From 0c03e7bc005051f8d1310f8b8f0ea43cd211d7f3 Mon Sep 17 00:00:00 2001
From: Christoph Knittel <ck@cca.io>
Date: Thu, 8 Oct 2026 17:50:55 +0000
Subject: [PATCH 1/2] Represent variant spread patterns with a
 Ppat_variant_spread node

A variant spread pattern ...t was Ppat_type, the node of the polymorphic
variant pattern #...t, with a res.patVariantSpread attribute telling the
two apart. It now has its own node; the v0 bridge keeps the old encoding
for PPXs. The type checker expands it as before, and it no longer counts as
a polymorphic variant pattern. The printer no longer needs to filter the
attribute.

Signed-off-by: Christoph Knittel <christoph@knittel.cc>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 CHANGELOG.md                                  |  1 +
 analysis/src/completion_front_end.ml          |  2 +-
 analysis/src/semantic_tokens.ml               |  2 +-
 analysis/src/utils.ml                         |  1 +
 compiler/ext/config.ml                        |  4 +--
 compiler/ml/ast_helper.ml                     |  1 +
 compiler/ml/ast_helper.mli                    |  1 +
 compiler/ml/ast_iterator.ml                   |  2 +-
 compiler/ml/ast_mapper.ml                     |  1 +
 compiler/ml/ast_mapper_from0.ml               | 16 ++++++++-
 compiler/ml/ast_mapper_to0.ml                 |  5 +++
 compiler/ml/depend.ml                         |  2 +-
 compiler/ml/parsetree.ml                      |  3 +-
 compiler/ml/pprintast.ml                      |  1 +
 compiler/ml/printast.ml                       |  3 ++
 compiler/ml/typecore.ml                       | 18 ++++------
 compiler/ml/variant_coercion.ml               |  6 ----
 compiler/syntax/src/res_ast_debugger.ml       |  5 +++
 compiler/syntax/src/res_comments_table.ml     |  2 +-
 compiler/syntax/src/res_core.ml               |  6 +---
 compiler/syntax/src/res_parsetree_viewer.ml   | 14 +-------
 compiler/syntax/src/res_parsetree_viewer.mli  |  1 -
 compiler/syntax/src/res_printer.ml            |  4 +--
 tests/ounit_tests/ounit_ast_mapper0_tests.ml  | 36 +++++++++++++++++++
 .../ast-mapping/VariantSpreadPatterns.res     | 10 ++++++
 .../expected/VariantSpreadPatterns.res.txt    | 10 ++++++
 .../pattern/expected/variantSpreads.res.txt   | 10 +++---
 27 files changed, 114 insertions(+), 53 deletions(-)
 create mode 100644 tests/syntax_tests/data/ast-mapping/VariantSpreadPatterns.res
 create mode 100644 tests/syntax_tests/data/ast-mapping/expected/VariantSpreadPatterns.res.txt

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 7991c353904..0e66a867b54 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -48,6 +48,7 @@
 #### :house: Internal
 
