refactor: move refmt/rescript_syntax hints to rules (#10795)

Signed-off-by: Rudi Grinberg <me@rgrinberg.com>

src/dune_engine/action.ml

@@ -70,19 +70,10 @@ module Prog = struct
 
     let create ?hint ~context ~program ~loc () = { hint; context; program; loc }
 
-    let user_message { context; program; hint; loc } =
-      let hint =
-        match program with
-        | "refmt" -> Some (Option.value ~default:"opam install reason" hint)
-        | "rescript_syntax" ->
-          Some (Option.value ~default:"opam install rescript-syntax" hint)
-        | _ -> hint
-      in
-      Utils.program_not_found_message ?hint ~loc ~context program
+    let raise { context; program; hint; loc } =
+      raise (User_error.E (Utils.program_not_found_message ?hint ~loc ~context program))
     ;;
 
-    let raise t = raise (User_error.E (user_message t))
-
     let to_dyn { context; program; hint; loc = _ } =
       let open Dyn in
       record

src/dune_rules/action_unexpanded.ml

@@ -405,7 +405,13 @@ end = struct
                  then Artifacts.Original_path
                  else Install_dir
                and* artifacts = Expander.artifacts env.expander in
-               Artifacts.binary ~loc:(Some loc) ~where artifacts s)
+               let hint =
+                 match s with
+                 | "refmt" -> Some "opam install reason"
+                 | "rescript_syntax" -> Some "opam install rescript-syntax"
+                 | _ -> None
+               in
+               Artifacts.binary ?hint ~loc:(Some loc) ~where artifacts s)
         in
         let prog = Result.map prog ~f:(Expander.map_exe env.expander) in
         let args = Value.L.to_strings ~dir args in