bug#70794: 30.0.50; Add Rust compilation regex

[Ergus]

On Sat, May 11, 2024 at 11:51:04AM GMT, Eli Zaretskii wrote:
> > 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?

Hi Eli:

Typically they look like this:

```
error[E0425]: cannot find function `ruun` in module `broot::cli`
  --> src/main.rs:6:23
   |
6  |     match broot::cli::ruun() {
   |                       ^^^^ help: a function with a similar name exists: 
`run`
   |
  ::: /tmp/broot/src/cli/mod.rs:49:1
   |
49 | pub fn run() -> Result<Option<Launchable>, ProgramError> {
   | -------------------------------------------------------- similarly
   named function `run` defined here
```

or

```
error: cannot find macro `deebug` in this scope
   --> src/main.rs:5:5
    |
5   |     deebug!("env::args(): {:#?}", 
std::env::args().collect::<Vec<String>>());
    |     ^^^^^^ help: a macro with a similar name exists: `debug`
    |
   ::: 
/home/ergo/.cargo/registry/src/index.crates.io-6f17d22bba15001f/log-0.4.21/src/macros.rs:154:1
    |
154 | macro_rules! debug {
    | ------------------ similarly named macro `debug` defined here
```

```
warning: crate-level attribute should be an inner attribute: add an exclamation 
mark: `#![foo]`
 --> src/main.rs:3:1
  |
3 | #[feature(proc_macro_diagnostic)]
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_attributes)]` on by default
```

Two details:

1. As you can see the [] is optional
2. The path is always relative to project's root