 - Remove the unused `res.iflet` encoding of `if let`, which the parser always rejects with a syntax error suggesting a `switch`. The error is unchanged. https://github.com/rescript-lang/rescript/pull/8741
+- Represent variant spread patterns (`...t`) with a dedicated `Ppat_variant_spread` parsetree node instead of `Ppat_type` with a `res.patVariantSpread` attribute, which remains only in the PPX wire representation. PR_LINK
 - Remove the obsolete `res.ternary` and `JSX` attributes from the formatter's internal attribute filters and merge the filters into one. https://github.com/rescript-lang/rescript/pull/8740
 - Represent `await` on module expressions with a dedicated `Pmod_await` parsetree node instead of a `res.await` attribute, which remains only in the PPX wire representation. https://github.com/rescript-lang/rescript/pull/8738
 - Remove dead compiler code: warning 24, the `J.String_index` JS IR node, the `Pisint` and `Parraysets` Lambda primitives with their unused `%` primitive names (`%obj_is_int`, `%obj_dup`, `%obj_field`, `%array_safe_set`, `%null_to_opt`, `%nullable_to_opt`), the no-op `-pp` bsc flag and unread `Clflags` fields (`-unsafe` stays accepted as an explicit no-op), and the unused `unit` slot of `Pexp_coerce`. https://github.com/rescript-lang/rescript/pull/8731
diff --git a/analysis/src/completion_front_end.ml b/analysis/src/completion_front_end.ml
index 2dbdb34b818..add09af21a6 100644
--- a/analysis/src/completion_front_end.ml
+++ b/analysis/src/completion_front_end.ml
@@ -537,7 +537,7 @@ let completion_with_parser1 ~debug ~offset ~pos_cursor ~kind_file
       scope_pattern ~pattern_path
         ?context_path:(Type_utils.context_path_from_core_type core_type)
         p
-    | Ppat_type _ -> ()
+    | Ppat_type _ | Ppat_variant_spread _ -> ()
     | Ppat_unpack {txt; loc} ->
       scope := !scope |> Scope.add_module ~name:txt ~loc
     | Ppat_exception p -> scope_pattern ~pattern_path ?context_path p
diff --git a/analysis/src/semantic_tokens.ml b/analysis/src/semantic_tokens.ml
index 4b315cfde10..0be8854d713 100644
--- a/analysis/src/semantic_tokens.ml
+++ b/analysis/src/semantic_tokens.ml
@@ -244,7 +244,7 @@ let command ~debug ~emitter ~source ~kind_file =
     | Ppat_construct (name, _) ->
       emitter |> emit_variant ~name ~debug;
       Ast_iterator.default_iterator.pat iterator p
-    | Ppat_type {txt = lid; loc} ->
+    | Ppat_type {txt = lid; loc} | Ppat_variant_spread {txt = lid; loc} ->
       emitter |> emit_type ~lid ~debug ~loc;
       Ast_iterator.default_iterator.pat iterator p
     | _ -> Ast_iterator.default_iterator.pat iterator p
diff --git a/analysis/src/utils.ml b/analysis/src/utils.ml
index 5e8298f6a74..34df53e0044 100644
--- a/analysis/src/utils.ml
+++ b/analysis/src/utils.ml
@@ -139,6 +139,7 @@ let identify_ppat pat =
   | Ppat_or _ -> "Ppat_or"
   | Ppat_constraint _ -> "Ppat_constraint"
   | Ppat_type _ -> "Ppat_type"
+  | Ppat_variant_spread _ -> "Ppat_variant_spread"
   | Ppat_unpack _ -> "Ppat_unpack"
   | Ppat_exception _ -> "Ppat_exception"
   | Ppat_extension _ -> "Ppat_extension"
diff --git a/compiler/ext/config.ml b/compiler/ext/config.ml
index 1d6ca61af8c..b7dede6436d 100644
--- a/compiler/ext/config.ml
+++ b/compiler/ext/config.ml
@@ -2,9 +2,9 @@ let cmi_magic_number = "Caml1999I035"
 
 (* Magic numbers for marshaled values of the *current* parsetree, whose layout
    changes across compiler versions. *)
-and ast_impl_magic_number = "ResImpl01312"
+and ast_impl_magic_number = "ResImpl01313"
 
-and ast_intf_magic_number = "ResIntf01312"
+and ast_intf_magic_number = "ResIntf01313"
 
