Make MDX tests idempotent

[SGrondin]

At the moment, developing with dune runtest -w is not the most pleasant experience. The first test run will succeed, but the subsequent runs of many tests (fs.md, process.md, README.md) will fail with various Already_exists and Not_found errors.

This PR cleans up those leftover artifacts to ensure accurate test outcomes.

I first tried to do something more automatic, where it would detect the previous artifacts, so that we won't have to remember to invoke the cleanup function with the right paths, but the result was more brittle than this. I wanted to make sure it would work even if the test gets interrupted, so the cleanup has to happen before the test run, not after it. Please let me know if you can think of a better approach.

[SGrondin]

@talex5 thanks for the comments! I'll add rm_r to Path and make the changes.

[SGrondin]

@talex5 I realize now why I didn't think to put rm_r/rmtree into Path: because it needs to be able to empty directories recursively, and it can't do that very well if symbolic links are present because the Path module functions always follow the symbolic links. I can't use Path.unlink on a symbolic link, I have to use the blocking Unix.unlink in a thread.

But I fully agree that such a function needs to be part of Path, I've already had to implement it 3 times in 3 different codebases. I have a few questions first in order to finish this PR:

• Q1: Should I add the function to Path as part of this PR? I think yes, since it would keep things simple.
• Q2: Should I implement the function by calling Unix.unlink in a new systhread (for now until #607 is fixed) when removing symbolic links? Or should just forego adding anything to Path for now until #607 is fixed?
  • Q3: Wouldn't a Workpool be a clean way to implement a thread pool for blocking system calls? If so I would be interested in making the changes to Eio_posix
• Q4: the name. I personally prefer rm_r because rmtree doesn't follow OCaml's snake case convention. rm_tree sounds like an alias of the inexistent Tree.rm. To my eyes, rm_r looks more OCaml-y and there's no confusion about its meaning were I not familiar with Eio. Ruby uses rm_r as well. That said, I think rmtree is perfectly acceptable if you insist!

[talex5]

I realize now why I didn't think to put rm_r/rmtree into Path: because it needs to be able to empty directories recursively, and it can't do that very well if symbolic links are present because the Path module functions always follow the symbolic links.

Right, this is why we need #599 first. That can be merged once https://github.com/ocaml/opam-repository/pull/24292 is accepted into opam-repository.

I can't use Path.unlink on a symbolic link, I have to use the blocking Unix.unlink in a thread.

Are you sure? Path.unlink works for me.

Regarding the name, Lwt calls this delete_recursively https://github.com/ocsigen/lwt/blob/2eee2a1b9e386cc0eacf455a5a9356150f920edb/src/unix/lwt_io.mli#L550

Another option would be Path.unlink ~recursive:true.

[SGrondin]

I like delete_recursively a lot 👍 Dangerous/powerful functions deserve longer, unambiguous names.

If I recall correctly, Path.unlink is unable to remove a symbolic link if that link points to something outside of cwd. It's why I had to resort to Unix.unlink in this PR. It looked as if Path.unlink was designed to seamlessly see through symbolic links, but now I understand it might just be a bug that occurs when the link points to something outside cwd.

[SGrondin]

I just tested symlinks Path operations every way I could think of, and I can confirm that it all works as expected. My earlier confusion came from the fact that I was statting with Path.with_open_in path Eio.File.stat and that's absolutely going to follow the symlink!

[SGrondin]

I've just made several improvements based on the previous review. I'll complete development of this PR as soon as #599 is merged.

[talex5]

Stat support is now merged (as #620), so we can unpause this PR now!

[SGrondin]

Fantastic! I'll probably work on it this Saturday.

[SGrondin]

@talex5 Updated! See my comments on Element about kind and rmtree. If you do decide to make changes to those 2 functions I'll want to update this PR. If not, then consider this PR ready.

[SGrondin]

Once this is merged we need to start requesting changes on PRs adding tests without proper usage of the ~clear argument. It's pretty easy to tell just by reading the test.

[talex5]

Thanks!