Expose to/from_compiler in Astlib.Longident

CHANGES.md

@@ -7,6 +7,10 @@ unreleased
 
 ### Other Changes
 
+- Add `Longident.to/of_compiler` to astlib to simplify maintenance
+  of ppx-es that interacts with other parts of the compiler-libs such
+  as the type checker. (#603, @NathanReb)
+
 - Fix a bug where some infix operators such as `mod` would be printed as
   raw identifiers by our `Pprintast`. (#601, @NathanReb)
 

astlib/ast_504.ml

@@ -1,5 +1,5 @@
 module Longident = struct
-  type t (*IF_CURRENT = Ocaml_common.Longident.t *) =
+  type t = Longident_504.t =
     | Lident of string
     | Ldot of t Location.loc * string Location.loc
     | Lapply of t Location.loc * t Location.loc

astlib/longident.ml

@@ -29,3 +29,28 @@ let parse s =
       (* should not happen, but don't put assert false
                           so as not to crash the toplevel (see Genprintval) *)
   | Some v -> v
+
+let rec to_504_plus lid =
+  let loc = Location.none in
+  match lid with
+  | Lident s -> Longident_504.Lident s
+  | Ldot (lid, s) ->
+    Longident_504.Ldot ({txt = to_504_plus lid; loc}, { txt = s; loc})
+  | Lapply (lid, lid2) ->
+    Longident_504.Lapply
+      ({txt = to_504_plus lid; loc}, {txt= to_504_plus lid2; loc})
+
+let rec from_504_plus lid =
+  match lid with
+  | Longident_504.Lident s -> Lident s
+  | Longident_504.Ldot (lid, s) -> Ldot (from_504_plus lid.txt, s.txt)
+  | Longident_504.Lapply (lid, lid2) ->
+    Lapply (from_504_plus lid.txt, from_504_plus lid2.txt)
+
+let to_compiler lid =
+  (*IF_NOT_AT_LEAST 504 lid *)
+  (*IF_AT_LEAST 504 to_504_plus lid *)
+
+let from_compiler lid =
+  (*IF_NOT_AT_LEAST 504 lid *)
+  (*IF_AT_LEAST 504 from_504_plus lid *)

astlib/longident.mli

@@ -13,3 +13,7 @@ val flatten : t -> string list
 
 val parse : string -> t
 (** Parse a string into a long identifier built upon [Lident] and [Ldot]. *)
+
+val to_compiler : t -> Ocaml_common.Longident.t
+
+val from_compiler : Ocaml_common.Longident.t -> t

astlib/longident_504.ml

@@ -0,0 +1,5 @@
+type t =
+  (*IF_AT_LEAST 504 Ocaml_common.Longident.t = *)
+  | Lident of string
+  | Ldot of t Location.loc * string Location.loc
+  | Lapply of t Location.loc * t Location.loc

astlib/longident_504.mli

@@ -0,0 +1,5 @@
+type t =
+  (*IF_AT_LEAST 504 Ocaml_common.Longident.t = *)
+  | Lident of string
+  | Ldot of t Location.loc * string Location.loc
+  | Lapply of t Location.loc * t Location.loc