dune-pkg: Better error messages on extract fail

[H-ANSEN]

This pull request is in reference to and would close #11549 (as well as possibly other related issues) by capturing the output of commands such as tar, gzip, and unzip when dune attempts to install a package and reporting a corresponding error message. The following is an example of the tool tar encountering a corrupted file:

File "dune.lock/foo.pkg", line 6, characters 3-136:
6 |    file:///DIR_NOT_INCLUDED_FOR_BREVITY/corrupted.tar)))
       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Error: failed to extract 'corrupted.tar'
  Reason: tar failed with non-zero exit code '2' and output:
  - /usr/bin/tar: This does not look like a tar archive
  - /usr/bin/tar: Exiting with failure status due to previous errors

One note, relating to the original issue was that I was unable to test behavior when a corresponding tool did not exist on the system. If any guidance on how to check this case could be provided I would be more than willing to add additional handling and tests for this case :)

[H-ANSEN]

It appears that tar on MacOS exit's with a different exit code and error message than on Linux! Is there any way to isolate test cases/expected output to MacOS or Linux? Or should I just preprocess the output with sed?

[gridbugs]

It appears that tar on MacOS exit's with a different exit code and error message than on Linux! Is there any way to isolate test cases/expected output to MacOS or Linux? Or should I just preprocess the output with sed?

Thanks for the patch! Indeed different tar implementations will have different error messages, and also the location of tar on different systems will differ; there's no guarantee it will be at /usr/bin/tar. Conventionally in dune tests we do jest process the output with sed and friends to make it as consistent across platforms as possible.

[gridbugs]

Looks like this also solves #11550.

[Leonidas-from-XIV]

Is there any way to isolate test cases/expected output to MacOS or Linux?

Yes, you can enable and disable tests depending on the platform they're running on: https://github.com/ocaml/dune/blob/main/test/blackbox-tests/test-cases/pkg/dune#L22-L26 but for cases where the errors are different I agree with @gridbugs that some postprocessing (or a fake injected tar which is consistent) is the better solution as that prevents the test evolving into two divergent tests.

[H-ANSEN]

This should now be passing, the issue on ubuntu-latest seems to be unrelated.

[Leonidas-from-XIV]

Looks pretty good. The failing test is being flaky sometimes and fixes itself upon rerunning usually. I've added some comments of things to look into but overall I think this is a good approach.