From 861bf10583db9ca455f0ed11d12eb4bc876ed42b Mon Sep 17 00:00:00 2001
From: Pierrick Couderc <pierrick.couderc@nomadic-labs.com>
Date: Thu, 13 Nov 2025 14:21:06 +0100
Subject: [PATCH 1/2] Proto/T: improve the trace for unpackable types

---
 .../lib_client/michelson_v1_error_reporter.ml         |  8 ++++++++
 .../lib_protocol/script_ir_translator.ml              |  2 +-
 .../lib_protocol/script_tc_errors.ml                  |  2 ++
 .../lib_protocol/script_tc_errors_registration.ml     | 11 +++++++++++
 4 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/src/proto_024_PsD5wVTJ/lib_client/michelson_v1_error_reporter.ml b/src/proto_024_PsD5wVTJ/lib_client/michelson_v1_error_reporter.ml
index 366a0169c7d5..a6bce438a98c 100644
--- a/src/proto_024_PsD5wVTJ/lib_client/michelson_v1_error_reporter.ml
+++ b/src/proto_024_PsD5wVTJ/lib_client/michelson_v1_error_reporter.ml
@@ -426,6 +426,14 @@ let report_errors ~details ~show_source
           loc ;
         if rest <> [] then Format.fprintf ppf "@," ;
         print_trace locations rest
+    | Environment.Ecoproto_error (Unpackable_type loc) :: rest ->
+        Format.fprintf
+          ppf
+          "%aValue has a type that cannot be packed"
+          print_loc
+          loc ;
+        if rest <> [] then Format.fprintf ppf "@," ;
+        print_trace locations rest
     | Environment.Ecoproto_error (Runtime_contract_error contract) :: rest ->
         Format.fprintf
           ppf
diff --git a/src/proto_024_PsD5wVTJ/lib_protocol/script_ir_translator.ml b/src/proto_024_PsD5wVTJ/lib_protocol/script_ir_translator.ml
index b91d2d871142..ac443596f3e9 100644
--- a/src/proto_024_PsD5wVTJ/lib_protocol/script_ir_translator.ml
+++ b/src/proto_024_PsD5wVTJ/lib_protocol/script_ir_translator.ml
@@ -1114,7 +1114,7 @@ let check_packable ~allow_contract loc root =
     | Chest_key_t -> return_unit
     | Chest_t -> return_unit
   in
-  check root
+  record_trace (Unpackable_type loc) (check root)
 
 type toplevel = {
   code_field : Script.node;
diff --git a/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors.ml b/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors.ml
index d3e8855e3807..1b542fa1ba7a 100644
--- a/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors.ml
+++ b/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors.ml
@@ -62,6 +62,8 @@ type error += Unexpected_operation of Script.location
 
 type error += Unexpected_contract of Script.location
 
+type error += Unpackable_type of Script.location
+
 type error += No_such_entrypoint of Entrypoint.t
 
 type error += Duplicate_entrypoint of Entrypoint.t
diff --git a/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors_registration.ml b/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors_registration.ml
index a24e2c6545bf..9870e53b79a1 100644
--- a/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors_registration.ml
+++ b/src/proto_024_PsD5wVTJ/lib_protocol/script_tc_errors_registration.ml
@@ -211,6 +211,17 @@ let () =
     (obj1 (req "loc" location_encoding))
     (function Unexpected_operation loc -> Some loc | _ -> None)
     (fun loc -> Unexpected_operation loc) ;
+  (* Unpackable type *)
+  register_error_kind
+    `Permanent
+    ~id:"michelson_v1.unpackable_type"
+    ~title:"Type cannot be packed (type error)"
+    ~description:
+      "When parsing script, a value was given to a primitive that expects a \
+       packable type."
+    (obj1 (req "loc" location_encoding))
+    (function Unpackable_type loc -> Some loc | _ -> None)
+    (fun loc -> Unpackable_type loc) ;
   (* No such entrypoint *)
   register_error_kind
     `Permanent
-- 
GitLab


From 88857ae6322c72110e5f9f137a0eb2264c4c3fe5 Mon Sep 17 00:00:00 2001
From: Pierrick Couderc <pierrick.couderc@nomadic-labs.com>
Date: Thu, 13 Nov 2025 14:30:00 +0100
Subject: [PATCH 2/2] Proto/T: Changelog: add an entry for new error messages
 for unpackable values

---
 docs/protocols/024_t024.rst | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/docs/protocols/024_t024.rst b/docs/protocols/024_t024.rst
index 813ce48fcdb7..7bec9fa44b99 100644
--- a/docs/protocols/024_t024.rst
+++ b/docs/protocols/024_t024.rst
@@ -46,6 +46,9 @@ Michelson
   the address has already been indexed through ``INDEX_ADDRESS``; it
   returns ``None`` otherwise. (MR :gl:`!18866`)
 
+- Improved error message when using non packable values with ``PACK``,
+  ``FAILWITH`` and ``EMIT``, and in parameters of partially applied
+  ``LAMBDA``. (MR :gl:`!19889`)
 
 Gas improvements
 ----------------
-- 
GitLab