Use error from stderr if stdout is empty

[adumbidiot]

I believe this fixes #24.

[fenhl]

Indeed it does.

[jyn514]

Thanks for the PR! It would be really nice to have tests for this behavior, but this change is obviously correct so I'll go ahead and merge for now :) let me know if you're interested in following up.

[adumbidiot]

Honestly, I wasn't sure why stdout is involved at all when it seems the stderr always has the error (from my testing). However, I assumed that this isn't always the case, as the person who wrote this block probably got an error from the stdout since thats the way they wrote that. Also, I am not sure how I would write a test for this. Would we somehow create a project with an error for sweep to find?

[jyn514]

Would we somehow create a project with an error for sweep to find?

That was my idea, yeah :) You should be able to reproduce it consistently by adding a custom rustc shell script in PATH that always gives an error.

It looks like cargo-sweep only has unit tests currently, not integration tests, so we'd need to set those up - in deadlinks I use assert_cmd which works pretty well without much boilerplate: https://github.com/deadlinks/cargo-deadlinks/blob/73de1dfcc24c6dcb2743505c176ff96aff9ca28d/tests/broken_links.rs#L8-L28
Let me know if that sounds like a hassle and I can add this first test, and hopefully it will be easier to add more in the future :)

[adumbidiot]

Sorry, not sure if I have the time for that in the next few weeks. I'll try to implement that though if this test is still missing when I get some free time.

[fenhl]

Could we get a crates.io release with this fix please?