`map_err` does not need to be type-directed; you can use an arbitrary function or closure. An enum variant can be used as a function mapping from the variant type to the error type, but we can do any arbitrary transformation:

    .map_err(|e| format!("Failed to read file: {e}")?;

But the "idiomatic Go" way of doing things sounds a lot closer to anyhow in Rust, which provides convenience utilities for dealing with type-erased errors:

    use anyhow::{Result, Context};

    fn foo() -> Result<()> {
        let data = std::fs::read("/some/file").context("Failed to read file")?;
        // ...
    }