The code contains a number of type annotations that can hopefully be removed in the future. Example: https://github.com/alvra/reqwest-file/blob/f6a996e06a2e6a1a0421eadabb82e33257402e2b/src/lib.rs#L868 This depends on the following issue: https://github.com/rust-lang/rust/issues/83687. Which, unfortunately, is closed.