if (file.getFileSystem() instanceof NonPhysicalFileSystem) return false;
     final ProjectFileIndex projectFileIndex = ProjectRootManager.getInstance(psiFile.getProject()).getFileIndex();
     return !projectFileIndex.isUnderSourceRootOfType(file, JavaModuleSourceRootTypes.SOURCES) && !projectFileIndex.isInLibrarySource(file)
            && !projectFileIndex.isInLibraryClasses(file);
diff --git a/platform/diff-impl/src/com/intellij/diff/DiffContentFactoryImpl.java b/platform/diff-impl/src/com/intellij/diff/DiffContentFactoryImpl.java
index c03b2fdbf4c9..29da3e6002b5 100644
--- a/platform/diff-impl/src/com/intellij/diff/DiffContentFactoryImpl.java
+++ b/platform/diff-impl/src/com/intellij/diff/DiffContentFactoryImpl.java
@@ -423,10 +423,10 @@ public class DiffContentFactoryImpl extends DiffContentFactoryEx {
                                             @NotNull String fileName,
                                             boolean readOnly) {
     return ReadAction.compute(() -> {
-      LightVirtualFile file = new LightVirtualFile(fileName, DiffPsiFileType.INSTANCE, content);
+      LightVirtualFile file = new LightVirtualFile(fileName, fileType, content);
       file.setWritable(!readOnly);
 
-      file.putUserData(DiffPsiFileType.ORIGINAL_FILE_TYPE_KEY, fileType);
+      file.putUserData(DiffPsiFileSupport.KEY, true);
 
       Document document = FileDocumentManager.getInstance().getDocument(file);
       if (document == null) return null;
diff --git a/platform/diff-impl/src/com/intellij/diff/contents/DiffPsiFileType.java b/platform/diff-impl/src/com/intellij/diff/contents/DiffPsiFileSupport.java
similarity index 55%
rename from platform/diff-impl/src/com/intellij/diff/contents/DiffPsiFileType.java
rename to platform/diff-impl/src/com/intellij/diff/contents/DiffPsiFileSupport.java
index c5c6b29f14eb..28f83801977e 100644
--- a/platform/diff-impl/src/com/intellij/diff/contents/DiffPsiFileType.java
+++ b/platform/diff-impl/src/com/intellij/diff/contents/DiffPsiFileSupport.java
@@ -21,81 +21,16 @@ import com.intellij.codeInsight.daemon.impl.IntentionActionFilter;
 import com.intellij.codeInsight.daemon.impl.analysis.DefaultHighlightingSettingProvider;
 import com.intellij.codeInsight.daemon.impl.analysis.FileHighlightingSetting;
 import com.intellij.codeInsight.intention.IntentionAction;
-import com.intellij.icons.AllIcons;
-import com.intellij.lang.Language;
 import com.intellij.lang.annotation.HighlightSeverity;
-import com.intellij.openapi.fileTypes.*;
-import com.intellij.openapi.fileTypes.ex.FileTypeIdentifiableByVirtualFile;
 import com.intellij.openapi.project.Project;
 import com.intellij.openapi.util.Key;
 import com.intellij.openapi.vfs.VirtualFile;
-import com.intellij.psi.LanguageSubstitutor;
 import com.intellij.psi.PsiFile;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
-import javax.swing.*;
-
-public class DiffPsiFileType extends LanguageFileType implements FileTypeIdentifiableByVirtualFile, PeripheralFileType {
-  public static final Key<FileType> ORIGINAL_FILE_TYPE_KEY = Key.create("Diff.DiffPsiFileType.OriginalFileTypeKey");
-  public static final LanguageFileType INSTANCE = new DiffPsiFileType();
-
-  DiffPsiFileType() {
-    super(PlainTextLanguage.INSTANCE);
-  }
-
-  @Override
-  public boolean isMyFileType(@NotNull VirtualFile file) {
-    return isDiffFile(file);
-  }
-
-  @NotNull
-  @Override
-  public String getName() {
-    return "Diff";
-  }
-
-  @NotNull
-  @Override
-  public String getDescription() {
-    return "Diff";
-  }
-
-  @NotNull
-  @Override
-  public String getDefaultExtension() {
-    return "";
-  }
-
-  @Nullable
-  @Override
-  public Icon getIcon() {
-    return AllIcons.Diff.Diff;
-  }
-
-  @Override
-  public boolean isReadOnly() {
-    return true;
-  }
-
-  @Nullable
-  @Override
-  public String getCharset(@NotNull VirtualFile file, @NotNull byte[] content) {
-    return null;
-  }
-
-
-  public static class Substitutor extends LanguageSubstitutor {
-    @Nullable
-    @Override
-    public Language getLanguage(@NotNull VirtualFile file, @NotNull Project project) {
-      FileType originalType = getOriginalFileType(file);
-      if (originalType instanceof LanguageFileType) {
-        return ((LanguageFileType)originalType).getLanguage();
-      }
-      return null;
-    }
-  }
+public class DiffPsiFileSupport {
+  public static final Key<Boolean> KEY = Key.create("Diff.DiffPsiFileSupport");
 
   public static class HighlightFilter implements HighlightInfoFilter {
     @Override
@@ -128,12 +63,6 @@ public class DiffPsiFileType extends LanguageFileType implements FileTypeIdentif
   }
 
   private static boolean isDiffFile(@Nullable VirtualFile file) {
-    return file != null && getOriginalFileType(file) != null;
-  }
-
-  @Nullable
-  private static FileType getOriginalFileType(@NotNull VirtualFile file) {
-    FileType fileType = file.getUserData(ORIGINAL_FILE_TYPE_KEY);
-    return fileType instanceof DiffPsiFileType ? null : fileType;
+    return file != null && file.getUserData(KEY) == Boolean.TRUE;
   }
 }
diff --git a/platform/platform-resources/src/META-INF/PlatformExtensions.xml b/platform/platform-resources/src/META-INF/PlatformExtensions.xml
index 45fd1312c53c..8f0116eb6614 100644
--- a/platform/platform-resources/src/META-INF/PlatformExtensions.xml
+++ b/platform/platform-resources/src/META-INF/PlatformExtensions.xml
@@ -107,11 +107,10 @@
     <colorAndFontPanelFactory implementation="com.intellij.openapi.diff.impl.settings.DiffColorsPageFactory"/>
     <colorAndFontDescriptorProvider implementation="com.intellij.openapi.diff.impl.settings.DiffColorsPageFactory"/>
 
-    <lang.substitutor language="TEXT" implementationClass="com.intellij.diff.contents.DiffPsiFileType$Substitutor" order="first"/>
-    <daemon.highlightInfoFilter implementation="com.intellij.diff.contents.DiffPsiFileType$HighlightFilter"/>
-    <daemon.intentionActionFilter implementation="com.intellij.diff.contents.DiffPsiFileType$IntentionFilter"/>
+    <daemon.highlightInfoFilter implementation="com.intellij.diff.contents.DiffPsiFileSupport$HighlightFilter"/>
+    <daemon.intentionActionFilter implementation="com.intellij.diff.contents.DiffPsiFileSupport$IntentionFilter"/>
     <defaultHighlightingSettingProvider id="GeneratedSourcesHighlightingSettingProvider"
-                                        implementation="com.intellij.diff.contents.DiffPsiFileType$HighlightingSettingProvider"/>
+                                        implementation="com.intellij.diff.contents.DiffPsiFileSupport$HighlightingSettingProvider"/>
 
     <applicationService serviceInterface="com.intellij.ui.SystemNotifications"
                         serviceImplementation="com.intellij.ui.SystemNotificationsImpl"/>