gnu: Add ocaml-ppx-sexp-message.

* gnu/packages/ocaml.scm (ocaml-ppx-sexp-message): New variable.

gnu/packages/ocaml.scm

@@ -5562,3 +5562,31 @@ many values).")
     (description "A ppx rewriter that simplifies building s-expressions from
 ocaml values.")
     (license license:asl2.0)))
+
+(define-public ocaml-ppx-sexp-message
+  (package
+    (name "ocaml-ppx-sexp-message")
+    (version "0.11.0")
+    (source (origin
+              (method url-fetch)
+              (uri (string-append "https://ocaml.janestreet.com/ocaml-core/v"
+                                  (version-major+minor version)
+                                  "/files/ppx_sexp_message-v" version ".tar.gz"))
+              (sha256
+               (base32
+                "1yh440za0w9cvrbxbmqacir8715kdaw6sw24ys9xj80av9nqpiw7"))))
+    (build-system dune-build-system)
+    (propagated-inputs
+      `(("ocaml-base" ,ocaml-base)
+        ("ocaml-ppx-here" ,ocaml-ppx-here)
+        ("ocaml-ppx-sexp-conv" ,ocaml-ppx-sexp-conv)
+        ("ocaml-migrate-parsetree" ,ocaml-migrate-parsetree)
+        ("ocaml-ppxlib" ,ocaml-ppxlib)))
+    (properties `((upstream-name . "ppx_sexp_message")))
+    (home-page "https://github.com/janestreet/ppx_sexp_message")
+    (synopsis "A ppx rewriter for easy construction of s-expressions")
+    (description "Ppx_sexp_message aims to ease the creation of s-expressions
+in OCaml.  This is mainly motivated by writing error and debugging messages,
+where one needs to construct a s-expression based on various element of the
+context such as function arguments.")
+    (license license:asl2.0)))