From efc5fa99a24ffa0877063b051787978e34d25cfc Mon Sep 17 00:00:00 2001
From: Archkon <180910180+Archkon@users.noreply.github.com>
Date: Fri, 31 Jul 2026 12:06:40 +0800
Subject: [PATCH] src: constrain COW forwarding constructors

Exclude the wrapper type from the forwarding constructors so that
non-const lvalue copies select the copy constructor.

Signed-off-by: Archkon <180910180+Archkon@users.noreply.github.com>
---
 src/node_threadsafe_cow.h       | 10 +++++++++-
 test/cctest/test_per_process.cc | 22 ++++++++++++++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/node_threadsafe_cow.h b/src/node_threadsafe_cow.h
index 8cfdd006b12f..4d823b23f59d 100644
--- a/src/node_threadsafe_cow.h
+++ b/src/node_threadsafe_cow.h
@@ -6,7 +6,9 @@
 #include "util.h"
 #include "uv.h"
 
-#include <memory>   // std::shared_ptr<T>
+#include <concepts>
+#include <memory>  // std::shared_ptr<T>
+#include <type_traits>
 #include <utility>  // std::forward<T>
 
 namespace node {
@@ -17,6 +19,8 @@ template <typename T>
 class CopyOnWrite final {
  public:
   template <typename... Args>
+    requires(!(sizeof...(Args) == 1 &&
+               (std::same_as<CopyOnWrite, std::remove_cvref_t<Args>> || ...)))
   explicit CopyOnWrite(Args&&... args)
       : data_(std::make_shared<T>(std::forward<Args>(args)...)) {}
 
@@ -57,6 +61,10 @@ class ThreadsafeCopyOnWrite final {
 
  public:
   template <typename... Args>
+    requires(
+        !(sizeof...(Args) == 1 &&
+          (std::same_as<ThreadsafeCopyOnWrite, std::remove_cvref_t<Args>> ||
+           ...)))
   ThreadsafeCopyOnWrite(Args&&... args)
       : impl_(T(std::forward<Args>(args)...)) {}
 
diff --git a/test/cctest/test_per_process.cc b/test/cctest/test_per_process.cc
index 7a6f53d56222..dce250e18f8d 100644
--- a/test/cctest/test_per_process.cc
+++ b/test/cctest/test_per_process.cc
@@ -6,6 +6,8 @@
 
 #include <string>
 
+using node::CopyOnWrite;
+using node::ThreadsafeCopyOnWrite;
 using node::builtins::BuiltinLoader;
 using node::builtins::BuiltinSourceMap;
 
@@ -18,6 +20,26 @@ class PerProcessTest : public ::testing::Test {
 
 namespace {
 
+TEST(CopyOnWriteTest, CopiesFromNonConstLvalue) {
+  CopyOnWrite<int> original(42);
+  CopyOnWrite<int> copy(original);
+
+  *copy.write() = 43;
+
+  EXPECT_EQ(*original, 42);
+  EXPECT_EQ(*copy, 43);
+}
+
+TEST(ThreadsafeCopyOnWriteTest, CopiesFromNonConstLvalue) {
+  ThreadsafeCopyOnWrite<int> original(42);
+  ThreadsafeCopyOnWrite<int> copy(original);
+
+  *copy.write() = 43;
+
+  EXPECT_EQ(*original.read(), 42);
+  EXPECT_EQ(*copy.read(), 43);
+}
+
 TEST_F(PerProcessTest, EmbeddedSources) {
   const auto& sources = PerProcessTest::get_sources_for_test();
   ASSERT_TRUE(std::any_of(sources.cbegin(), sources.cend(), [](auto p) {