 (* Magic numbers of the frozen Parsetree0 (OCaml 4.06) layout used on the
    external-PPX wire. They must never be written in front of a
diff --git a/compiler/ml/ast_helper.ml b/compiler/ml/ast_helper.ml
index 94ed0320ba1..bd0bf8b2bae 100644
--- a/compiler/ml/ast_helper.ml
+++ b/compiler/ml/ast_helper.ml
@@ -142,6 +142,7 @@ module Pat = struct
   let or_ ?loc ?attrs a b = mk ?loc ?attrs (Ppat_or (a, b))
   let constraint_ ?loc ?attrs a b = mk ?loc ?attrs (Ppat_constraint (a, b))
   let type_ ?loc ?attrs a = mk ?loc ?attrs (Ppat_type a)
+  let variant_spread ?loc ?attrs a = mk ?loc ?attrs (Ppat_variant_spread a)
   let unpack ?loc ?attrs a = mk ?loc ?attrs (Ppat_unpack a)
   let exception_ ?loc ?attrs a = mk ?loc ?attrs (Ppat_exception a)
   let extension ?loc ?attrs a = mk ?loc ?attrs (Ppat_extension a)
diff --git a/compiler/ml/ast_helper.mli b/compiler/ml/ast_helper.mli
index 701c1ed9a53..04657603f2d 100644
--- a/compiler/ml/ast_helper.mli
+++ b/compiler/ml/ast_helper.mli
@@ -107,6 +107,7 @@ module Pat : sig
   val or_ : ?loc:loc -> ?attrs:attrs -> pattern -> pattern -> pattern
   val constraint_ : ?loc:loc -> ?attrs:attrs -> pattern -> core_type -> pattern
   val type_ : ?loc:loc -> ?attrs:attrs -> lid -> pattern
+  val variant_spread : ?loc:loc -> ?attrs:attrs -> lid -> pattern
   val unpack : ?loc:loc -> ?attrs:attrs -> str -> pattern
   val exception_ : ?loc:loc -> ?attrs:attrs -> pattern -> pattern
   val extension : ?loc:loc -> ?attrs:attrs -> extension -> pattern
diff --git a/compiler/ml/ast_iterator.ml b/compiler/ml/ast_iterator.ml
index a267c8ed7c7..1459f19cf18 100644
--- a/compiler/ml/ast_iterator.ml
+++ b/compiler/ml/ast_iterator.ml
@@ -464,7 +464,7 @@ module P = struct
     | Ppat_constraint (p, t) ->
       sub.pat sub p;
       sub.typ sub t
-    | Ppat_type s -> iter_loc sub s
+    | Ppat_type s | Ppat_variant_spread s -> iter_loc sub s
     | Ppat_unpack s -> iter_loc sub s
     | Ppat_exception p -> sub.pat sub p
     | Ppat_extension x -> sub.extension sub x
diff --git a/compiler/ml/ast_mapper.ml b/compiler/ml/ast_mapper.ml
index 69a6a0152f4..a93a2e66de8 100644
--- a/compiler/ml/ast_mapper.ml
+++ b/compiler/ml/ast_mapper.ml
@@ -464,6 +464,7 @@ module P = struct
     | Ppat_constraint (p, t) ->
       constraint_ ~loc ~attrs (sub.pat sub p) (sub.typ sub t)
     | Ppat_type s -> type_ ~loc ~attrs (map_loc sub s)
+    | Ppat_variant_spread s -> variant_spread ~loc ~attrs (map_loc sub s)
     | Ppat_unpack s -> unpack ~loc ~attrs (map_loc sub s)
     | Ppat_exception p -> exception_ ~loc ~attrs (sub.pat sub p)
     | Ppat_extension x -> extension ~loc ~attrs (sub.extension sub x)
diff --git a/compiler/ml/ast_mapper_from0.ml b/compiler/ml/ast_mapper_from0.ml
index 0cd2e427bf8..38a8bed744a 100644
--- a/compiler/ml/ast_mapper_from0.ml
+++ b/compiler/ml/ast_mapper_from0.ml
@@ -44,6 +44,17 @@ let extract_internal_loc_attr attr_name attrs =
 let await_marker_loc ~node_loc (marker_loc : Location.t) =
   if marker_loc = Location.none then node_loc else marker_loc
 
