Support the "word_size" variable in "enabled_if".

[rlepigre]

Desired Behavior

The variables accessible as part of the enabled_if field of the library stanza (and probably others like executable) only support a limited range of variables that does not include word_size. I think it would make sense to include it so that one can restrict the compilation of a library to 64-bit architectures, which makes sense if you rely, e.g., on an int counters not overflowing, but you do not want to pay the extra cost of using an Int64.t.

[Alizter]

I've started a draft, but I will have to do some more detailed testing later. We don't have a variable for word_size currently, so that would have to be added first.

[hhugo]

There exists Int63 for this very use case (see https://discuss.ocaml.org/t/advantage-of-int63-compared-to-int64/7465)

[rlepigre]

There exists Int63 for this very use case (see https://discuss.ocaml.org/t/advantage-of-int63-compared-to-int64/7465)

Good to know, thanks. In the use case I had in mind that would not work though, because it is not really an option to pull in a new dependency. It's be great if a type like this was in the OCaml standard library.

[hhugo]

There exists Int63 for this very use case (see https://discuss.ocaml.org/t/advantage-of-int63-compared-to-int64/7465)

Good to know, thanks. In the use case I had in mind that would not work though, because it is not really an option to pull in a new dependency. It's be great if a type like this was in the OCaml standard library.

It also exists in https://opam.ocaml.org/packages/optint/

[hhugo]

The doc mentions the arch_sixtyfour variable which seems to fit your usecase.
Note that word_size/int_size is a property of the runtime when building a bytecode executable because one could build a bytecode on 64bit arch and run it on a 32bit one.

[rlepigre]

I see, makes sense. However, arch_sixtyfour is not supported either in enabled_if.

File "perf/dune", line 7, characters 18-35:
7 |  (enabled_if (and %{arch_sixtyfour} (= %{system} linux))))
                      ^^^^^^^^^^^^^^^^^
Error: Only architecture, system, model, os_type, ccomp_type, profile,
ocaml_version and context_name variables are allowed in this 'enabled_if'
field. If you think that arch_sixtyfour should also be allowed, please file
an issue about it.

[hhugo]

cc @Alizter

[Alizter]

Yes, we could probably add this in. I'll draft somrthing later on.

[Alizter]

OK here is the PR #8023