R. Boujbel

It is the expected behavior as it is an parsing error and the field is not mandatory, so a _wrong_ checksum (because of an parse error) results on a missing...

In fact, we can simply retrieve the default page and drop the result.

> can the fallback be switched off, and/or does this affect purely offline use of opam with local files? The fallback is enabled by default, it can be disabled by...

~TODO: add non initialised information to have a more specific error message~

`opam lock` is [meant](https://github.com/ocaml/opam/wiki/Spec-for-opam-lock-integration) / [was designed](https://github.com/AltGr/opam-lock#opam-lock-restrict-opam-file-to-describe-a-precise-build-environment) to share a development setup: *I know that with these libraries versions my program/package compiles, I want to snapshot them* to share them...

Lock file does not keep local pinned dependencies (cf. #4897), it should work with external one.

For opam lock, there is no difference between local pin or pin-depends. It looks for installed dependencies, if it is pinned, adds it in the lock file (only if not...

External dependencies are always checked: at (almost) each run, opam capture their state, and warn if currently conf installed packages have no more their corresponding external dependency installed. The opam...

from dev meeting: We need to check synopsis & description usage. synopsis must not be empty, and description is optional. it's descr that is optional -> add a deprectaed message...

proposal: in this PR, we remove the descr reference, and in another, we deprecate and clean-up `OpamFile.Descr` usage