From a629a622b03dfa990505037b0ec6e7d67e5e9846 Mon Sep 17 00:00:00 2001
From: Pierrick Couderc <pierrick.couderc@nomadic-labs.com>
Date: Thu, 13 Nov 2025 11:32:58 +0100
Subject: [PATCH] Proto/Michelson: improve the trace for unpackable types

---
 .../lib_client/michelson_v1_error_reporter.ml         |  8 ++++++++
 src/proto_alpha/lib_protocol/script_ir_translator.ml  |  2 +-
 src/proto_alpha/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_alpha/lib_client/michelson_v1_error_reporter.ml b/src/proto_alpha/lib_client/michelson_v1_error_reporter.ml
index 366a0169c7d5..a6bce438a98c 100644
--- a/src/proto_alpha/lib_client/michelson_v1_error_reporter.ml
+++ b/src/proto_alpha/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_alpha/lib_protocol/script_ir_translator.ml b/src/proto_alpha/lib_protocol/script_ir_translator.ml
index 05e30ca6ee1a..ae5fe7aaa8aa 100644
--- a/src/proto_alpha/lib_protocol/script_ir_translator.ml
+++ b/src/proto_alpha/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_alpha/lib_protocol/script_tc_errors.ml b/src/proto_alpha/lib_protocol/script_tc_errors.ml
index d3e8855e3807..1b542fa1ba7a 100644
--- a/src/proto_alpha/lib_protocol/script_tc_errors.ml
+++ b/src/proto_alpha/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_alpha/lib_protocol/script_tc_errors_registration.ml b/src/proto_alpha/lib_protocol/script_tc_errors_registration.ml
index a24e2c6545bf..9870e53b79a1 100644
--- a/src/proto_alpha/lib_protocol/script_tc_errors_registration.ml
+++ b/src/proto_alpha/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
-- 
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