Restore compatibility with Alcotest 1.4.0

[craigfe]

The Alcotest 1.4.0 release adds optional arguments to Alcotest.fail. Eta-expansion is necessary to use this function with the continuation printers.

[dinosaure]

LGTM

[hannesm]

Thanks @craigfe. I'm curious seeing the amount of failures in ocaml/opam-repository#18509 (and the API change in alcotest 1.4.0) whether:

• it should be 2.0.0 (for the believers of semantic versioning)
• the 1.4.0 release could be revised to avoid this API break?

But of course I'm as well fine to merge this as is once alcotest 1.4.0 is merged into opam-repository as is. :)

[craigfe]

Hi @hannesm.

The rev-dep failures in this release were all due to this line of code (Fmt.kstrf Alcotest.fail), which seems to have propagated throughout the Mirage codebases. (This surprised me a bit, since Alcotest.failf has been available for a while.) If I'd been aware, I'd probably have held back this change for a major release.

Now that I've gotten this far it seems most efficient for me to make PRs to fix the few packages that still have this line in their dev versions, but I can still drop the Alcotest.fail change if you have a strong preference. (I'd rather not bump to 2.0.0 just for this, since I'd like to leave room for potential major breaking changes to be given more weight in the versioning scheme.)

[hannesm]

@craigfe as said, I'm fine with pushing 1.4.0 as is, and merging this (and similar PRs) across the mirage repositories.