Improve: disable ocamlformat if no dot ocamlformat in the project

[hhugo]

The PR adds a way to not reformat files that live in a "project" that doesn't contain a .ocamlformat file.

[hhugo]

@samoht, @gpetiot, @jberdine, alternative suggestion welcome.

[jberdine]

IIUC, there is a similar situation with dune, which has resulted in a way of specifying subdirs to ignore. This would result in putting a config file in the dir containing the project root dir to be ignored, and adding that dir's name into the config. I'm not sure if that is better, but think that the space was explored at some length for dune.

[hhugo]

Just to be clear, the issue that this PR is trying to solve is about not formatting files that are not meant to be formatted. In particular, I don't want files from the ocaml compiler to be formatted when I edit them in emacs.

[jberdine]

I see. I guess perhaps I should enable format-on-save myself since it seems most people use it that way.

For that particular use case, you prefer to call ocamlformat and have it detect that it's disabled, rather than e.g. configuring emacs to not call ocamlformat in the first place? I'm thinking of for instance enabling format-on-save in tuareg-mode-hook only if the file name matches some user-specific whitelist.

This PR basically says to look for an .ocamlformat file in the ancestor directories of the input file, but stop looking when reaching a "project root" dir, right? I'm not sure the implementation is the simplest, but the basic approach seems good to me. We should document it in the man page where it discusses where .ocamlformat files are searched for.

Perhaps this stop at project root mode should be the default?

[hhugo]

I'm now curious about how you use ocamlformat if not with format-on-save. Some logic could be implemented in the emacs mode, but similar logic would then need to be implemented in other editor mode a well

[jberdine]

I'm low tech:

(add-hook
  'tuareg-mode-hook
  (lambda ()
    (define-key merlin-mode-map (kbd "M-q") 'ocamlformat)))

[samoht]

M-q only formats the current top-level expression, right? How do you do this without --lines? But maybe the expression is computed by tuareg mode already.

[jberdine]

My binding in merlin-mode-map shadows tuareg's, so it formats the whole buffer.

[hhugo]

I've reworked the PR.
The behaviour is now triggered by --inside-project-only (better name welcome).
This flags is now passed to ocamlformat in the emacs mode.
I've also added a --print-config flag that will print config updates together with their origin (see new tests)

[hhugo]

This PR should naturally support the addition of a --root option

[hhugo]

I've reverted the change to the emacs mode for now so that the behaviour is preserved (to be discussed in another PR)

[jberdine]

@hhugo I think it's ok to also push update out of the handler

[hhugo]

I've implemented your suggestion regarding parse, it now returns a result.

[jberdine]

Nice, thanks!

[jberdine]

nit: . at end.