dune subst issues with OCaml-CI

[mtelvers]

Expected Behavior

Up to Dune 3.16.1, dune subst (invoked by opam), in an directory containing just an .opam file completed without error. Since 3.17 an error is returned.

This issue relates to #11200, which was fixed by #11204, however, the two cases are different as #11200 covered completely empty directories by filtering them out, but this has not fixed OCaml-CI as OCaml-CI populates the directories with .opam files.

Actual Behavior

$ dune subst
File ".", line 1, characters 0-0:
Error: There is no dune-project file in the current directory, please add one
with a (name <name>) field in it.
Hint: 'dune subst' must be executed from the root of the project.

Reproduction

• PR with a reproducing test: dune subst test for directory containing just a .opam file #11291

3.16

$ mkdir dune-subst
$ cd dune-subst/
$ echo 'authors: [ "John Doe <[email protected]>" ]' > foo.opam
$ dune --version
3.16.0
$ dune subst
$ echo $?
0

3.17.1

$ mkdir dune-subst
$ cd dune-subst/
$ echo 'authors: [ "John Doe <[email protected]>" ]' > foo.opam
$ dune --version
3.17.1
$ dune subst
File ".", line 1, characters 0-0:
Error: There is no dune-project file in the current directory, please add one
with a (name <name>) field in it.
Hint: 'dune subst' must be executed from the root of the project.

Specifications

• Version of dune (output of dune --version): >= 3.17.0
• Version of ocaml (output of ocamlc --version): 4.14.2
• Operating system (distribution and version): Ubuntu 22.04.4