What compilation flags does Dune use by default?

Learning
1

Heya!

I’m trying to understand what compilation flags dune runs with by default. I know we can set up envs like this

(env
 (dev
  (flags (:standard -w +42)))
 (release
  (ocamlopt_flags (:standard -O3))))

and then run dune build --profile release for it to run optimized. I wonder though, if I just run dune build without adding any env or flags, does it do any optimization whatsover then?

2

A good way to figure this kind of things is the --verbose flag. When passed to dune, every command executed by dune will be printed on stdout.

3

When running dune build, Dune uses the default profile, which is dev by deafult (but can be changed using the (profile <name>) stanza in dune-workspace). The difference between dev and release is that 1) warnings are not hard errors in the release profile, and 2) dev disables inlining across modules by passing -opaque, which speeds up recompilation.

Those are the defaults. One can then add/change flags as you did above to customize each profile to your liking.

Cheers,
Nicolas

4

That makes sense, thank you so much for the clarification!