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)
+  /*
+   * Check that a Maybe<> isn't empty, and throw a JsValueError if it is.
+   * Call using the macro %CHECK_MAYBE to get the location.
+   */
+  template<class T>
+  void CheckMaybe(v8::Isolate* isolate, const v8::MaybeLocal<T>& value,
+                  const char* filename, int line)
   {
-    if (tryCatch.HasCaught())
-      throw AdblockPlus::JsError(isolate,
-                                 tryCatch.Exception(), tryCatch.Message());
+    if (value.IsEmpty())
+      throw AdblockPlus::JsError("Empty value at ", filename, line);
   }
 
+#define CHECK_MAYBE(isolate, value) \
+  CheckMaybe(isolate, value, __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 126 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);
   const v8::TryCatch tryCatch(GetIsolate());
-  const v8::Local<v8::Script> script = CompileScript(GetIsolate(), source,
+  v8::MaybeLocal<v8::Script> script = CompileScript(GetIsolate(), source,
     filename);
-  CheckTryCatch(GetIsolate(), tryCatch);
-  v8::Local<v8::Value> result = script->Run();
-  CheckTryCatch(GetIsolate(), tryCatch);
-  return JsValue(shared_from_this(), result);
+  CHECK_MAYBE(GetIsolate(), script);
+  v8::MaybeLocal<v8::Value> result = script.ToLocalChecked()->Run(
+    GetIsolate()->GetCurrentContext());
+  CHECK_MAYBE(GetIsolate(), result);
+  return JsValue(shared_from_this(), result.ToLocalChecked());

[sergei, 2018/06/20 15:09:55]

I think it's very important to keep the exception if there were some. It helped
me several times, so I would propose to not remove the call
`CheckTryCatch(GetIsolate(), tryCatch);`.

What do you think about something like

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

where CheckedToLocal is perhaps a template function, we can elaborate here
later, BTW
template<typename T>
v8::Local<T> CheckedToLocal(tryCatch, value, filename, line)
{
  CheckTryCatch(GetIsolate(), tryCatch);
  if (value.IsEmpty()) // here could even use V8_UNLIKELY
    throw AdblockPlus::JsError("Empty value at ", filename, line);
  return value.ToLocalChecked();
}
(the macro with __FILE__, __LINE__ is omitted).

[hub, 2018/06/20 16:09:21]

Done.

 }
 
 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);
 }