Add a reproduction case for issue #4429

[craigfe]

No description provided.

[ghost]

Thanks for the repro case. Could you use dune-build-info instead of the cache to reproduce this bug? @snowleopard is doing some restructuring of the code for the shared cache and the cache will stop calling git. So this repro case will soon stop working.

[snowleopard]

Thanks for the repro case. Could you use dune-build-info instead of the cache to reproduce this bug? @snowleopard is doing some restructuring of the code for the shared cache and the cache will stop calling git. So this repro case will soon stop working.

Thanks, indeed.

@craigfe After some upcoming changes, Dune cache will no longer require VCS information. The only reason it currently needs it is to support bulk download of build artifacts corresponding to a given commit but we found that in practice downloading artifacts for individual rules is simpler and fast enough.

[craigfe]

Thanks both. I've altered the reproduction to avoid Dune caching.

I wasn't able to get a reproduction w/ dune-build-info. Interestingly, the following works just fine:

  Initialized empty Git repository in $TESTCASE_ROOT/.git/
  $ echo "(executable (name main) (libraries dune-build-info))" > dune
  $ cat >main.ml <<EOF
  > ;; Printf.printf "internal version: %s\n"
  > ( match Build_info.V1.version () with
  > | None -> "None"
  > | Some v -> Build_info.V1.Version.to_string v )
  > EOF
  $ dune exec ./main.exe
  Info: Creating file dune-project with this contents:
  | (lang dune 2.8)
  internal version: None

(Probably just me missing something obvious.) I had a quick look through the internals, but couldn't work out why the emitted vcs-describe placeholder isn't translated into a failing Git command somewhere. Will take a deeper look at some point when I get the time; dune-build-info seems a more compelling reproduction than dune subst.

[ghost]

It's because we don't include the actual info when building executables in the _build directory. This is so that dune-build-info doesn't hurt incrementality, otherwise we'd end up rebuilding a bunch of stuff everytime we do a commit. There are two ways of getting the actual info:

• with dune install
• by adding (promote (until-clean)) to the executable stanza to make dune promote the exe

[craigfe]

Thanks for the explanation :-) Now using dune-build-info properly.

[ghost]

Looks good.