Check for errors when opening new ocaml files in Emacs

[Wilfred]

Otherwise, the user has to explicitly save the file before they can
see any merlin errors.

[trefis]

I don't think this has its place in merlin's default configuration:

• it's dubious that everyone would want this: it can slow down the opening of new files, it can be very noisy when you're opening a file in a project that isn't compiled yet, ...
• unless I'm mistaken, it's very easy to update your .emacs to have that behavior

Thank you for the suggestion though!

[rgrinberg]

I also agree that this seems like the wrong way to accomplish this. Is there a flycheck option to check a buffer after opening it? That would solve the problem in general.

[Wilfred]

Flycheck and flymake always check the buffer when you open the file, so that set my expectations. I also found it surprising that if I explicitly call M-x merlin-mode in a buffer, I don't see any merlin errors until I save.

It's possible to work around this in my own Emacs configuration, but my concern is that it's not discoverable. Have I missed something?

I'm less concerned about performance: I've tested this on an ocaml codebase with >100KLOC and >100 errors and it wasn't an issue. Flycheck is actually more aggressive than merlin: most checkers will update even if you don't save.

I suppose it's a question of whether you see merlin.el as primarily a code completion tool, or an error display package :)

[jberdine]

FWIW, maybe it's just me, but I not infrequently open files and explicitly do not want merlin to report errors, since the file has not been compiled, is at the other end of an only minimally-configured tramp connection, etc.

[rgrinberg]

Flycheck and flymake always check the buffer when you open the file, so that set my expectations. I also found it surprising that if I explicitly call M-x merlin-mode in a buffer, I don't see any merlin errors until I save.

So why doesn't it work in this case for you? Flycheck should drive this via https://github.com/flycheck/flycheck-ocaml. My main concern is such a setting shouldn't really be chosen at the mode level. It would be annoying to set this for ocaml, python, haskell, etc.

[Wilfred]

@jberdine FWIW I've been thinking of adding tramp support for Merlin, which would suit my workflow and maybe yours too?

@rgrinberg aha, I didn't realise that flycheck supported merlin! I see there's flycheck-ocaml which teaches flycheck how to use merlin. I only had flycheck itself.

[Wilfred]

I've added a note to the wiki page. Thanks for clarifying :)

[jberdine]

FWIW I've been thinking of adding tramp support for Merlin, which would suit my workflow and maybe yours too?

tramp support for merlin would be most excellent!

[Wilfred]

I did explore using flycheck with merlin, but it doesn't handle error ranges. It can't handle highlighting the part of the line that has the type error (see flycheck/flycheck-ocaml#12 and flycheck/flycheck#1400). At this point, I think merlin.el works better without flycheck.