Issue 6526 - Use the maybe version of Compile() and Run()

src/JsEngine.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include <AdblockPlus.h>
 #include "GlobalJsObject.h"
 #include "JsContext.h"
 #include "JsError.h"
 #include "Utils.h"
 #include <libplatform/libplatform.h>
 #include <AdblockPlus/Platform.h>
 
 namespace
 {
-  v8::Local<v8::Script> CompileScript(v8::Isolate* isolate,
+  v8::MaybeLocal<v8::Script> CompileScript(v8::Isolate* isolate,
     const std::string& source, const std::string& filename)
   {
     using AdblockPlus::Utils::ToV8String;
     const v8::Local<v8::String> v8Source = ToV8String(isolate, source);
     if (filename.length())
     {
       const v8::Local<v8::String> v8Filename = ToV8String(isolate, filename);
-      return v8::Script::Compile(v8Source, v8Filename);
+      v8::ScriptOrigin scriptOrigin(v8Filename);
+      return v8::Script::Compile(isolate->GetCurrentContext(), v8Source, &scriptOrigin);
     }
     else
-      return v8::Script::Compile(v8Source);
+      return v8::Script::Compile(isolate->GetCurrentContext(), v8Source);
   }
 
   void CheckTryCatch(v8::Isolate* isolate, const v8::TryCatch& tryCatch)
   {
     if (tryCatch.HasCaught())
       throw AdblockPlus::JsError(isolate, tryCatch.Exception(), tryCatch.Message());
   }
 
+  /*
+   * Check for exception and then that a MaybeLocal<> isn't empty,
+   * and throw a JsError if it is, otherwise return the Local<>
+   * Call using the macro %CHECKED_MAYBE to get the location.
+   */
+  template<class T>
+  v8::Local<T> CheckedToLocal(v8::Isolate* isolate, v8::MaybeLocal<T>& value,
+                  const v8::TryCatch& tryCatch, const char* filename, int line)
+  {
+    CheckTryCatch(isolate, tryCatch);
+    if (value.IsEmpty())
+      throw AdblockPlus::JsError("Empty value at ", filename, line);
+    return value.ToLocalChecked();
+  }
+
+#define CHECKED_TO_LOCAL(isolate, value, tryCatch) \
+  CheckedToLocal(isolate, value, tryCatch, __FILE__, __LINE__)
+
   class V8Initializer
   {
     V8Initializer()
       : platform{nullptr}
     {
       std::string cmd = "--use_strict";
       v8::V8::SetFlagsFromString(cmd.c_str(), cmd.length());
       platform = v8::platform::CreateDefaultPlatform();
       v8::V8::InitializePlatform(platform);
       v8::V8::Initialize();
@@ skipping 127 matching lines @@
   JsContext context(*this);
   return JsValue(shared_from_this(), context.GetV8Context()->Global());
 }
 
 AdblockPlus::JsValue AdblockPlus::JsEngine::Evaluate(const std::string& source,
     const std::string& filename)
 {
   const JsContext context(*this);
   auto isolate = GetIsolate();
   const v8::TryCatch tryCatch(isolate);
-  const v8::Local<v8::Script> script = CompileScript(isolate, source,
+  v8::MaybeLocal<v8::Script> script = CompileScript(isolate, source,

[sergei, 2018/06/20 16:32:59]

what do you think about calling CHECKED_TO_LOCAL and don't use local variables
of v8::MaybeLocal type?

[hub, 2018/06/20 16:41:47]

I can't. CheckedToLocal() 2nd argument is expected to be an l-value.

[sergei, 2018/06/20 19:01:50]

Can the argument be r-value, v8::MaybeLocal<T>&& value?

[hub, 2018/06/21 01:13:43]

Yes.
But I don't find the result very readable. And I don't think it change anything.
Here is what it looks like:


  const JsContext context(*this);
  auto isolate = GetIsolate();
  const v8::TryCatch tryCatch(isolate);
  return JsValue(
    shared_from_this(),
    CHECKED_TO_LOCAL(
      isolate,
      CHECKED_TO_LOCAL(
        isolate,
        CompileScript(isolate, source, filename),
        tryCatch
      )->Run(isolate->GetCurrentContext()),
      tryCatch));

[sergei, 2018/06/21 08:45:45]

If one has to use the variable more than one time then there will be several
calls of CHECKED_TO_LOCAL for the same variable. This is also readable.

auto script = CHECKED_TO_LOCAL(isolate, CompileScript(isolate, source,
filename), tryCatch);
auto result = CHECKED_TO_LOCAL(isolate,
script->Run(isolate->GetCurrentContext()), tryCatch);
return JsValue(shared_from_this(), result);

[hub, 2018/06/21 13:02:17]

Done.

     filename);
-  CheckTryCatch(isolate, tryCatch);
-  v8::Local<v8::Value> result = script->Run();
-  CheckTryCatch(isolate, tryCatch);
-  return JsValue(shared_from_this(), result);
+  v8::MaybeLocal<v8::Value> result = CHECKED_TO_LOCAL(
+    isolate, script, tryCatch)->Run(isolate->GetCurrentContext());
+  return JsValue(shared_from_this(), CHECKED_TO_LOCAL(isolate, result, tryCatch));
 }
 
 void AdblockPlus::JsEngine::SetEventCallback(const std::string& eventName,
     const AdblockPlus::JsEngine::EventCallback& callback)
 {
   if (!callback)
   {
     RemoveEventCallback(eventName);
     return;
   }
@@ skipping 130 matching lines @@
     list.push_back(JsValue(shared_from_this(), arguments[i]));
   return list;
 }
 
 void AdblockPlus::JsEngine::SetGlobalProperty(const std::string& name,
                                               const AdblockPlus::JsValue& value)
 {
   auto global = GetGlobalObject();
   global.SetProperty(name, value);
 }