src: constrain COW forwarding constructors

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)...)) {}
 

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) {