Port to dune 2.0

[emillon]

This ports to (lang dune 2.0) and uses all niceties from the new dune lang.

• (with-accepted-exit-codes) & (with-stdin-from) (these replace all our uses of (system))
• long-form target inference thanks to @NathanReb (this means that we can use file names directly without having to declare (targets) and refer to them as %{targets}

Note that this bumps the minimum dune version to 2.0.0. This shouldn't be too much of a problem since very few packages have a < 2.0.0 constraint on opam-repository (and almost all of them have a fixed version - the compatibility is pretty good).

Let me know what you think.

[jberdine]

I would suggest to test carefully whether the behavior described in ocaml/dune#2958 affects tests, etc. here.

[gpetiot]

I think it's worth adding a line in the changelog that the required dune version is now >= 2.0.0, otherwise the changes in dune files look good.

[Julow]

Nice. I agree this should be in the changelog.
Compatibility is not necessarily a concern as upgrading OCamlformat itself is involved and I don't expect users to upgrade it as soon as possible.

[emillon]

I agree with the changelog. We can wait a bit until the dune 2 issues are identified.

[XVilka]

There might be a problem with Dune >= 2.0 migration - some popular packages still depend on the jbuilder (jbuilder.transition) that is incompatible with the newer dune, so you wouldn't be able to install the ocamlformat in the opam switches with these packages installed:

• [new release] atdgen-codec-runtime, atd, atdgen-runtime, atds, atdj and atdgen (2.1.0) ocaml/opam-repository#15444
• Make a new release (due to jbuilder obsolescence) djs55/ocaml-sha#43
• probably some more, these I just met myself with opam list --installed --depends jbuilder.transition

P.S. You might want to rebase your PR.

[jberdine]

Since jbuilder and dune 2 can be co-installed, aren't those packages that depend on jbuilder.transition instead of jbuilder just broken?

[XVilka]

@jberdine I am not sure, opam doesn't allow me to upgrade those precisely because of that dependency on jbuilder:

Everything as up-to-date as possible (run with --verbose to show unavailable upgrades).

The following packages are not being upgraded because the new versions conflict with other installed packages:
  - dune.2.1.2
    ∗ jbuilder.transition is installed and requires dune < 2.0
  - dune-configurator.2.1.2

[emillon]

You can still fix these packages, or use an older version of ocamlformat.

The current situation with dependencies is not ideal: since at the moment you have to build ocamlformat in the same switch as your sources, it also induces a constraint on base and other ocamlformat dependencies. But that's not strictly required: a binary is just a binary, it does not depend on dune or base at runtime. It will be a nicer solution if we can fix that at the opam level.

[jberdine]

at the moment you have to build ocamlformat in the same switch as your sources

There must be some context I'm missing. I almost never build ocamlformat from the same switch as used for the code it formats.

[emillon]

I mean if you rely on opam to install ocamlformat as test-dep or something like that. I agree with you that it's best to do it in a separate switch (that's effectively what ocaml-ci is doing), but there's no way to tell opam to do that for now.

[emillon]

I just rebased this; not sure what's going on with the ocp-indent tests. (I tried to force >= 1.8.1 in case of a different version but that did not fix the issue)

[Julow]

There seems to be a problem with dune build @fmt. It seems that test/.ocamlformat_ignore wasn't useful and formatting of tests were disabled by something else. Could it be that test/passing/dune-project was overriding (using fmt) (by not specifying it) from ./dune-project ?

The reason test/.ocamlformat_ignore is not working is that it should be called test/.ocamlformat-ignore.

[emillon]

Formatting rules were not set up by default as the project was a 1.x. In a 2.x project it's necessary to disable them using (formatting disabled). I fixed this part.

[emillon]

and this is working. nice catch, thanks!

[gpetiot]

Looks good, thanks!

[Julow]

After that, I think we can merge !