code: public synchronized void put(String fileName, VersionedFile versionedFile) {
      cache.put(fileName, versionedFile.copy());
    }
docs: Stores a cached version of the AST.
  
  <p>Please treat this as superpackage-private for Soy internals.
  
  @param fileName The name of the file.
  @param versionedFile The compiled AST at the particular version. The node is defensively
  copied; the caller is free to modify it.