Add Process.run is_success

lib_eio/process.ml

@@ -84,12 +84,13 @@ let spawn ~sw (t:#mgr) ?cwd ?stdin ?stdout ?stderr ?env ?executable args =
     ?stdout:(stdout :> Flow.sink option)
     ?stderr:(stderr :> Flow.sink option)
 
-let run (t:#mgr) ?cwd ?stdin ?stdout ?stderr ?env ?executable args =
+let run (t:#mgr) ?cwd ?stdin ?stdout ?stderr ?is_success ?env ?executable args =
   Switch.run @@ fun sw ->
   let child = spawn ~sw t ?cwd ?stdin ?stdout ?stderr ?env ?executable args in
-  match await child with
-  | `Exited 0 -> ()
-  | status ->
+  match await child, is_success with
+  | `Exited 0, None -> ()
+  | `Exited code, Some f when f code -> ()
+  | status, _ ->
     let ex = err (Child_error status) in
     raise (Exn.add_context ex "running command: %a" pp_args args)
 

lib_eio/process.mli

@@ -113,11 +113,14 @@ val run :
   ?stdin:#Flow.source ->
   ?stdout:#Flow.sink ->
   ?stderr:#Flow.sink ->
+  ?is_success:(int -> bool) ->
   ?env:string array ->
   ?executable:string ->
   string list -> unit
 (** [run] does {!spawn} followed by {!await_exn}, with the advantage that if the process fails then
     the error message includes the command that failed.
+    When [is_success] is present, it is called with the exit code to determine whether it indicates success or failure.
+    Without [is_success], success requires the process to return an exit code of 0.
 
     Note: If [spawn] needed to create extra fibers to copy [stdin], etc, then it also waits for those to finish. *)
 

tests/process.md

@@ -148,6 +148,14 @@ Eio.Io Process Child_error Exited (code 3),
   running command: bash -c "exit 3" "" foo
 ```
 
+Exit code success can be determined by is_success:
+
+```ocaml
+# run @@ fun mgr env ->
+  Process.run ~is_success:(fun code -> Int.(code = 3)) mgr ["bash"; "-c"; "exit 3"; ""; "foo"];;
+- : unit = ()
+```
+
 The default environment:
 
 ```ocaml