rfc(pkg): progress indicator for downloads

[Alizter]

Problem

When we do:

dune pkg lock

it typically take some time because we are fetching or cloning in the background.

Proposal

We could have a download indicator that looks like the following:

[0.1/5.2 MiB] <spinny thing> Downloading opam-repository https://opam.ocaml.org

This would give users a much better experience when waiting.

Implementation

We use opam libraries to fetch and clone repos. We could modify the calls to git by parsing from git fetch and git clone:

--progress
           Progress status is reported on the standard error stream by default when
           it is attached to a terminal, unless -q is specified. This flag forces
           progress status even if the standard error stream is not directed to a
           terminal.

When we have these we then parse and display a nice status.

Related PRs

• Progress indicators on jobs: #8601
• Download friendly byte units: #8618

[rgrinberg]

Looks like a good idea to me. I think this might need modifications to action execution in the engine that will allow progress reporting.

[emillon]

FYI, a couple years ago I had a look at the various HTTP clients and I don't think any had a progress callback. (though that's more of a concern for the opam libs)