Error: Invalid dune file on Unicode in dune file

Expected Behavior

The path is treated like any other path.

Actual Behavior

File "dune", line 1, characters 16-16:
1 | (data_only_dirs что)

Error: Invalid dune file

Reproduction

Create a directory containing only a dune file with

(data_only_dirs что)

Run dune build.

It doesn't matter whether the directory что exists or not.

Specifications

• Version of dune (output of dune --version): 2.8.5
• Version of ocaml (output of ocamlc --version): 4.12.0
• Operating system (distribution and version): Ubuntu 20.04 on WSL1

Additional information

I encountered this while trying to build a project with Melange, which appears to have a bsb that is a wrapper for Dune. The wrapper emits an absolute path into a generated dune.bsb file, which in my case sometimes contains non-Latin characters. I don't actually have Cyrillics in my project proper.

Reproduce the issue with a dune file containing (data_only_dirs что) and run dune build. Start by tracing how the dune file parses the Unicode path; done means the path is accepted like any other path, whether or not the directory exists.