Changing mutable borrow check error when it occurs in a loop

[ivanbakel]

I'm happy to write up a full RFC for this, but I'd prefer to float the idea and understand if more contextual messages are a good thing. Inspired by my own experience in rust-lang/rust#43437, the message for two mutable borrows doesn't account for the case of loops - producing an error message that looks strange and doesn't really communicate what the borrow checker is having a problem with.

I'd like to change it so that the formatted message is changed based on it occuring inside a loop, similar to the use of moved value error message, which specifies when the move occurs in a loop iteration.

The code is already written, in ivanbakel/rust@53fb2a5 .

[Mark-Simulacrum]

I think that a PR would be sufficient for this. In general, if we can detect a particular case accurately (and with little overhead for the non-erroring path) more specific error messages are greatly preferable.

[ivanbakel]

What do you mean by a PR - a RFC PR, or a PR directly to the rust-lang/rust repo?

[Mark-Simulacrum]

Sorry, a PR directly to rust-lang/rust.

[ivanbakel]

My PR was merged, so I'm closing this.