color-spantrace: print_source_if_avail: can't extract source if working dir is crate in workspace

[d4h0]

Hi,

I'm debugging my PR for color_eyre at the moment. For some reason, the source code lines were not printed out.

The reason was, that I'm using a workspace and that tracing_core::metadata::Metadata contains a file path relative to the workspace, not my current working directory.

So I'm in "$workspace/color_eyre" and execute a test.

This line is then executed because filename is "color-spantrace/tests/color_schemes.rs" – which is relative to the workspace, not my current working directory:

        // `filename` can't be found, because it's relative to the workspace
        let file = match File::open(filename) {
            Ok(file) => file,
            // return without printing the source:
            Err(ref e) if e.kind() == ErrorKind::NotFound => return Ok(()),
            e @ Err(_) => e.unwrap(),
        };

I believe this is only a problem for people who work on color_spantrace, and not for end-users who install color_spantrace via cargo (but I'm not 100% sure).

I'm reporting this in case there is an easy workaround (I can't see one), or in case this could lead to problems for end-users.

Feel free, to close this if you don't think this is a problem.

Maybe a note in the README for people who want to work on color_spantrace would make sense?

[d4h0]

Basically, normally you'd get the following:

  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ SPANTRACE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  
   0: styles::get_error with msg="test"
      at tests/styles.rs:13
        11 │ 
        12 │ #[rustfmt::skip]
        13 > #[tracing::instrument]
        14 │ fn get_error(msg: &'static str) -> Report {
        15 │ 

Because of the bug I got:

  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ SPANTRACE ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
  
   0: styles::get_error with msg="test"
      at tests/styles.rs:13

[yaahc]

Aah yea, I have a PR that attempts to fix this but I never figured out the proper way to resolve the relative paths we should be searching in and ended up forgetting about the PR, I should really try to finish that one...

[d4h0]

I think Cargo should offer the root directory of the current base directory (the workspace or the standalone dir) as an environment variable, but it seems this doesn't exist.

Maybe OUT_DIR or CARGO_MANIFEST_DIR could be used to derive the right directory?