versions for file type detectors + usage of them for file type index

platform/core-api/src/com/intellij/openapi/fileTypes/FileTypeRegistry.java

@@ -102,5 +102,7 @@ public abstract class FileTypeRegistry {
      */
     @Nullable
     FileType detect(@NotNull VirtualFile file, @NotNull ByteSequence firstBytes, @Nullable CharSequence firstCharsIfText);
+
+    int getVersion();
   }
 }

platform/indexing-impl/src/com/intellij/psi/search/FileTypeIndex.java

@@ -15,6 +15,7 @@
  */
 package com.intellij.psi.search;
 
+import com.intellij.openapi.extensions.Extensions;
 import com.intellij.openapi.fileTypes.FileType;
 import com.intellij.openapi.fileTypes.FileTypeRegistry;
 import com.intellij.openapi.util.Comparing;
@@ -87,6 +88,11 @@ public class FileTypeIndex extends ScalarIndexExtension<FileType>
     for (FileType type : types) {
       version += type.getName().hashCode();
     }
+
+    version *= 31;
+    for (FileTypeRegistry.FileTypeDetector detector : Extensions.getExtensions(FileTypeRegistry.FileTypeDetector.EP_NAME)) {
+      version += detector.getVersion();
+    }
     return version;
   }
 

plugins/groovy/src/org/jetbrains/plugins/groovy/GroovyHashBangFileTypeDetector.java

@@ -36,4 +36,9 @@ public class GroovyHashBangFileTypeDetector implements FileTypeRegistry.FileType
 
     return null;
   }
+
+  @Override
+  public int getVersion() {
+    return 1;
+  }
 }

python/src/com/jetbrains/python/PyFileTypeDetector.java

@@ -31,4 +31,9 @@ public class PyFileTypeDetector implements FileTypeRegistry.FileTypeDetector {
   public FileType detect(@NotNull VirtualFile file, @NotNull ByteSequence firstBytes, @Nullable CharSequence firstCharsIfText) {
     return FileUtil.isHashBangLine(firstCharsIfText, "python") ? PythonFileType.INSTANCE : null;
   }
+
+  @Override
+  public int getVersion() {
+    return 1;
+  }
 }