I completely agree that Rust ought to build in support for the error-chaining pattern. I think I'd still prefer to have a named type, but the standard library should provide a standard way to construct that type.

> 3. It's the other way around &str to String, having to call .to_string() everywhere. Make it implicit if the type expects a String while a &str is passed in.

You can't turn a reference like &str into an owned type like String without making a copy, and Rust doesn't do implicit copies (among many other reasons, because doing so would make it harder to notice code patterns that will lead to poor performance). So you'll always have to have some explicit indication that you want to make a copy.

In general, most functions should accept &str parameters rather than String, for exactly that reason; you should rarely run into functions that want a String. You can also use the "Cow" type if you want to support both owned and borrowed strings in the same structure.