commit fd604b269398aebdb0c5fa5511d9f3c38b6ecb45 (HEAD, origin/upgrade-ppxlib-0.18.0)
Author: Nathan Rebours <nathan.p.rebours@gmail.com>
Date:   Mon Oct 5 18:04:41 2020 +0200

    Make ppx_sexp_message compatible with ppxlib.0.18.0
    
    ppxlib.0.18.0 upgrades to the 4.11 AST which results in a change
    in string constants representation. This PR makes ppx_sexp_message
    compatible with the latest ppxlib.
    
    You might want for the actual release of ppxlib.0.18.0 before merging
    this!
    
    Signed-off-by: Nathan Rebours <nathan.p.rebours@gmail.com>

diff --git a/expander/ppx_sexp_message_expander.ml b/expander/ppx_sexp_message_expander.ml
index e0c2477..c801cd7 100644
--- a/expander/ppx_sexp_message_expander.ml
+++ b/expander/ppx_sexp_message_expander.ml
@@ -97,7 +97,7 @@ let sexp_of_expr ~omit_nil e =
   let e = rewrite_here e in
   let loc = { e.pexp_loc with loc_ghost = true } in
   match e.pexp_desc with
-  | Pexp_constant (Pconst_string ("", _)) -> Absent
+  | Pexp_constant (Pconst_string ("", _, _)) -> Absent
   | Pexp_constant const ->
     present_or_omit_nil ~loc ~omit_nil:false (sexp_of_constant ~loc const)
   | Pexp_constraint (expr, ctyp) -> sexp_of_constraint ~omit_nil ~loc expr ctyp
diff --git a/ppx_sexp_message.opam b/ppx_sexp_message.opam
index d8a6d95..3d6ef41 100644
--- a/ppx_sexp_message.opam
+++ b/ppx_sexp_message.opam
@@ -16,7 +16,7 @@ depends: [
   "ppx_here"      {>= "v0.14" & < "v0.15"}
   "ppx_sexp_conv" {>= "v0.14" & < "v0.15"}
   "dune"          {>= "2.0.0"}
-  "ppxlib"        {>= "0.11.0"}
+  "ppxlib"        {>= "0.18.0"}
 ]
 synopsis: "A ppx rewriter for easy construction of s-expressions"
 description: "