+(* The [res.patVariantSpread] marker that [Ast_mapper_to0] puts on a variant
+   spread pattern, with any payload *)
+let extract_variant_spread_attr (attrs : Pt.attributes) =
+  let rec loop rev_acc = function
+    | [] -> (false, List.rev rev_acc)
+    | ({txt = "res.patVariantSpread"}, _) :: rest ->
+      (true, List.rev_append rev_acc rest)
+    | attr :: rest -> loop (attr :: rev_acc) rest
+  in
+  loop [] attrs
+
 let extract_ternary_attr (attrs : Pt.attributes) =
   let rec loop rev_acc = function
     | [] -> (false, List.rev rev_acc)
@@ -1327,7 +1338,10 @@ module P = struct
     | Ppat_or (p1, p2) -> or_ ~loc ~attrs (sub.pat sub p1) (sub.pat sub p2)
     | Ppat_constraint (p, t) ->
       constraint_ ~loc ~attrs (sub.pat sub p) (sub.typ sub t)
-    | Ppat_type s -> type_ ~loc ~attrs (map_loc sub s)
+    | Ppat_type s -> (
+      match extract_variant_spread_attr attrs with
+      | true, attrs -> variant_spread ~loc ~attrs (map_loc sub s)
+      | false, _ -> type_ ~loc ~attrs (map_loc sub s))
     | Ppat_lazy _ -> failwith "Ppat_lazy is no longer present in ReScript"
     | Ppat_unpack s -> unpack ~loc ~attrs (map_loc sub s)
     | Ppat_open _ -> failwith "Ppat_open is no longer present in ReScript"
diff --git a/compiler/ml/ast_mapper_to0.ml b/compiler/ml/ast_mapper_to0.ml
index 23329eaaf55..8c93dba9e06 100644
--- a/compiler/ml/ast_mapper_to0.ml
+++ b/compiler/ml/ast_mapper_to0.ml
@@ -907,6 +907,11 @@ module P = struct
     | Ppat_constraint (p, t) ->
       constraint_ ~loc ~attrs (sub.pat sub p) (sub.typ sub t)
     | Ppat_type s -> type_ ~loc ~attrs (map_loc sub s)
+    | Ppat_variant_spread s ->
+      (* v0 has no variant spread pattern: it's [#...t] with a marker *)
+      type_ ~loc
+        ~attrs:((Location.mknoloc "res.patVariantSpread", Pt.PStr []) :: attrs)
+        (map_loc sub s)
     | Ppat_unpack s -> unpack ~loc ~attrs (map_loc sub s)
     | Ppat_exception p -> exception_ ~loc ~attrs (sub.pat sub p)
     | Ppat_extension x -> extension ~loc ~attrs (sub.extension sub x)
diff --git a/compiler/ml/depend.ml b/compiler/ml/depend.ml
index 562165c0c9f..ad3c0761785 100644
--- a/compiler/ml/depend.ml
+++ b/compiler/ml/depend.ml
@@ -189,7 +189,7 @@ let rec add_pattern bv pat =
     add_pattern bv p;
     add_type bv ty
   | Ppat_variant (_, {txt = args}) -> List.iter (add_pattern bv) args
-  | Ppat_type li -> add bv li
+  | Ppat_type li | Ppat_variant_spread li -> add bv li
   | Ppat_unpack id -> pattern_bv := String_map.add id.txt bound !pattern_bv
   | Ppat_exception p -> add_pattern bv p
   | Ppat_extension e -> handle_extension e
diff --git a/compiler/ml/parsetree.ml b/compiler/ml/parsetree.ml
index 4c1c5bc8cd4..0297655b8e2 100644
--- a/compiler/ml/parsetree.ml
+++ b/compiler/ml/parsetree.ml
@@ -249,7 +249,8 @@ and pattern_desc =
   | Ppat_array of pattern list (* [| P1; ...; Pn |] *)
   | Ppat_or of pattern * pattern (* P1 | P2 *)
   | Ppat_constraint of pattern * core_type (* (P : T) *)
-  | Ppat_type of Longident.t loc (* #tconst *)
+  | Ppat_type of Longident.t loc (* #...tconst *)
+  | Ppat_variant_spread of Longident.t loc (* ...tconst *)
   | Ppat_unpack of string loc
     (* (module P)
        Note: (module P : S) is represented as
diff --git a/compiler/ml/pprintast.ml b/compiler/ml/pprintast.ml
index 7851338ce91..35351aa46f1 100644
--- a/compiler/ml/pprintast.ml
+++ b/compiler/ml/pprintast.ml
@@ -486,6 +486,7 @@ and simple_pattern ctxt (f : Format.formatter) (x : pattern) : unit =
     | Ppat_array l -> pp f "@[<2>[|%a|]@]" (list (pattern1 ctxt) ~sep:";") l
     | Ppat_unpack s -> pp f "(module@ %s)@ " s.txt
     | Ppat_type li -> pp f "#%a" longident_loc li
+    | Ppat_variant_spread li -> pp f "...%a" longident_loc li
     | Ppat_record (l, closed, rest) -> (
       let longident_x_pattern f {lid = li; x = p; opt} =
         let opt_str = if opt then "?" else "" in
diff --git a/compiler/ml/printast.ml b/compiler/ml/printast.ml
index 7460d90f60c..e14a6dcabb6 100644
--- a/compiler/ml/printast.ml
+++ b/compiler/ml/printast.ml
@@ -231,6 +231,9 @@ and pattern i ppf x =
   | Ppat_type li ->
     line i ppf "Ppat_type\n";
     longident_loc i ppf li
+  | Ppat_variant_spread li ->
+    line i ppf "Ppat_variant_spread\n";
+    longident_loc i ppf li
   | Ppat_unpack s -> line i ppf "Ppat_unpack %a\n" fmt_string_loc s
   | Ppat_exception p ->
     line i ppf "Ppat_exception\n";
diff --git a/compiler/ml/typecore.ml b/compiler/ml/typecore.ml
index 7f4ae21a8a1..acf4e816c3c 100644
--- a/compiler/ml/typecore.ml
+++ b/compiler/ml/typecore.ml
@@ -657,9 +657,7 @@ let extract_type_from_pat_variant_spread env lid expected_ty =
 
