From 2ed4a638f46c771672f248ffaff844e35b4d41bf Mon Sep 17 00:00:00 2001
From: Thomas Lively <tlively@google.com>
Date: Mon, 11 May 2026 10:07:10 -0700
Subject: [PATCH] Make cont.new a constant expression

Document this in Explainer.md, update the interpreter, and add tests. Remove a runtime type check during global allocation that incorrectly fails for globals holding continuations because continuations do not contain runtime type information.

Closes #145.
---
 interpreter/runtime/global.ml           |  1 -
 interpreter/valid/valid.ml              |  2 +-
 proposals/stack-switching/Explainer.md  |  6 +++-
 test/core/stack-switching/cont.new.wast | 39 ++++++++++++-------------
 4 files changed, 24 insertions(+), 24 deletions(-)

diff --git a/interpreter/runtime/global.ml b/interpreter/runtime/global.ml
index cf69d2ac..8775976f 100644
--- a/interpreter/runtime/global.ml
+++ b/interpreter/runtime/global.ml
@@ -9,7 +9,6 @@ exception NotMutable
 
 let alloc (GlobalT (_mut, t) as ty) v =
   assert Free.((val_type t).types = Set.empty);
-  if not (Match.match_val_type [] (type_of_value v) t) then raise Type;
   {ty; content = v}
 
 let type_of glob =
diff --git a/interpreter/valid/valid.ml b/interpreter/valid/valid.ml
index aa6621ce..0cca2f22 100644
--- a/interpreter/valid/valid.ml
+++ b/interpreter/valid/valid.ml
@@ -1147,7 +1147,7 @@ let is_const (c : context) (e : instr) =
   | Const _ | VecConst _
   | Binary (Value.I32 I32Op.(Add | Sub | Mul))
   | Binary (Value.I64 I64Op.(Add | Sub | Mul))
-  | RefNull _ | RefFunc _
+  | RefNull _ | RefFunc _ | ContNew _
   | RefI31 | StructNew _ | ArrayNew _ | ArrayNewFixed _ -> true
   | GlobalGet x -> let GlobalT (mut, _t) = global c x in mut = Cons
   | _ -> false
diff --git a/proposals/stack-switching/Explainer.md b/proposals/stack-switching/Explainer.md
index f370591c..d2196dbf 100644
--- a/proposals/stack-switching/Explainer.md
+++ b/proposals/stack-switching/Explainer.md
@@ -550,7 +550,8 @@ function.
 ```
 
 It takes a reference to a function of type `[t1*] -> [t2*]` whose body
-may perform non-local control flow.
+may perform non-local control flow. `cont.new` is a constant
+expression, so it can be used in places like global initializers.
 
 ### Invoking continuations
 
@@ -1035,6 +1036,9 @@ where `rt` is the respective target type of the cast instruction, and the `casta
 - `rt castable`
   - iff not (rt <: (ref null cont))
 
+
+Finally, `cont.new` is added to the set of constant expressions.
+
 ### Execution
 
 The same control tag may be used simultaneously by `throw`, `suspend`,
diff --git a/test/core/stack-switching/cont.new.wast b/test/core/stack-switching/cont.new.wast
index 4e17fec5..a843577d 100644
--- a/test/core/stack-switching/cont.new.wast
+++ b/test/core/stack-switching/cont.new.wast
@@ -322,24 +322,21 @@
   "type mismatch"
 )
 
-;; TODO: Make cont.new constant
-;; https://github.com/WebAssembly/stack-switching/issues/145
-
-;; ;; Constant expression in global definition.
-;; (module
-;;   (type $f (func))
-;;   (type $k (cont $f))
-;;   (global $k (export "k") (ref $k) (cont.new $k (ref.func $f)))
-;;   (func $f (type $f))
-;; )
-;; (assert_return (get "k") (ref.cont))
-
-;; ;; Constant expression in element segment definition.
-;; (module
-;;   (type $f (func))
-;;   (type $k (cont $f))
-;;   (table $t (ref null $k) (elem (cont.new $k (ref.func $f))))
-;;   (func $f (type $f))
-;;   (func (export "get") (result (ref null $k)) (table.get $t (i32.const 0)))
-;; )
-;; (assert_return (invoke "get") (ref.cont))
+;; Constant expression in global definition.
+(module
+  (type $f (func))
+  (type $k (cont $f))
+  (global $k (export "k") (ref $k) (cont.new $k (ref.func $f)))
+  (func $f (type $f))
+)
+(assert_return (get "k") (ref.cont))
+
+;; Constant expression in element segment definition.
+(module
+  (type $f (func))
+  (type $k (cont $f))
+  (table $t (ref null $k) (elem (cont.new $k (ref.func $f))))
+  (func $f (type $f))
+  (func (export "get") (result (ref null $k)) (table.get $t (i32.const 0)))
+)
+(assert_return (invoke "get") (ref.cont))