code: public static LetContentNode forVariable(
        int id,
        SourceLocation sourceLocation,
        String varName,
        SourceLocation varNameLocation,
        @Nullable SanitizedContentKind contentKind) {
      LetContentNode node =
          new LetContentNode(id, sourceLocation, varName, varNameLocation, contentKind);
      SoyType type =
          (contentKind != null)
              ? SanitizedType.getTypeForContentKind(contentKind)
              : StringType.getInstance();
      node.getVar().setType(type);
      return node;
    }
docs: Creates a LetContentNode for a compiler-generated variable. Use this in passes that rewrite the
  tree and introduce local temporary variables.