 let build_ppat_or_for_variant_spread pat env expected_ty =
   match pat with
-  | {ppat_desc = Ppat_type lident; ppat_attributes}
-    when Variant_coercion.has_res_pat_variant_spread_attribute ppat_attributes
-    ->
+  | {ppat_desc = Ppat_variant_spread lident} ->
     let _, _, constructors, ty =
       extract_type_from_pat_variant_spread !env lident expected_ty
     in
@@ -693,9 +691,7 @@ let build_ppat_or_for_variant_spread pat env expected_ty =
 
 let maybe_expand_variant_spread_in_pattern pattern env expected_ty =
   match pattern.Parsetree.ppat_desc with
-  | Ppat_type _
-    when Variant_coercion.has_res_pat_variant_spread_attribute
-           pattern.ppat_attributes -> (
+  | Ppat_variant_spread _ -> (
     match build_ppat_or_for_variant_spread pattern env expected_ty with
     | None -> assert false (* TODO: Fix. *)
     | Some (pattern, _) -> pattern)
@@ -1331,9 +1327,7 @@ and type_pat_aux ~constrs ~labels ~no_existentials ~mode ~explode ~env sp
   | Ppat_alias (sq, name) ->
     let override_type_from_variant_spread, sq =
       match sq with
-      | {ppat_desc = Ppat_type _; ppat_attributes}
-        when Variant_coercion.has_res_pat_variant_spread_attribute
-               ppat_attributes -> (
+      | {ppat_desc = Ppat_variant_spread _} -> (
         match build_ppat_or_for_variant_spread sq env expected_ty with
         | Some (p, ty) -> (Some ty, p)
         | None -> (None, sq))
@@ -1739,7 +1733,9 @@ and type_pat_aux ~constrs ~labels ~no_existentials ~mode ~explode ~env sp
             | _ -> {p with pat_type = ty; pat_extra = extra :: p.pat_extra}
         in
         k p)
-  | Ppat_type lid ->
+  (* [Ppat_variant_spread] is expanded above, except for a variant without
+     constructors, which is typed (and rejected) like [#...t] *)
+  | Ppat_type lid | Ppat_variant_spread lid ->
     let path, p, ty = build_or_pat !env loc lid in
     unify_pat_types loc !env ty expected_ty;
     k
@@ -2173,7 +2169,7 @@ let contains_variant_either ty =
 let iter_ppat f p =
   match p.ppat_desc with
   | Ppat_any | Ppat_var _ | Ppat_constant _ | Ppat_interval _ | Ppat_extension _
-  | Ppat_type _ | Ppat_unpack _ ->
+  | Ppat_type _ | Ppat_variant_spread _ | Ppat_unpack _ ->
     ()
   | Ppat_array pats -> List.iter f pats
   | Ppat_or (p1, p2) ->
diff --git a/compiler/ml/variant_coercion.ml b/compiler/ml/variant_coercion.ml
index 59c2052ad2e..0bd95ddbfd0 100644
--- a/compiler/ml/variant_coercion.ml
+++ b/compiler/ml/variant_coercion.ml
@@ -277,9 +277,3 @@ let type_is_variant (typ : (Path.t * Path.t * Types.type_declaration) option) =
   match typ with
   | Some (_, _, {type_kind = Type_variant _; _}) -> true
   | _ -> false
-
-let has_res_pat_variant_spread_attribute attrs =
-  attrs
-  |> List.find_opt (fun (({txt}, _) : Parsetree.attribute) ->
-      txt = "res.patVariantSpread")
-  |> Option.is_some
diff --git a/compiler/syntax/src/res_ast_debugger.ml b/compiler/syntax/src/res_ast_debugger.ml
index e3b51cdf368..dc5bc8851ae 100644
--- a/compiler/syntax/src/res_ast_debugger.ml
+++ b/compiler/syntax/src/res_ast_debugger.ml
@@ -917,6 +917,11 @@ module Sexp_ast = struct
         Sexp.list [Sexp.atom "Ppat_constraint"; pattern p; core_type typexpr]
       | Ppat_type longident_loc ->
         Sexp.list [Sexp.atom "Ppat_type"; longident longident_loc.Location.txt]
+      | Ppat_variant_spread longident_loc ->
+        Sexp.list
+          [
+            Sexp.atom "Ppat_variant_spread"; longident longident_loc.Location.txt;
+          ]
       | Ppat_unpack string_loc ->
         Sexp.list [Sexp.atom "Ppat_unpack"; string string_loc.Location.txt]
       | Ppat_exception p -> Sexp.list [Sexp.atom "Ppat_exception"; pattern p]
diff --git a/compiler/syntax/src/res_comments_table.ml b/compiler/syntax/src/res_comments_table.ml
index 1d34e711610..8aeef1ff32e 100644
--- a/compiler/syntax/src/res_comments_table.ml
+++ b/compiler/syntax/src/res_comments_table.ml
@@ -2064,7 +2064,7 @@ and walk_pattern pat t comments =
     walk_list (List.map (fun pat -> Pattern pat) pats) t rest
   | Ppat_variant (_label, {txt = args}) ->
     walk_list (List.map (fun pat -> Pattern pat) args) t comments
-  | Ppat_type _ -> ()
+  | Ppat_type _ | Ppat_variant_spread _ -> ()
   | Ppat_record (record_rows, _, rest) ->
     let nodes =
       Ext_list.map record_rows (fun {lid; x = p} -> PatternRecordRow (lid, p))
diff --git a/compiler/syntax/src/res_core.ml b/compiler/syntax/src/res_core.ml
index 4082ceca33e..799cafd0be7 100644
--- a/compiler/syntax/src/res_core.ml
+++ b/compiler/syntax/src/res_core.ml
@@ -264,8 +264,6 @@ module Error_messages = struct
     "Spreading JSX children is no longer supported."
 end
 
