Match panics in compilation-mode

[luckysori]

Fixes #507.

If we encounter a panic when executing Rust code in compilation-mode, we now correctly highlight the location where the panic occurred.

For example:

thread 'main' panicked at src/main.rs:2:5:
explicit panic
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Here, src/main.rs:2:5 is highlighted. The developer is then able to execute compile-goto-error to jump to the correct spot in the code.

[zachlefevre]

I think you should use the rustc-compilation-location variable already in scope.
Something like this

(let ((re (concat "thread '[^']+' panicked at " rustc-compilation-location)))
    (cons re '(2 3 4 nil 1)))
    ```

[luckysori]

Thanks for the tip! I'll give it a go later.

[luckysori]

Done, you were right!

[luckysori]

I've added a test now, but I'm not sure why this is nil and not compilation-error. Maybe someone more comfortable with Elisp can assist me.

[zachlefevre]

I am not very familiar with elisp either, so I could be wrong.
Here's what I think is happening here:
compilation-error is set

(defvar compilation-error "error"
  "Stem of message to print when no matches are found.")

And so an expression like ("file6.rs" "132" "34" compilation-error "file6.rs:132:34") is equivalent to ("file6.rs" "132" "34" error "file6.rs:132:34")'

That translates to type expression from the compilation-error-regexp-alist help doc. I'm getting that from this paragraph:

Each elt has the form (REGEXP FILE [LINE COLUMN TYPE HYPERLINK
HIGHLIGHT...]).  If REGEXP matches, the FILE’th subexpression
gives the file name, and the LINE’th subexpression gives the line
number.  The COLUMN’th subexpression gives the column number on
that line.

The definition of our regex is

defvar rustc-panics-compilation-regexps
   (let ((re (concat "thread '[^']+' panicked at " rustc-compilation-location)))
     (cons re '(2 3 4 nil 1)))
   "Specifications for matching panics in rustc invocations.
See `compilation-error-regexp-alist' for help on their format.")

And so we're capturing the:
2nd capture group for the file name
3rd capture group for the line number,
4th capture group for the column number,
nil for the type
1st capture group for the hyperlink.

We don't have an error or warning in our error message, like the others do, to parse out for the type, so our type is nil.

[zachlefevre]

so I think nil is correct. That, or invent a new type like panic. I'm not really sure.

[zachlefevre]

@luckysori This looks ready for review to me. Do you mind running @rustbot review? from https://rustc-dev-guide.rust-lang.org/contributing.html#waiting-for-reviews ?

[luckysori]

@rustbot review

[rustbot]

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[luckysori]

Error: The feature shortcut is not enabled in this repository. To enable it add its section in the triagebot.toml in the root of the repository.

Please file an issue on GitHub at triagebot if there's a problem with this bot, or reach out on #t-infra on Zulip.

I guess it's not enabled on this repo, @zachlefevre.

[zachlefevre]

@psibi Do you mind reviewing this?

[psibi]

Thanks @zachlefevre for the review and @luckysori for the PR and the test case! I have confirmed that it works for me, merging this.