src: use single ObjectTemplate for TextDecoder

`ObjectTemplate`s are not garbage-collected like regular objects
(for some reason). It is sufficient to create a single template
anyway, so do that to address the memory leak.

Fixes: #32424

PR-URL: #32426
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: addaleax

src/env.h

@@ -412,6 +412,7 @@ constexpr size_t kFsStatsBufferLength =
   V(http2settings_constructor_template, v8::ObjectTemplate)                    \
   V(http2stream_constructor_template, v8::ObjectTemplate)                      \
   V(http2ping_constructor_template, v8::ObjectTemplate)                        \
+  V(i18n_converter_template, v8::ObjectTemplate)                               \
   V(libuv_stream_wrap_ctor_template, v8::FunctionTemplate)                     \
   V(message_port_constructor_template, v8::FunctionTemplate)                   \
   V(pipe_constructor_template, v8::FunctionTemplate)                           \

src/node_i18n.cc

@@ -86,6 +86,7 @@ namespace node {
 
 using v8::Context;
 using v8::FunctionCallbackInfo;
+using v8::FunctionTemplate;
 using v8::HandleScope;
 using v8::Int32;
 using v8::Isolate;
@@ -171,8 +172,7 @@ class ConverterObject : public BaseObject, Converter {
     Environment* env = Environment::GetCurrent(args);
     HandleScope scope(env->isolate());
 
-    Local<ObjectTemplate> t = ObjectTemplate::New(env->isolate());
-    t->SetInternalFieldCount(ConverterObject::kInternalFieldCount);
+    Local<ObjectTemplate> t = env->i18n_converter_template();
     Local<Object> obj;
     if (!t->NewInstance(env->context()).ToLocal(&obj)) return;
 
@@ -821,6 +821,16 @@ void Initialize(Local<Object> target,
   env->SetMethod(target, "transcode", Transcode);
 
   // ConverterObject
+  {
+    Local<FunctionTemplate> t = FunctionTemplate::New(env->isolate());
+    t->InstanceTemplate()->SetInternalFieldCount(
+        ConverterObject::kInternalFieldCount);
+    Local<String> converter_string =
+        FIXED_ONE_BYTE_STRING(env->isolate(), "Converter");
+    t->SetClassName(converter_string);
+    env->set_i18n_converter_template(t->InstanceTemplate());
+  }
+
   env->SetMethod(target, "getConverter", ConverterObject::Create);
   env->SetMethod(target, "decode", ConverterObject::Decode);
   env->SetMethod(target, "hasConverter", ConverterObject::Has);

test/parallel/test-whatwg-encoding-custom-textdecoder.js

@@ -107,8 +107,13 @@ if (common.hasIntl) {
   if (common.hasIntl) {
     assert.strictEqual(
       util.inspect(dec, { showHidden: true }),
-      'TextDecoder {\n  encoding: \'utf-8\',\n  fatal: false,\n  ' +
-      'ignoreBOM: true,\n  [Symbol(flags)]: 4,\n  [Symbol(handle)]: {}\n}'
+      'TextDecoder {\n' +
+      '  encoding: \'utf-8\',\n' +
+      '  fatal: false,\n' +
+      '  ignoreBOM: true,\n' +
+      '  [Symbol(flags)]: 4,\n' +
+      '  [Symbol(handle)]: Converter {}\n' +
+      '}'
     );
   } else {
     assert.strictEqual(