-let make_pat_variant_spread_attr =
-  (Location.mknoloc "res.patVariantSpread", Parsetree.PStr [])
 let spread_attr = (Location.mknoloc "res.spread", Parsetree.PStr [])
 let dict_spread_attr = (Location.mknoloc "res.dictSpread", Parsetree.PStr [])
 
@@ -1257,9 +1255,7 @@ let rec parse_pattern ?(alias = true) ?(or_ = true) p =
       Parser.next p;
       let ident = parse_value_path p in
       let loc = mk_loc start_pos ident.loc.loc_end in
-      Ast_helper.Pat.type_ ~loc
-        ~attrs:(make_pat_variant_spread_attr :: attrs)
-        ident
+      Ast_helper.Pat.variant_spread ~loc ~attrs ident
     | Hash -> (
       Parser.next p;
       if Parser.peek p == DotDotDot then (
diff --git a/compiler/syntax/src/res_parsetree_viewer.ml b/compiler/syntax/src/res_parsetree_viewer.ml
index c8a9387f109..12f22310fbd 100644
--- a/compiler/syntax/src/res_parsetree_viewer.ml
+++ b/compiler/syntax/src/res_parsetree_viewer.ml
@@ -30,13 +30,6 @@ let expr_is_await e =
   | Pexp_await _ -> true
   | _ -> false
 
-let has_res_pat_variant_spread_attribute attrs =
-  List.exists
-    (function
-      | {Location.txt = "res.patVariantSpread"}, _ -> true
-      | _ -> false)
-    attrs
-
 let has_dict_pattern_attribute attrs =
   attrs
   |> List.find_opt (fun (({txt}, _) : Parsetree.attribute) ->
@@ -221,12 +214,7 @@ let rec unwrap_braces expr =
 (* Attributes the parser adds to encode syntax; they are never printed *)
 let is_parsing_attr (attr : Parsetree.attribute) =
   match attr with
-  | ( {
-        Location.txt =
-          "res.patVariantSpread" | "res.dictPattern" | "res.dictSpread";
-      },
-      _ ) ->
-    true
+  | {Location.txt = "res.dictPattern" | "res.dictSpread"}, _ -> true
   | _ -> false
 
 let filter_parsing_attrs attrs =
diff --git a/compiler/syntax/src/res_parsetree_viewer.mli b/compiler/syntax/src/res_parsetree_viewer.mli
index b771688c181..9f4e521776e 100644
--- a/compiler/syntax/src/res_parsetree_viewer.mli
+++ b/compiler/syntax/src/res_parsetree_viewer.mli
@@ -16,7 +16,6 @@ val functor_type :
   * Parsetree.module_type
 
 val expr_is_await : Parsetree.expression -> bool
-val has_res_pat_variant_spread_attribute : Parsetree.attributes -> bool
 val has_dict_pattern_attribute : Parsetree.attributes -> bool
 
