refactor(pkg): move [partition_three] to [Stdune.List] (#11280)

Signed-off-by: Rudi Grinberg <[email protected]>

otherlibs/stdune/src/list.ml

@@ -262,3 +262,14 @@ let intersperse xs ~sep =
   in
   loop [] xs
 ;;
+
+let rec partition_three xs ~f =
+  match xs with
+  | [] -> [], [], []
+  | first :: rest ->
+    let xs, ys, zs = partition_three ~f rest in
+    (match f first with
+     | `Left x -> x :: xs, ys, zs
+     | `Middle y -> xs, y :: ys, zs
+     | `Right z -> xs, ys, z :: zs)
+;;

otherlibs/stdune/src/list.mli

@@ -18,6 +18,11 @@ val concat_map : 'a t -> f:('a -> 'b t) -> 'b t
 val partition_map : 'a t -> f:('a -> ('b, 'c) Either.t) -> 'b t * 'c t
 val rev_partition_map : 'a t -> f:('a -> ('b, 'c) Either.t) -> 'b t * 'c t
 
+val partition_three
+  :  'a t
+  -> f:('a -> [ `Left of 'x | `Middle of 'y | `Right of 'z ])
+  -> 'x list * 'y list * 'z list
+
 type ('a, 'b) skip_or_either =
   | Skip
   | Left of 'a

src/dune_pkg/opam_solver.ml

@@ -448,8 +448,8 @@ module Solver = struct
     let implementations = function
       | Virtual (_, impls) -> Fiber.return { impls }
       | Real role ->
-        let context = role.context in
         let+ impls =
+          let context = role.context in
           Context.candidates context role.name
           >>| List.filter_map ~f:(function
             | _, Error _rejection -> None
@@ -570,21 +570,10 @@ module Solver = struct
     | None -> Error req
   ;;
 
-  let rec partition_three f = function
-    | [] -> [], [], []
-    | first :: rest ->
-      let xs, ys, zs = partition_three f rest in
-      (match f first with
-       | `Left x -> x :: xs, ys, zs
-       | `Middle y -> xs, y :: ys, zs
-       | `Right z -> xs, ys, z :: zs)
-  ;;
-
   let pp_rolemap ~verbose reasons =
     let good, bad, unknown =
-      reasons
-      |> Solver.Output.RoleMap.bindings
-      |> partition_three (fun (role, component) ->
+      Solver.Output.RoleMap.bindings reasons
+      |> List.partition_three ~f:(fun (role, component) ->
         match Diagnostics.Component.selected_impl component with
         | Some impl when Diagnostics.Component.notes component = [] -> `Left impl
         | _ ->