allow (wrapped (as name)) in library

This allows to specify the name of the top level module of a wrapped
library. Useful to be able to produce different libs with the same
module and then specify a dependency on either of these to choose the
implementation.

src/dune_lang/wrapped.ml

@@ -3,6 +3,7 @@ open Dune_sexp.Decoder
 
 type t =
   | Simple of bool
+  | Yes_as of string
   | Yes_with_transition of string
 
 let equal = Poly.equal
@@ -15,24 +16,31 @@ let decode =
       , Dune_sexp.Syntax.since Stanza.syntax (1, 2)
         >>> let+ x = string in
             Yes_with_transition x )
+    ; ( "as"
+      , Dune_sexp.Syntax.since Stanza.syntax (3, 9)
+        >>> let+ x = string in
+            Yes_as x )
     ]
 ;;
 
 let encode =
   let open Dune_sexp.Encoder in
   function
   | Simple b -> bool b
+  | Yes_as name -> pair string string ("as", name)
   | Yes_with_transition m -> pair string string ("transition", m)
 ;;
 
 let to_bool = function
   | Simple b -> b
+  | Yes_as _ -> true
   | Yes_with_transition _ -> true
 ;;
 
 let to_dyn =
   let open Dyn in
   function
   | Simple s -> variant "Simple" [ bool s ]
+  | Yes_as name -> variant "Yes_as" [ string name ]
   | Yes_with_transition s -> variant "Yes_with_transition" [ string s ]
 ;;

src/dune_lang/wrapped.mli

@@ -1,5 +1,6 @@
 type t =
   | Simple of bool
+  | Yes_as of string
   | Yes_with_transition of string
 
 val equal : t -> t -> bool

src/dune_rules/dune_file.ml

@@ -922,6 +922,8 @@ module Library = struct
        | Some _ -> This (Some (Module_name.of_local_lib_name t.name)))
     | None, This (Simple true | Yes_with_transition _) ->
       This (Some (Module_name.of_local_lib_name t.name))
+    | None, This (Yes_as name) ->
+      This (Some (Module_name.of_string name))
   ;;
 
   let to_lib_info

src/dune_rules/lib_rules.ml

@@ -126,7 +126,7 @@ let gen_wrapped_compat_modules (lib : Library.t) cctx =
   let transition_message =
     lazy
       (match Modules.wrapped modules with
-       | Simple _ -> assert false
+       | Simple _ | Yes_as _ -> assert false
        | Yes_with_transition r -> r)
   in
   Module_name.Map_traversals.parallel_iter wrapped_compat ~f:(fun name m ->

src/dune_rules/modules.ml

@@ -99,16 +99,16 @@ module Stdlib = struct
 
   let make ~(stdlib : Ocaml_stdlib.t) ~modules ~wrapped ~main_module_name =
     let modules =
-      match wrapped with
-      | Wrapped.Simple true | Yes_with_transition _ ->
+      match Wrapped.to_bool wrapped with
+      | true ->
         Module_name.Map.map modules ~f:(fun m ->
           if Module.name m = main_module_name || special_compiler_module stdlib m
           then m
           else (
             let path = [ main_module_name; Module.name m ] in
             let m = Module.set_path m path in
             Module.set_obj_name m (Module_name.Path.wrap path)))
-      | Simple false -> modules
+      | false -> modules
     in
     let unwrapped = stdlib.modules_before_stdlib in
     let exit_module = stdlib.exit_module in
@@ -713,7 +713,7 @@ module Wrapped = struct
     let wrapped_compat =
       match (wrapped : Dune_lang.Wrapped.t) with
       | Simple false -> assert false
-      | Simple true -> Module_name.Map.empty
+      | Simple true | Yes_as _ -> Module_name.Map.empty
       | Yes_with_transition _ ->
         let toplevel = Module_trie.toplevel_only modules in
         Module_name.Map.remove toplevel main_module_name
@@ -893,18 +893,18 @@ let lib ~obj_dir ~main_module_name ~wrapped ~stdlib ~lib_name ~implements ~modul
       let modules = Module_trie.to_map modules in
       Stdlib (Stdlib.make ~stdlib ~modules ~wrapped ~main_module_name)
     | None ->
-      (match wrapped, main_module_name, Module_trie.as_singleton modules with
-       | Simple false, _, Some m -> Singleton m
-       | Simple false, _, None ->
+      (match Dune_lang.Wrapped.to_bool wrapped, main_module_name, Module_trie.as_singleton modules with
+       | false, _, Some m -> Singleton m
+       | false, _, None ->
          let mangle = Mangle.Unwrapped in
          Unwrapped (Unwrapped.of_trie modules ~mangle ~obj_dir)
-       | (Yes_with_transition _ | Simple true), Some main_module_name, Some m ->
+       | true, Some main_module_name, Some m ->
          if Module.name m = main_module_name && not implements
          then Singleton m
          else make_wrapped main_module_name
-       | (Yes_with_transition _ | Simple true), Some main_module_name, None ->
+       | true, Some main_module_name, None ->
          make_wrapped main_module_name
-       | (Simple true | Yes_with_transition _), None, _ ->
+       | true, None, _ ->
          Code_error.raise "Modules.lib: cannot wrap without main module name" [])
   in
   with_obj_map modules