[RPC] Allow formatting while watch server is running

[ElectreAAS]

This PR is a second step towards implementing #11958, and is the 'big sister' of #12010.
Like its sister, this PR contains stolen code from Steve's #11900. 'Stolen' code has been merged on main

It is currently in draft mode It is now ready for review! The mechanism for promotion is now sound :)

[shonfeder]

Hi! Could you provide some context by explaining what you find sketchy about the enabling?

[ElectreAAS]

Not sold on the idea of having the target be determined by a string parse like this, isn't there a cleaner way?

[Alizter]

We don't have access to any of the information of the build targets here since interpretation comes at a later point. If you are uncomfortable by the string, you could use

      let target =
        Sexp.(List [ Atom "alias_rec"; Atom "fmt" ])
        |> Sexp.to_string
        |> server.parse_build_arg
      in

but ultimately it's the same thing.

[rgrinberg]

Not sold on the idea of having the target be determined by a string parse like this, isn't there a cleaner way?

The cleaner way is to introduce a new build request that offers a stable type for targets.

You are right to be suspicious of this since the way the server is parsing this string depends is dependent on the dune lang. This makes RPC more fragile than needed.

[ElectreAAS]

Dune_lang.Dep_conf.Alias_rec (Dune_lang.String_with_vars.make_text Loc.none "fmt") is how it's now done. If there is another way about doing this then I don't know what it is

[ElectreAAS]

Pet peeve, but this should be sorted. I added dune_lang as I pull it up as dependency in server.ml

[shonfeder]

@ElectreAAS Can this be merged now?

[ElectreAAS]

@ElectreAAS Can this be merged now?

No! There is a problem with the cache, and the --preview situation isn't yet under control

Now, yes it is!