bug#70794: 30.0.50; Add Rust compilation regex

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 06 May 2024 03:28:43 +0200
> From:  Ergus via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> Recently working with rust I have noticed that emacs does not recognizes
> the rust/cargo error patterns.
> 
> Considering that emacs has now the rust-ts-mode, it may worth adding
> the rust/cargo error patterns to compile when using that mode
> 
> In my system so far I have this:
> 
> ```
> (with-eval-after-load 'rust-ts-mode
>   (with-eval-after-load 'compile
>     (add-to-list
>      'compilation-error-regexp-alist-alist
>      `(cargo
>        "\\(?:\\(?4:error\\)\\|\\(?5:warning\\)\\):[^\0]+?--> \\(?1:[^:]+\\):\\(?2:[[:digit:]]+\\):\\(?3:[[:digit:]]+\\)"
>        1 2 3 (5)
>        nil
>        (5 compilation-warning-face)
>        (4 compilation-error-face)))
> 
>     (add-to-list 'compilation-error-regexp-alist 'cargo)))
> 
> ```
> 
> Maybe a more frequent rust user has a more general regex to
> recommend. But this one works for me.
> 
> WDYT?

Thanks, but could you please also send the examples of Rust messages,
because we need to add them to etc/compilation.txt?