What remains to be done:

• port the tests from WIP: Add Mirage_job to wrap Bos actions #930 (and maybe add more?)
• update mirage-skeleton

Updated, now the only module using Bos is Functoria.Action. There are too much Action.run in the current code, but they are a bit hard to remove (as doing will propagate 'a Action.t a bit everywhere, especially inside 'a Cmdliner.Term.t where they become a pain to manipulate).

Current use of Action.run:

lib/functoria/app.ml:    build_and_execute ~state ?help_ppf ?err_ppf argv |> Action.run |> function
lib/functoria/app.ml:      run_configure_with_argv ~state Action.run Sys.argv c
lib/functoria/app.ml:    run () |> Action.run |> exit_err
lib/functoria/opam.ml:    match Action.run @@ find_git () with
lib/mirage/mirage_key.ml:    ( match Action.run @@ Action.run_cmd_out Bos.Cmd.(v "uname" % "-s") with
test/f0/f0.ml:    match Action.run @@ split_root () with
test/functoria/gen-1/test.ml:  match Action.run (test ()) with Ok () -> () | Error (`Msg e) -> failwith e
test/functoria/gen-2/test.ml:  match Action.run (test ()) with Ok () -> () | Error (`Msg e) -> failwith e
test/mirage/gen-1/test.ml:  match Functoria.Action.run (test ()) with

The one in functoria/opam.ml are filesystem access to guess the repository root ; and the one in mirage/mirage_key.ml is to find the kind of OS we are running on. I think that's ok to keep them like this for now on. The important ones are the one in functoria/app.ml where they are used in register and run_with_argv. We could expose similar functions which are interpreted instead to ease testing, I'll experiment with this next.

Tests have been added, but it seems that something is a bit off, as test/mirage/action/test.expected is truncated vs. https://github.com/mirage/mirage/pull/930/files#diff-7661350cdd5ae1288a23149c76a53107

I've just pushed a few tests for Functoria.Action. It should now have a good test coverage.

Still need to inspect the mirage test results before merging this, as they look a bit empty to me.

The goal of this PR is to track any operations on the system (like copy, open_file, etc.) ?

Yes the goal is to never use Bos directly. 'a Action.t actions can be introspected, so we can compute the set of generated files automatically. It's also makes the whole thing much easier to test (just print the trace instead of calling Bos) and it also allow to add a --dry-run command to list the commands before running them.

Pushed a new version, with more tests and a small fix on mirage-skeleton which should make Travis happt.

All green! I'll squash and merge here and in mirage-skeleton