Issue 6526 - *ToV8String() return MaybeLocal<> and check Call() return value

src/Utils.cpp

Index: src/Utils.cpp
===================================================================
--- a/src/Utils.cpp
+++ b/src/Utils.cpp
@@ -45,32 +45,39 @@
 {
   v8::String::Utf8Value stringValue(isolate, value);
   if (stringValue.length())
     return IFileSystem::IOBuffer(*stringValue, *stringValue + stringValue.length());
   else
     return IFileSystem::IOBuffer();
 }
 
-v8::Local<v8::String> Utils::ToV8String(v8::Isolate* isolate, const std::string& str)
+v8::MaybeLocal<v8::String> Utils::ToV8String(v8::Isolate* isolate, const std::string& str)
 {
   return v8::String::NewFromUtf8(isolate, str.c_str(),
-    v8::String::NewStringType::kNormalString, str.length());
+    v8::NewStringType::kNormal, str.length());
 }
 
-v8::Local<v8::String> Utils::StringBufferToV8String(v8::Isolate* isolate, const StringBuffer& str)
+v8::MaybeLocal<v8::String> Utils::StringBufferToV8String(v8::Isolate* isolate, const StringBuffer& str)
 {
   return v8::String::NewFromUtf8(isolate,
     reinterpret_cast<const char*>(str.data()),
-    v8::String::NewStringType::kNormalString, str.size());
+    v8::NewStringType::kNormal, str.size());
 }
 
 void Utils::ThrowExceptionInJS(v8::Isolate* isolate, const std::string& str)
 {
-  isolate->ThrowException(Utils::ToV8String(isolate, str));
+  auto maybe = Utils::ToV8String(isolate, str);
+  if (maybe.IsEmpty())
+  {
+    isolate->ThrowException(
+      Utils::ToV8String(isolate, "Unknown Exception").ToLocalChecked());

[hub, 2018/06/22 00:34:31]

Failure throwing an exception. Not good. So at least we should be fine. Note
that since I pass a plain ASCII string, I expect the Maybe<> to not be empty. I
believe the assumption is correct.

[sergei, 2018/06/22 06:57:46]

I'm not sure how it works. Can we create a couple of tests for that?
The first test should call TerminateExecution and then try to
Utils::ThrowExceptionInJS.
The second one should cause the stack overflow and then try to
Utils::ThrowExceptionInJS.

[hub, 2018/06/22 15:50:56]

Right now, the gist is that if we can't obtain the UTF-8 then we have a default
string and still throw an exception. NewFromUtf8() will only return empty if
length is too large.

[sergei, 2018/07/05 08:39:00]

But it can be changed later and it can start to return an empty value if someone
called `TerminateExecution` from another thread.

+  }
+  else
+    isolate->ThrowException(maybe.ToLocalChecked());
 }
 
 #ifdef _WIN32
 std::wstring Utils::ToUtf16String(const std::string& str)
 {
   size_t length = str.size();
   if (length == 0)
     return std::wstring();