Switch to ocaml-migrate-parsetree.driver-main

src/gen_rules.ml

@@ -168,6 +168,8 @@ module Gen(P : Params) = struct
       create findlib P.internal_libraries
         ~dirs_with_dot_opam_files:P.dirs_with_dot_opam_files
 
+    let find ~from name = find t ~from name
+
     module Libs_vfile =
       Vfile_kind.Make_full
         (struct type t = Lib.t list end)
@@ -178,7 +180,7 @@ module Gen(P : Params) = struct
         (struct
           open Sexp.Of_sexp
           let t dir sexp =
-            List.map (list string sexp) ~f:(Lib_db.find t ~from:dir)
+            List.map (list string sexp) ~f:(Lib_db.find_exn t ~from:dir)
         end)
 
     let vrequires ~dir ~item =
@@ -567,43 +569,55 @@ module Gen(P : Params) = struct
 
   let ppx_drivers = Hashtbl.create 32
 
-  let build_ppx_driver ~dir ~dep_kind ~target ~main pp_names ~driver =
+  let migrate_driver_main = "ocaml-migrate-parsetree.driver-main"
+
+  let build_ppx_driver ~dir ~dep_kind ~target pp_names ~driver =
     let mode = Mode.best in
     let compiler = Option.value_exn (Mode.compiler mode) in
+    let pp_names = pp_names @ [migrate_driver_main] in
     let libs =
       Lib_db.closure ~dir ~dep_kind (List.map pp_names ~f:Lib_dep.direct)
     in
     let libs =
-      (* Put the driver back at the end *)
+      (* Put the driver back at the end, just before migrate_driver_main *)
       match driver with
       | None -> libs
       | Some driver ->
         libs >>^ fun libs ->
-        let libs, driver =
+        let is_driver name = name = driver || name = migrate_driver_main in
+        let libs, drivers =
           List.partition_map libs ~f:(fun lib ->
             if (match lib with
-              | External pkg -> pkg.name = driver
+              | External pkg -> is_driver pkg.name
               | Internal (_, lib) ->
-                lib.name = driver ||
+                is_driver lib.name ||
                 match lib.public with
                 | None -> false
-                | Some { name; _ } -> name = driver)
+                | Some { name; _ } -> is_driver name)
             then
               Inr lib
             else
               Inl lib)
         in
-        libs @ driver
+        libs @ drivers
+    in
+    (* Provide a better error for migrate_driver_main given that this is an implicit
+       dependency *)
+    let libs =
+      match Lib_db.find ~from:dir migrate_driver_main with
+      | None ->
+        Build.fail { fail = fun () ->
+          die "@{<error>Error@}: I couldn't find '%s'.\n\
+               I need this library in order to use ppx rewriters.\n\
+               See the manual for details.\n\
+               Hint: opam install ocaml-migrate-parsetree"
+            migrate_driver_main
+        }
+        >>>
+        libs
+      | Some _ ->
+        libs
     in
-    add_rule
-      (Build.action ~targets:[main] (Write_file (main, {|(* File generated by jbuilder *)
-let () =
-  Printf.eprintf "%s: driver missing!
-If you see this message, it means that you are missing a ppx driver at the
-end of your list of preprocessors. Consult the manual for more details."
-    Sys.argv.(0);
-  exit 1
-|})));
     add_rule
       (libs
        >>>
@@ -612,7 +626,7 @@ end of your list of preprocessors. Consult the manual for more details."
        Build.run (Dep compiler)
          [ A "-o" ; Target target
          ; Dyn (Lib.link_flags ~mode)
-         ; Dep main ]);
+         ]);
     libs
 
   let ppx_dir = Path.of_string (sprintf "_build/.ppx/%s" ctx.name)
@@ -634,9 +648,8 @@ end of your list of preprocessors. Consult the manual for more details."
     | None ->
       let ppx_dir = Path.relative ppx_dir key in
       let exe = Path.relative ppx_dir "ppx.exe" in
-      let main = Path.relative ppx_dir "jbuilder_ppx_main.ml" in
       let libs =
-        build_ppx_driver names ~dir ~dep_kind ~target:exe ~main ~driver
+        build_ppx_driver names ~dir ~dep_kind ~target:exe ~driver
       in
       Hashtbl.add ppx_drivers ~key ~data:(exe, libs);
       (exe, libs)

src/lib_db.ml

@@ -24,7 +24,7 @@ let find_by_internal_name t ~from name =
   let scope = internal_name_scope t ~dir:from in
   String_map.find name !scope
 
-let find t ~from name =
+let find_exn t ~from name =
   match find_by_internal_name t ~from name with
   | Some x -> Lib.Internal x
   | None ->
@@ -32,6 +32,11 @@ let find t ~from name =
       ~f:(fun name ->
         External (Findlib.find_exn t.findlib name))
 
+let find t ~from name =
+  match find_exn t ~from name with
+  | exception _ -> None
+  | x -> Some x
+
 let find_internal t ~from name =
   match find_by_internal_name t ~from name with
   | Some _ as some -> some
@@ -111,18 +116,18 @@ let interpret_lib_deps t ~dir lib_deps =
   let libs, failures =
     List.partition_map lib_deps ~f:(function
       | Lib_dep.Direct name -> begin
-          match find t ~from:dir name with
+          match find_exn t ~from:dir name with
           | x -> Inl [x]
           | exception e ->
             (* Call [find] again to get a proper backtrace *)
-            Inr { fail = fun () -> ignore (find t ~from:dir name : Lib.t); raise e }
+            Inr { fail = fun () -> ignore (find_exn t ~from:dir name : Lib.t); raise e }
         end
       | Select { result_fn; choices } ->
         match
           List.find_map choices ~f:(fun { lits; _ } ->
             match
               List.filter_map lits ~f:(function
-                | Pos s -> Some (find t ~from:dir s)
+                | Pos s -> Some (find_exn t ~from:dir s)
                 | Neg s ->
                   if lib_is_installable t ~from:dir s then
                     raise Exit

src/lib_db.mli

@@ -10,7 +10,8 @@ val create
   -> (Path.t * Jbuild_types.Library.t) list
   -> t
 
-val find : t -> from:Path.t -> string -> Lib.t
+val find     : t -> from:Path.t -> string -> Lib.t option
+val find_exn : t -> from:Path.t -> string -> Lib.t
 
 val internal_libs_without_non_installable_optional_ones : t -> Lib.Internal.t list