Regression in #11028 when using `dune subst` on a project with an opam file

[btjorge]

I got notified of the closing of #10927, so I tried to test my opam file pin use-case, but the build failed with an error. Here's a reproduction test without opam :

Reproduction

$ mkdir test && cd test

$ cat > dune-project << EOF
(lang dune 3.17)
(name test)
(version 0.1)
(generate_opam_files)
(package (name test) (allow_empty))
EOF

$ dune build # generates the opam file

Previous Behavior

$ dune subst # does not fail

Actual Behavior

$ dune subst 
File "test.opam", line 1, characters 10-25:
1 | # This file is generated by dune, edit dune-project instead
              ^^^^^^^^^^^^^^^
Error: repository does not contain any version information

Note that the substitution works has expected

Specifications

• dune from main branch

[henrytill]

Did #11204 fix this?

There's a related issue (regression?) affecting users of opam-nix, where dune subst being run in a Nix build environment (where neither a git executable nor a .git directory are present) worked before without issue, but now, as of (lang dune 3.17), the subst step fails with the message reported above. Users can add (subst disabled) to their dune-project to work around this, but it's a regression from previous behavior where the default subst behavior was enabled outside of a Nix build environment, and fresh projects created with dune init proj worked with opam-nix out of the box.

Should I open a new issue for this?

[Blaisorblade]

Just got this issue with dune 3.17.2, git available and no Nix involved.

$ dune --version
3.17.2

My source folder contains both .git and an elpi-extra folder containing the .opam file — but I've opam-pinned the package, and that copies elpi-extra but of course not .git.

$ ls -d .git
.git
$ ls elpi-extra/
accumulate_bug  dune  dune-project  elpi-extra.opam  extra  grid.ml  LICENSE-BedRock  README.md  tests

[Richard-Degenne]

I am encountering the same problem: I have a dune project located in the subfolder of a Git repository, and that causes dune subst to fail. The easiest way to reproduce would be as follows.

mkdir dune-test && cd dune-test && \
git init && \
dune init proj subfolder && \
git add . && git commit --message "Initial commit" && \
cd subfolder && \
dune subst # /!\ Fails

---

Looking into the code, it seems to me that the problem resides in the way subst.ml resolves the current VCS: it lists the files in . and checks whether a .git entry exists (see Vcs.of_dir_contents. Because the .git folder of the repository lives in .., it fails to find it and incorrectly believes that the project lives outside of a VCS.

We can check that this is the case by turning our dune-test/subfolder into its own Git repository and trying dune subst again.

# In `dune-test/subfolder`
git init && git add . && git commit -m "Initial commit" && \
dune subst # No longer fails

Interestingly enough, @rgrinberg has already identified this since he left a comment:

  (* CR-someday rgrinberg: use [Source_tree.nearest_vcs] *)

So I guess the fix is pretty obvious? I'll try to submit a PR if I can, but I have never worked on Dune, so I need to see if this is in my wheelhouse. 😅

[Blaisorblade]

The "fixing" commit doesn't seem to fix the OP tho? It just fixes one part of the issue?

[btjorge]

The PR doesn't solve the issue but only a particular case. I don't have the permission to reopen it. Could you do it @rgrinberg ?

[maiste]

It seems some users are still affected. Reopening the issue but it requires some investigations.