Fix ppx flags with (staged_pps ...) (#1218)

Signed-off-by: Jeremie Dimino <jeremie@dimino.org>

CHANGES.md

@@ -42,6 +42,8 @@ next
   wrapped modules but keep unwrapped modules with a deprecation message to
   preserve compatibility. (#1188, fix #985, @rgrinberg)
 
+- Fix the flags passed to the ppx rewriter when using `staged_pps` (#1218, @diml)
+
 1.1.1 (08/08/2018)
 ------------------
 

src/ordered_set_lang.ml

@@ -272,6 +272,13 @@ module Unexpanded = struct
 
   let standard = standard
 
+  let of_strings ~pos l =
+    { ast = Ast.Union (List.map l ~f:(fun x ->
+        Ast.Element (String_with_vars.virt_text pos x)))
+    ; loc = Some (Loc.of_pos pos)
+    ; context = Univ_map.empty
+    }
+
   let field ?(default=standard) ?check name =
     let dparse =
       match check with

src/ordered_set_lang.mli

@@ -80,6 +80,8 @@ module Unexpanded : sig
   include Dsexp.Sexpable with type t := t
   val standard : t
 
+  val of_strings : pos:string * int * int * int -> string list -> t
+
   val field
     :  ?default:t
     -> ?check:unit Dsexp.Of_sexp.t

src/preprocessing.ml

@@ -49,8 +49,10 @@ module Driver = struct
           (let%map loc = loc
            and flags = Ordered_set_lang.Unexpanded.field "flags"
            and as_ppx_flags =
-             Ordered_set_lang.Unexpanded.field "flags"
-               ~check:(Syntax.since syntax (1, 1))
+             Ordered_set_lang.Unexpanded.field "as_ppx_flags"
+               ~check:(Syntax.since syntax (1, 2))
+               ~default:(Ordered_set_lang.Unexpanded.of_strings ["--as-ppx"]
+                           ~pos:__POS__)
            and lint_flags = Ordered_set_lang.Unexpanded.field "lint_flags"
            and main = field "main" string
            and replaces =

test/blackbox-tests/test-cases/dune-ppx-driver-system/run.t

@@ -69,7 +69,7 @@ Test that going throught the -ppx option of the compiler works
   $ dune build test_ppx_staged.cma
       ocamldep .test_ppx_staged.objs/test_ppx_staged.ml.d
   tool name: ocamldep
-  args:--cookie library-name="test_ppx_staged"
+  args:--as-ppx --cookie library-name="test_ppx_staged"
         ocamlc .test_ppx_staged.objs/test_ppx_staged.{cmi,cmo,cmt}
   tool name: ocamlc
-  args:--cookie library-name="test_ppx_staged"
+  args:--as-ppx --cookie library-name="test_ppx_staged"