test: Repro 'dune fmt' crash in presence of Nix result

[Julow]

Reproduction case for a crash when using dune fmt.
Perhaps formatting shouldn't follow symlinks ? Also, dune build doesn't seem to have any problem with that, perhaps because the linked directory doesn't contain a dune file.
Perhaps symlinked directories should be considered vendored_dirs automatically ?

[anmonteiro]

I have seen this before and it can be a bit puzzling.

IMO the issue here isn't that dune is following symlinks, but rather that the files in the nix store /nix/store/... have pretty locked-down permissions as one would expect.

I'm not saying that dune is perfect, just trying to point out the actual cause. There might be work to be done in dune itself.

[Julow]

Is here a case where we want the files in the symlinked directory be formatted ?

[Leonidas-from-XIV]

Thanks for the repro case; I've posted some comments.

As to how to deal with projects like this, if we can't find the proper solution I would suggest adding it to the dev-meeting agenda to discuss.

[Leonidas-from-XIV]

Could you filter the output a bit so it is more reproducible? The locations in the stacktrace are probably going to change over time. A simple grep EACCES is probably sufficient to show there's a very specific error that happens.

[Julow]

I hopted to remove the output and rely on the exit status.