Dune build-info : how to use?

Ecosystem
1

I am trying to display build info via using dune-build-info library. However, it always seems to be None. Looking at the documentation for Build_info.V1.Version.version, I can see it mentioned the following:

 (** The version at which the current executable was built. The version is
      [None] during development, it is only [Some _] once the executable is
      installed or promoted to the source tree. *)

What does promoted to the source tree mean?

I tried dune exec --profile release ./version.exe and also _build/default/version.exe. But both cases seem to give me None. The source is committed to a git repo. How does one get Some v?

B.

2

You need to install your program (dune install) or promote it by adding a (promote ..) field to your executable stanza, see Stanza Reference — Dune documentation.

Cheers,
Nicolas

1 Like
3

Thanks this finally did the trick.

$ cat dune
(executable
 (name version)
 (promote (until-clean))
 (libraries dune-build-info))

and calling dune promote and finally ./version.exe.

4

I am bit curious how this works? I manually copied the exe from _build and put it in the same dir. However, in that case I still get None. What does dune promote do? Does it do some processing to the .exe file?

5

When dune installs or promotes the executable, it physically overwrites some magic strings inside the executable with the version information. See the details at dune/src/dune_rules/artifact_substitution.ml at 5df2221179ff67e51ab93334ab2f8e42cdffb95b · ocaml/dune · GitHub

Cheers,
Nicolas

1 Like
6

Interesting, the documentation for promote doesn’t mention this and I can’t figure out from the source how a promote might be doing artifact substitution. Any pointers on where to look?

7

It is mentioned in the docs for the dune-build-info library Dune Libraries — Dune documentation.

Artifact substituion during promotion is done here: dune/src/dune_engine/target_promotion.ml at 7ce9e8eaf7b65645879c8974dc4f2c5e06876ffa · ocaml/dune · GitHub

Cheers,
Nicolas

1 Like