unison needs one of bcpierce00/unison#480 or bcpierce00/unison#481. See also bcpierce00/unison#482.

For coccinelle, I believe the compile error seen here:

File "stdcompat__arg_s.mli", lines 3-17, characters 0-38:
 3 | type spec = Arg.spec =
 4 |   | Unit of (unit -> unit) 
 5 |   | Bool of (bool -> unit) 
 6 |   | Set of bool ref 
 7 |   | Clear of bool ref 
...
14 |   | Tuple of spec list 
15 |   | Symbol of string list * (string -> unit) 
16 |   | Rest of (string -> unit) 
17 |   | Expand of (string -> string array).
Error: This variant or record definition does not match that of type Arg.spec
       Constructors number 14 have different names, Rest_all and Expand.

is being addressed upstream in coccinelle/coccinelle@3dc5d02
CC @thierry-martinez

coccinelle/coccinelle@3dc5d02 looks too big to include as a patch. (I'm going to guess it's also not going to apply to the release tarball.)

We may have to wait for a new version of Coccinelle before upgrading to Ocaml 4.12.

I think that installing stdcompat before coccinelle should solve the problem. I tried to propose a formula here: carlocab#1 but I am not used to homebrew...

Thanks. I don't think we can add ocaml-stdcompat to homebrew/core, as CI is going to complain that your repo has too few watchers/stars/forks. I'd be happy to add it to homebrew/core when that changes though.

In the meantime, I think we can install ocaml-stdcompat as a bootstrap resource during the build. However, how do we get opam and make to find it? (It'll be installed in a non-standard location.) Is it enough to add its bin to PATH, or is it something more involved?

I just tried installing ocaml-stdcompat locally, and it seems it's purely a library. I'm actually not super familiar with ocaml, so a hint on how to help opam/make find it in a non-standard location would be appreciated.

unison (not a release yet though) should now build with ocaml 4.12, and does CI with it. No fixed timetable but we are heading for a release soonish with this - maybe within a month.

For the hyperkit failure feel free to cherry-pick my fix I made for the previous PR bumping the OCaml version (closed without merging since then): chenrui333#5

Thanks for the updates and suggestions, @gdt and @kit-ty-kate.

Hyperkit is fixed in #72028 but not merged because it's not straightforward to test the build in Homebrew CI.

The only thing blocking this PR is my difficulty here: #71942 (comment)

If someone could tell me how I can use ocaml-stdcompat in a temporary install whose path I can provide, I can probably sort out the rest of this PR.

The only thing blocking this PR is my difficulty here: #71942 (comment)

If someone could tell me how I can use ocaml-stdcompat in a temporary install whose path I can provide, I can probably sort out the rest of this PR.

export OCAMLPATH=<your-path> should be enough (I've never had to use it but according to the doc it should be sufficient http://projects.camlcity.org/projects/dl/findlib-1.9.1/doc/ref-html/r865.html)

Thanks, @kit-ty-kate. I've given that a try in e72ce7a3311843db88d669dfee03e6326ee8fd6c.

Unless there are surprises on the Catalina and Big Sur nodes, this should be good to go. Failures on ARM Big Sur and Mojave are expected / pre-existing.

Thanks for all the help, @rvantonder, @thierry-martinez, @gdt, and @kit-ty-kate.

@carlocab has triggered a merge.