add progress reporting capability to fetch

[ulugbekna]

Adds progress reporting capability (as arguments) to fetch through all fetch "levels":

Nss.Fetch.fetch_v1 <- Smart_git.fetch <- Sync.fetch <- Git_unix/Mem.fetch

[dinosaure]

Thanks!

[hannesm]

I'm curious why pass through such callbacks, where logs is already used, and there could be a log source (enable/disable via the Logs library) to modify the output of log messages?

[dinosaure]

I think this choice should be made by the end user - currently such outputs is printed by git and we should be able to do the same (and use something like Fmt.pr/Fmt.epr). Of course, in most of cases, the best is to report that with Logs.

[hannesm]

I don't quite understand. My question is: why should there be two ways to receive output of the git library -- one using Logs (for debug / warnings / errors) -- the other passing through stdout and stderr arguments. To me, such a API design is quite confusing.

[dinosaure]

I don't quite understand. My question is: why should there be two ways to receive output of the git library -- one using Logs (for debug / warnings / errors) -- the other passing through stdout and stderr arguments. To me, such a API design is quite confusing.

Ah I think, you refer to the old implementation of ocaml-git which shows (with logs) these outputs. With the new version, I used ignore so, these outputs are neither printed out into logs nor printed out with Fmt.pr/Fmt.epr. This PR wants to expose the ability to choose something like Logs or Fmt.pr/Fmt.epr (into a binary such as ogit-fetch).

Currently, the default is ignore but it was not properly exposed to the {Git_unix,Mem}.Sync module. This PR wants to fix that 👍.

[hannesm]

with this change, I get compilation errors in irmin-git (from @dinosaure's ocaml-git branch):

       Values do not match:
         val fetch :
           resolvers:'a ->
           'b -> 'c -> ?version:'d -> ?capabilities:'e -> 'f -> 'g
       is not included in
         val fetch :
           ?push_stdout:(string -> unit) ->
           ?push_stderr:(string -> unit) ->
           resolvers:Conduit.resolvers ->
           Smart_git.endpoint ->
           G.t ->
           ?version:[> `V1 ] ->
           ?capabilities:Smart.Capability.t list ->
           [ `All | `None | `Some of Git__.Reference.t list ] ->
           ((G.hash * (Git__.Reference.t * G.hash) list) option, error)
           result Lwt.t
       File "src/git/sync.mli", lines 27-36, characters 2-67:
         Expected declaration
       File "src/irmin-git/irmin_git.ml", line 1075, characters 6-11:
         Actual declaration