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Error message for question mark operator should message conversion #60917
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For what it's worth, the current output points at the question mark now:
error[E0277]: `?` couldn't convert the error to `Error2` --> src/main.rs:11:10 | 11 | foo()?; | ^ the trait `std::convert::From<Error1>` is not implemented for `Error2` | = note: required by `std::convert::From::from`Reacted by Sunjay VarmaThanks! That's a good start. I find that just pointing to it isn't enough because people don't even know that the question mark operator performs a conversion. The [edition guide] (https://doc.rust-lang.org/edition-guide/rust-2018/error-handling-and-panics/the-question-mark-operator-for-easier-error-handling.html) (a top result for looking up "rust question mark operator") doesn't even reference the From trait.
Reacted by Esteban Kuber
I've been working with a lot of people who are either new to Rust or new to its latest features (like the question mark operator) and I'm noticing a lot of confusion around a specific error message.
Suppose you have the following code:
This gives you the error:
However, if you look at the actual code, it isn't obvious where the
Fromtrait is even being used.The documentation for the
Fromtrait actually does mention this briefly, though most people I encounter don't go as far as looking that up. The error message is pretty daunting if you're new to the language.I propose that we add something to the error message when we see that they are using the question mark:
This conveys exactly where the
Fromtrait is being used and why they may be running into this issue. You certainly don't have to use this exact wording. Feel free to use whatever fits. :)