fix openbsd build

[xguerin]

No description provided.

[let-def]

Hi. Thanks for the patch.

In the light of #658, maybe it is better to find a more robust way to generate the socket path.
So I prefer to wait a bit and if we come up with a nicer solution, check that it doesn't break on OpenBSD before merging (Merlin 3 hasn't been released yet anyway).

[xguerin]

Ok, thanks. Since I am working on OpenBSD I'll be glad to take care of the testing if needed.

[let-def]

xguerin: can you try to rebase on current master? If it works, I will happily merge your PR. Thanks.

[xguerin]

Done. However, recent versions of merlin 3.0 are behaving strangely on OpenBSD. I am getting the following error when running ocamlmerlin:

execvp(ocamlmerlin-server): No such file or directory
merlin path: /home/xrg/merlin/ocamlmerlin-server
socket path: /tmp/<not computed yet>

I have not taken an in-depth look at what may be the source of the problem (ocamlmerlin-server is in my PATH). If I find something I'll let you know.

[let-def]

I was able to run your patched version on OpenBSD (6.1) without problem, so the problem must come from a difference in your setup. I tried with vim.
Are you using emacs?

[xguerin]

How do you call ocamlmerlin ? If I call it with its full path, it indeed works. If I call it with just ocamlmerlin, it fails.

It seems that realpath in ocamlmerlin.c:378 expands ocamlmerlin (argv0) into $PWD/ocamlmerlin, therefore skipping the search_in_path call. Removing line 378 fixes it for me.

It looks like the culprit may be w0rp/ale, which calls ocamlmerlin without its full path.

However, I don't really see the point of calling realpath above. I'm also quite flabbergasted that it would work out of the box on your OpenBSD installation. AFAICT, that call is not biased by any outside environment.

[let-def]

I see. My .vimrc for merlin development might workaround the issue.

The purpose of realpath is to follow symbolic links, but this approach is fragile, I have to think about something more robust for finding ocamlmerlin-server from ocamlmerlin.

[xguerin]

What about checking realpath only when argv0 is actually a path, i.e. skipping it when argv0 = "ocamlmerlin" ? That should cover pretty much all corner cases.

EDIT I apologize for being so dense, but although I get the reason why you want to use realpath, I am still not quite sure about that particular check on line 377:

if (realpath(argv0, merlin_path) == NULL)

From the OpenBSD MAN:

All but the last component of pathname must exist when realpath() is called.

Which differs apparently from the Linux version where all components must exist, period. However, since realpath is called on argv0, which for all intent and purpose is always going to be valid (otherwise the shell could not have run it), the return result of realpath is unlikely to be NULL.

My understanding is that you want to check whether or not a the binary was called using a path so you can either use that path (if it exists) to run ocamlmerlin-server or search PATH to find the proper location.

If my interpretation is correct, I gave it a shot here: #667.