On version pinning don't read archive opam file

[rjbou]

fix #4608

[kit-ty-kate]

Does this also return true when doing opam pin add pkg.version <repo>? In that case, there is no need to look into the archive/repo either

[kit-ty-kate]

I’m not sure what the entire if statement is trying to do in the first place.

"do not do anything (equivalent to --no-action) if e.g. doing something like opam pin add pkg.version <archive/repo> and the version number is the same as the one in the archive/repo" ? That seems a bit suspicious to me

[kit-ty-kate]

I had a go at trying to debug this suspicious if and i have a repro case:

$ cat test/dune.opam
opam-version: "2.0"
version: "2.0.1"
build: ["sh" "-c" "ls && false"]
url {
  src: "https://github.com/ocaml/dune/archive/main.tar.gz"
}
$ opam pin add dune.2.0.1 test/
[...]

#=== ERROR while compiling dune.2.0.1 =========================================#
# context     2.1.0 | linux/x86_64 | ocaml-variants.4.13.0+trunk | pinned(file:///home/opam/test)
# path        ~/.opam/4.13/.opam-switch/build/dune.2.0.1
# command     /bin/sh -c ls && false
# exit-code   1
# env-file    ~/.opam/log/dune-236-a0af0d.env
# output-file ~/.opam/log/dune-236-a0af0d.out
### output ###
# dune.opam

So I really think this whole if statement should be removed as a whole.

[rjbou]

It is not suspicious, that if statement is present for a reason: optimisation. If the package is version pinned, there is no need to retrieve it again / synchronise it. Maybe we can say/decide that this optimisation is not efficient, but that's another question.
opam pin add pkg.version <non-archive-url> is different than a version pin. In the first case, it is a path/git/etc pin with given version, while a version pin is "pin pkg with repo opam file at that version", so sources are taken from url archive (or repo, on official opam repository we take only archives url but they can be vcs ones), and is not prone to change/update unless the opam repository changes.
So if you opam pin add pkg.version url, it pins to path/vcs url, it takes the opam file from the url, and it needs to synchronise from it each time. The dune.2.0.1 pinning/install behavior is the wanted one.

We need to check opam pin pkg.version archive-url behavior, and see what we want for that.

We also need to add some pinning and downloading/syncing tests, to check and be sure that we don't sync more that we need.

"do not do anything (equivalent to --no-action) if e.g. doing something like opam pin add pkg.version <archive/repo> and the version number is the same as the one in the archive/repo"

From where is this citation? Maybe we need to clarify that doc.