What compilation flags does Dune use by default?


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

  (flags (:standard -w +42)))
  (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?

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.

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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.


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