Congratulations to the new release. For the curious who intend to install a flambda version of 4.12 and are surprised that ocaml-variants.4.12.0+flambda does not exist, from this thread the opam packaging has changed, The following opam invocation sets up a switch with a OCaml compiler that uses flambda:
$ opam sw create <my-switch-name> --packages=ocaml-variants.4.12.0+options,ocaml-options-only-flambda
There are more configuration options available, take a look at the output of opam search ocaml-option for all options. (I’ve not been involved with this development. I don’t quite understand why there is for each Y a ocaml-option-Y and a ocaml-options-only-Y.) I also have not figured out whether there’s a way to pass -O3 in the just created switch.
Maybe it is worth to embed such information in the very nicely styled OCaml manual (considering that opam got quite some traction over the years and is recommended for OCaml developers)?