Unable to pin or lock opam file with {= version}

[bikallem]

Hi,
Consider the following as part of an opam file (https://github.com/lemaetech/wtr/blob/main/wtr-ppx.opam):

depends: [
  "dune" {>= "2.8"}
  "ocaml" {>= "4.12.0"}
  "uri" {>= "4.2.0"}
  "wtr" {= "version"}
  "ppxlib" {>= "0.22.0"}
  "odoc" {with-doc}
]

When I issue the command opam pin . , I get the following error,

[ERROR] Package conflict!
  * Missing dependency:
    - wtr >= version
    no matching version

Due to this opam lock ./wtr-ppx.opam also fails with the following error:

[ERROR] Package conflict!
  * Missing dependency:
    - wtr >= version
    no matching version

It seems we can't pin or lock packages where the dependency constraint contains {= version}. I am using opam 2.1

[kit-ty-kate]

{= "version"} and {= version} are different things.

The first one says the version number is version (as in wtr-ppx.version).
The second one says the version number is [replace this by the version number of the current package] (in this case wtr-ppx.3.0.0)

To fix this you need to change your dune-project file in this way: lemaetech/wtr#12
This should regenerate the opam file correctly.

[kit-ty-kate]

That said this a common mistake and we could have a warning to help users figure this out

[AltGr]

Indeed; maybe the warning should probably be in dune though ? in this case the mistake in opam syntax is much more obvious

[kit-ty-kate]

A dedicated lint warning is probably the way to show this