We have been seeing a weird behavior of opam, both in CI and on dev machines, where a package that hasn't seen a change in months gets recompiled once in a while by opam. It is hard to investigate, we don't see much in opam logs, even when increasing the verbosity. And we can't systematically reproduce.

The message we get looks like this. Here it is on opam upgrade --fixup but I believe that it happens on basic opam upgrade too.

[06:14:31 #] opam upgrade --fixup
The following actions will be performed:
  ↻ recompile ocurl                           20231103+git
          [upstream or system changes]

The package definition is like this

opam-version: "2.0"
name: "ocurl"
maintainer: "ygrek@autistici.org"
homepage: "https://ygrek.org/p/ocurl"
license: "MIT"
authors: [ "Lars Nilsson" "ygrek" ]
dev-repo: "git+https://github.com/ygrek/ocurl.git"
bug-reports: "https://github.com/ygrek/ocurl/issues"
build: [
]
depends: [
  "curl" {= version}
]
synopsis: "Transitional dummy package: ocurl -> curl"
description: "Use `opam install curl`"

Our repository is a local repo (with the file:/// prefix).

It happens at least with opam 2.2.0~alpha3 and 2.1.2.

This is one of the reasons behind our request for #5776.