 type dict_expr_part =
diff --git a/compiler/syntax/src/res_printer.ml b/compiler/syntax/src/res_printer.ml
index c652ea29e05..12d84247be0 100644
--- a/compiler/syntax/src/res_printer.ml
+++ b/compiler/syntax/src/res_printer.ml
@@ -2827,9 +2827,7 @@ and print_pattern ~state (p : Parsetree.pattern) cmt_tbl =
       in
       let args_doc = print_pattern_args ~state variant_args cmt_tbl in
       Doc.group (Doc.concat [variant_name; args_doc])
-    | Ppat_type ident
-      when Parsetree_viewer.has_res_pat_variant_spread_attribute
-             p.ppat_attributes ->
+    | Ppat_variant_spread ident ->
       Doc.concat [Doc.text "..."; print_ident_path ident cmt_tbl]
     | Ppat_type ident ->
       Doc.concat [Doc.text "#..."; print_ident_path ident cmt_tbl]
diff --git a/tests/ounit_tests/ounit_ast_mapper0_tests.ml b/tests/ounit_tests/ounit_ast_mapper0_tests.ml
index be328ccf5b0..28746474ae1 100644
--- a/tests/ounit_tests/ounit_ast_mapper0_tests.ml
+++ b/tests/ounit_tests/ounit_ast_mapper0_tests.ml
@@ -682,6 +682,40 @@ let map_pat_to0 p =
 
 let attr_names attrs = List.map (fun ({Location.txt}, _) -> txt) attrs
 
+(* v0 has no variant spread pattern: [...t] is [#...t] with a
+   [res.patVariantSpread] marker in front of its own attributes, as the
+   parser used to produce it *)
+let test_variant_spread_pattern_through_ast0 _ =
+  let spread_loc = source_loc 2 8 in
+  let lid = located_string ~loc:(source_loc 5 8) (Longident.Lident "t") in
+  let spread =
+    Ast_helper.Pat.variant_spread ~loc:spread_loc
+      ~attrs:[attr "user" (Parsetree.PStr [])]
+      lid
+  in
+  let wire = map_pat_to0 spread in
+  (match wire.ppat_desc with
+  | Parsetree0.Ppat_type {txt = Longident.Lident "t"} -> ()
+  | _ -> assert_failure "Expected Ppat_type on the v0 wire");
+  OUnit.assert_equal ~printer:(String.concat ", ")
+    ["res.patVariantSpread"; "user"]
+    (attr_names wire.ppat_attributes);
+  (match map_pat0 wire with
+  | {
+   ppat_desc = Ppat_variant_spread {txt = Longident.Lident "t"; loc};
+   ppat_loc;
+   ppat_attributes;
+  } ->
+    OUnit.assert_equal ~msg:"pattern location" spread_loc ppat_loc;
+    OUnit.assert_equal ~msg:"type location" lid.loc loc;
+    OUnit.assert_equal ["user"] (attr_names ppat_attributes)
+  | _ -> assert_failure "Expected Ppat_variant_spread after the ast0 roundtrip");
+  (* [#...t] stays a polymorphic variant type pattern *)
+  let poly = Ast_helper.Pat.type_ ~loc lid in
+  match map_pat0 (map_pat_to0 poly) with
+  | {ppat_desc = Ppat_type _; ppat_attributes = []} -> ()
+  | _ -> assert_failure "Expected Ppat_type without attributes"
+
 let test_attributed_constructor_payloads_through_ast0 _ =
   let payload_loc = source_loc 10 30 in
   let payload_attrs = [attr "ppx.payload" (Parsetree0.PStr [])] in
@@ -1934,6 +1968,8 @@ let suites =
          >:: test_nested_awaits_are_dynamic_imports;
          "module_await_v0_attribute_order"
          >:: test_module_await_v0_attribute_order;
+         "variant_spread_pattern_through_ast0"
+         >:: test_variant_spread_pattern_through_ast0;
          "inline_record_definition_roundtrips_through_ast0"
          >:: test_inline_record_definition_roundtrips_through_ast0;
          "this_on_braced_function_reaches_builtin_ppx"
diff --git a/tests/syntax_tests/data/ast-mapping/VariantSpreadPatterns.res b/tests/syntax_tests/data/ast-mapping/VariantSpreadPatterns.res
new file mode 100644
index 00000000000..9f42ea8b8ab
--- /dev/null
+++ b/tests/syntax_tests/data/ast-mapping/VariantSpreadPatterns.res
@@ -0,0 +1,10 @@
+let f = x =>
+  switch x {
+  | ...a => 1
+  | ...a as v => v
+  | @attr ...a => 2
+  | Some(...a) => 3
+  | ...M.a | ...b => 4
+  | #...p => 5
+  | @attr #...p => 6
+  }
diff --git a/tests/syntax_tests/data/ast-mapping/expected/VariantSpreadPatterns.res.txt b/tests/syntax_tests/data/ast-mapping/expected/VariantSpreadPatterns.res.txt
new file mode 100644
index 00000000000..9f42ea8b8ab
--- /dev/null
+++ b/tests/syntax_tests/data/ast-mapping/expected/VariantSpreadPatterns.res.txt
@@ -0,0 +1,10 @@
+let f = x =>
+  switch x {
+  | ...a => 1
+  | ...a as v => v
+  | @attr ...a => 2
+  | Some(...a) => 3
+  | ...M.a | ...b => 4
+  | #...p => 5
+  | @attr #...p => 6
+  }
diff --git a/tests/syntax_tests/data/parsing/grammar/pattern/expected/variantSpreads.res.txt b/tests/syntax_tests/data/parsing/grammar/pattern/expected/variantSpreads.res.txt
index 945eafbc2b0..ecc8d54cc28 100644
--- a/tests/syntax_tests/data/parsing/grammar/pattern/expected/variantSpreads.res.txt
+++ b/tests/syntax_tests/data/parsing/grammar/pattern/expected/variantSpreads.res.txt
@@ -23,17 +23,17 @@ let doWithB [arity:1](b : b) =
    | _ -> Console.log {js|twwwoooo|js}}
 let lookup [arity:1](b : b) =
   match b with
-  | ((#a)[@res.patVariantSpread ]) as a -> doWithA a
+  | ...a as a -> doWithA a
   | Four -> Console.log {js|four|js}
   | Five -> Console.log {js|five|js}
 let lookup2 [arity:1](d : d) =
   match d with
-  | ((#a)[@res.patVariantSpread ]) as a -> doWithA a
-  | ((#b)[@res.patVariantSpread ]) as b -> doWithB b
+  | ...a as a -> doWithA a
+  | ...b as b -> doWithB b
   | Six|Seven -> Console.log {js|Got rest of d|js}
 let lookupOpt [arity:1](b : b option) =
   match b with
-  | Some (((#a)[@res.patVariantSpread ]) as a) -> doWithA a
+  | Some (...a as a) -> doWithA a
   | Some (Four) -> Console.log {js|four|js}
   | Some (Five) -> Console.log {js|five|js}
   | None -> Console.log {js|None|js}
@@ -52,5 +52,5 @@ let doWithZ [arity:1](z : Foo.zz) =
   | Second -> Console.log {js|Second|js}
 let lookup3 [arity:1](d : Foo.xx) =
   match d with
-  | ((#Foo.zz)[@res.patVariantSpread ]) as z -> Console.log z
+  | ...Foo.zz as z -> Console.log z
   | Third -> Console.log {js|Third|js}
\ No newline at end of file

