Allow ocaml.org to run while offline (#1366)

When offline, ocaml.org uses the current local state of opam-repository. This enables working on the codebase even when there is no Internet access.

src/ocamlorg_package/lib/opam_repository.ml

@@ -20,7 +20,9 @@ module Process = struct
 
   let exec cmd =
     let proc = Lwt_process.open_process_none cmd in
-    proc#status >|= check_status cmd
+    let open Lwt.Syntax in
+    let+ status = proc#status in
+    match status with Unix.WEXITED 0 -> Ok () | s -> Error (cmd, s)
 
   let pread cmd =
     let proc = Lwt_process.open_process_in cmd in
@@ -51,7 +53,7 @@ let last_commit () =
 
 let clone () =
   let open Lwt.Syntax in
-  let* () =
+  let* res =
     Process.exec
       ( "git",
         [|
@@ -61,13 +63,24 @@ let clone () =
           Fpath.to_string clone_path;
         |] )
   in
+  (match res with Ok () -> () | Error (c, s) -> Process.check_status c s);
   last_commit ()
 
 let pull () =
   let open Lwt.Syntax in
-  let* () =
+  let* pul =
     Process.exec (git_cmd [ "pull"; "-q"; "--ff-only"; "origin"; "master" ])
   in
+  (match pul with
+  | Ok () -> ()
+  | Error (_, Unix.WEXITED 1) ->
+      prerr_endline
+        "\n\
+         Pulling from opam repository was not possible. \n\
+         We will continue by building the package state\n\
+         using the existing local state of opam-repository.\n\
+         Some functionality might not work properly.\n"
+  | Error (c, s) -> Process.check_status c s);
   last_commit ()
 
 let fold_dir f acc directory =