Revert library redirect handling

Move library redirect creation back to [Gen_rules]. While this is less
elegant, the previous check in [Scope] was much more fragile. It relied
on a name collision to always be caused by a redirect, which is not
something that might be guaranteed in the future.

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

src/dune_rules/dune_file.ml

@@ -1918,25 +1918,31 @@ module Library_redirect = struct
   module Local = struct
     type nonrec t = (Loc.t * Lib_name.Local.t) t
 
+    let for_lib (lib : Library.t) ~new_public_name ~loc : t =
+      { loc; new_public_name; old_name = lib.name; project = lib.project }
+
+    let of_private_lib (lib : Library.t) : t option =
+      match lib.visibility with
+      | Public _
+      | Private None ->
+        None
+      | Private (Some package) ->
+        let loc, name = lib.name in
+        let new_public_name = (loc, Lib_name.mangled package.name name) in
+        Some (for_lib lib ~loc ~new_public_name)
+
     let of_lib (lib : Library.t) : t option =
       let open Option.O in
       let* public_name =
         match lib.visibility with
         | Public plib -> Some plib.name
-        | Private None -> None
-        | Private (Some package) ->
-          let loc, name = lib.name in
-          Some (loc, Lib_name.mangled package.name name)
+        | Private _ -> None
       in
       if Lib_name.equal (Lib_name.of_local lib.name) (snd public_name) then
         None
       else
-        Some
-          { loc = Loc.none
-          ; project = lib.project
-          ; old_name = lib.name
-          ; new_public_name = public_name
-          }
+        let loc = fst public_name in
+        Some (for_lib lib ~loc ~new_public_name:public_name)
   end
 end
 

src/dune_rules/dune_file.mli

@@ -365,6 +365,8 @@ module Library_redirect : sig
 
   module Local : sig
     type nonrec t = (Loc.t * Lib_name.Local.t) t
+
+    val of_private_lib : Library.t -> t option
   end
 end
 

src/dune_rules/gen_rules.ml

@@ -381,7 +381,15 @@ let filter_out_stanzas_from_hidden_packages ~visible_pkgs =
         | None -> true
         | Some package -> Package.Name.Map.mem visible_pkgs package.name
       in
-      Option.some_if include_stanza stanza)
+      if include_stanza then
+        Some stanza
+      else
+        match stanza with
+        | Library l ->
+          let open Option.O in
+          let+ redirect = Dune_file.Library_redirect.Local.of_private_lib l in
+          Dune_file.Library_redirect redirect
+        | _ -> None)
 
 let gen ~contexts ?only_packages conf =
   let open Fiber.O in

src/dune_rules/scope.ml

@@ -76,11 +76,9 @@ module DB = struct
                match (v1, v2) with
                | Found info1, Found info2 ->
                  Error (Lib_info.loc info1, Lib_info.loc info2)
-               | Found info, Redirect (loc, r)
-               | Redirect (loc, r), Found info -> (
-                 match Lib_name.analyze r with
-                 | Private _ -> Ok (Found_or_redirect.found info)
-                 | Public _ -> Error (loc, Lib_info.loc info) )
+               | Found info, Redirect (loc, _)
+               | Redirect (loc, _), Found info ->
+                 Error (loc, Lib_info.loc info)
                | Redirect (loc1, lib1), Redirect (loc2, lib2) ->
                  if Lib_name.equal lib1 lib2 then
                    Ok v1