From 30d64b5abe4dd4dc6fa69bd253570df1f2d6cd52 Mon Sep 17 00:00:00 2001
From: Christoph Knittel <ck@cca.io>
Date: Thu, 8 Oct 2026 17:51:21 +0000
Subject: [PATCH 2/2] Add CHANGELOG link for #8742

Signed-off-by: Christoph Knittel <christoph@knittel.cc>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
---
 CHANGELOG.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0e66a867b54..d3bacc2ab6f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -48,7 +48,7 @@
 #### :house: Internal
 
 - Remove the unused `res.iflet` encoding of `if let`, which the parser always rejects with a syntax error suggesting a `switch`. The error is unchanged. https://github.com/rescript-lang/rescript/pull/8741
-- Represent variant spread patterns (`...t`) with a dedicated `Ppat_variant_spread` parsetree node instead of `Ppat_type` with a `res.patVariantSpread` attribute, which remains only in the PPX wire representation. PR_LINK
+- Represent variant spread patterns (`...t`) with a dedicated `Ppat_variant_spread` parsetree node instead of `Ppat_type` with a `res.patVariantSpread` attribute, which remains only in the PPX wire representation. https://github.com/rescript-lang/rescript/pull/8742
 - Remove the obsolete `res.ternary` and `JSX` attributes from the formatter's internal attribute filters and merge the filters into one. https://github.com/rescript-lang/rescript/pull/8740
 - Represent `await` on module expressions with a dedicated `Pmod_await` parsetree node instead of a `res.await` attribute, which remains only in the PPX wire representation. https://github.com/rescript-lang/rescript/pull/8738
 - Remove dead compiler code: warning 24, the `J.String_index` JS IR node, the `Pisint` and `Parraysets` Lambda primitives with their unused `%` primitive names (`%obj_is_int`, `%obj_dup`, `%obj_field`, `%array_safe_set`, `%null_to_opt`, `%nullable_to_opt`), the no-op `-pp` bsc flag and unread `Clflags` fields (`-unsafe` stays accepted as an explicit no-op), and the unused `unit` slot of `Pexp_coerce`. https://github.com/rescript-lang/rescript/pull/8731