Package management should Ignore unused opam files when pinning

[giltho]

This is feedback on the dune package management preview.

I have a file a project that pins another project, but it fails to build with Error: unexpected version because of some empty but unused opam files in the project.

It works after just adding one line to the relevant opam files. See rems-project/cerberus#817

[rgrinberg]

Thanks. Dune can infer projects from one of two sources:

1. The project file
2. The .opam files

The project file doesn't define any packages so dune goes for 2. AFAIK, an opam file with the version incantation is invalid. So I don't think there's anything we can do here.

[rgrinberg]

Can you post your pins stanza? Maybe we can make the loading a little lazier.

[giltho]

I deleted that branch but I think it was simply

(pin
 (package
  (name cerberus-lib))
 (url
  "git+https://github.com/giltho/cerberus#6316f8f46dd8d6b207b8669c6ec082f78032e538"))

Yeah, I kind of understand that, ideally, all opam files should be correct. But empty opam files exist in many places because people don't generate them from dune-projects and dune refuses to build public modules without a corresponding opam file.

One or both of the following could be done:

• newer versions of dune could require the opam file to be valid (i.e. at least contain the version) in order to compile a public module, and if not issue at least a warning.
• If an opam file is detected to be empty, dune can just load use the default "empty" opam file that only contains 'opam-version: "2.0"'. It'd be a wrapper around the current function that loads the opam file, even if it's not pretty.

I do understand if option 2 is not desirable, and I can see that it doesn't appear, but on the issue now, but I clicked "Feature request" and not "Bug report" when I created this issue. I don't believe this is a bug, the current behaviour is acceptable, but it is worth flagging

[Leonidas-from-XIV]

AFAIK, an opam file with the version incantation is invalid.

Yes, that's true. The shortest valid OPAM file is

opam-version: "2.0"