WIP: Lavyek backend

[balat]

This is a first attempt to write a Lavyek backend for Irmin. I did that as an experiment and also to learn the code. I managed to make it work in the toplevel with the following example:

#require "eio_main"
#require "digestif.c"
#require "irmin-watcher"
#require "irmin-lavyek"
#require "irmin.unix"

module Store = Irmin_lavyek.KV.Make (Irmin.Contents.String)
module Info = Irmin_unix.Info (Store.Info)

let value = "pouette"

let () =
  Eio_main.run @@ fun env ->
  Irmin_watcher.run @@ fun () ->
  let config = Irmin_lavyek.config ~fs:env#fs ~root:"/tmp/irminlavyek" in
  let repo = Store.Repo.v config in
  let main_branch = Store.main repo in
  Store.set_exn main_branch [ "a"; "b"; "c" ] value
    ~info:(Info.v ~author:"Example" "my first commit");
  let x = Store.get main_branch [ "a"; "b"; "c" ] in
  if value = x then print_endline "ok" else print_endline "ko"

Many functions are still not implemented (and some are probably missing in Lavyek).
Install:

opam pin add irmin-lavyek .

[clecat]

I did some changes to the branch:

• Added a proper configuration
• Added an mli file for irmin_lavyek
• Updated v function to allow fresh stores
• Corrected set function
• Added various logs
• Added remove implementation
• Removed locks, lavyek should support parrallel additions.

[clecat]

A new example would be:

#require "eio_main"
#require "digestif.c"
#require "irmin-watcher"
#require "irmin-lavyek"
#require "irmin.unix"

module Store = Irmin_lavyek.KV.Make (Irmin.Contents.String)
module Info = Irmin_unix.Info (Store.Info)

let value = "pouette"

let () =
  Eio_main.run @@ fun env ->
  Eio.Switch.run @@ fun sw ->
  Irmin_watcher.run @@ fun () ->
  let fs = env#fs in
  let path = Eio.Path.(fs / "/tmp/irmin-lavyek") in
  let config = Irmin_lavyek.config ~sw ~fs path in
  let repo = Store.Repo.v config in
  let main_branch = Store.main repo in
  Store.set_exn main_branch [ "a"; "b"; "c" ] value
    ~info:(Info.v ~author:"Example" "my first commit");
  let x = Store.get main_branch [ "a"; "b"; "c" ] in
  if value = x then print_endline "ok" else print_endline "ko";
  Store.Repo.close repo

[clecat]

Here are tasks that we might want to do (non-exhaustive):

• Allow iteration (need to change lavyek)
• Allow clear (need to change lavyek)
• Stats, for benchmarking purposes (need to change lavyek)
• Add tests, similarly to irmin-fs
• Allow list (need to change lavyek ? Or maybe mimic it by adding a second lavyek store which stores the "path hierarchy", unsure)

[clecat]

I added the irmin-test suite on the lavyek side, I'll put my changes when ready not on master but on a branch named irmin-lavyek, in order to keep the main branch clean until someone makes the changes in the optimal way (the key removal not being optimal).

[clecat]

When testing changes on lavyek, I met a big issue with irmin-lavyek:
Irmin creates 4 different lavyek stores, but if we do not separate them, they start corrupting each other.
The last commit uses the different Maker interfaces and adds a suffix to the root of the different stores.

[clecat]

I have rebased this PR over the eio branch now that the PR #2280 has been merged, however we will still have to make lavyek public to get the CI running.