[strong] Class constructor bodies cannot contain "use strong" directive

src/preparser.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include <cmath>
 
 #include "src/allocation.h"
 #include "src/base/logging.h"
 #include "src/conversions-inl.h"
 #include "src/conversions.h"
@@ skipping 244 matching lines @@
       bool use_strict_found = statement.IsUseStrictLiteral();
       bool use_strong_found =
           statement.IsUseStrongLiteral() && allow_strong_mode();
 
       if (use_strict_found) {
         scope_->SetLanguageMode(
             static_cast<LanguageMode>(scope_->language_mode() | STRICT));
       } else if (use_strong_found) {
         scope_->SetLanguageMode(static_cast<LanguageMode>(
             scope_->language_mode() | STRONG));
+        if (i::IsConstructor(function_state_->kind())) {
+          // "use strong" cannot occur in a class constructor body, to avoid
+          // unintuitive strong class object semantics.
+          PreParserTraits::ReportMessageAt(
+              token_loc, MessageTemplate::kStrongConstructorDirective);
+          *ok = false;
+          return;
+        }
       } else if (!statement.IsStringLiteral()) {
         directive_prologue = false;
       }
 
       if ((use_strict_found || use_strong_found) &&
           !scope_->HasSimpleParameters()) {
         // TC39 deemed "use strict" directives to be an error when occurring
         // in the body of a function with non-simple parameter list, on
         // 29/7/2015. https://goo.gl/ueA7Ln
         //
@@ skipping 948 matching lines @@
 
   DCHECK(!spread_pos.IsValid());
 
   return Expression::Default();
 }
 
 #undef CHECK_OK
 
 
 } }  // v8::internal