binidngs: Make callInternalFunction return MaybeLocal

Source/bindings/core/v8/ScriptRegexp.cpp

 /*
  * Copyright (C) 2004, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Collabora Ltd.
  * Copyright (C) 2011 Peter Varga (pvarga@webkit.org), University of Szeged
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
@@ skipping 60 matching lines @@
     ScriptForbiddenScope::AllowUserAgentScript allowScript;
 
     v8::Isolate* isolate = v8::Isolate::GetCurrent();
     v8::HandleScope handleScope(isolate);
     v8::Context::Scope contextScope(V8PerIsolateData::from(isolate)->ensureScriptRegexpContext());
     v8::TryCatch tryCatch;
 
     v8::Local<v8::RegExp> regex = m_regex.newLocal(isolate);
     v8::Local<v8::Function> exec = regex->Get(v8AtomicString(isolate, "exec")).As<v8::Function>();
     v8::Local<v8::Value> argv[] = { v8String(isolate, string.substring(startFrom)) };
-    v8::Local<v8::Value> returnValue = V8ScriptRunner::callInternalFunction(exec, regex, WTF_ARRAY_LENGTH(argv), argv, isolate);
-
-    if (tryCatch.HasCaught())
+    v8::Local<v8::Value> returnValue;
+    if (!V8ScriptRunner::callInternalFunction(exec, regex, WTF_ARRAY_LENGTH(argv), argv, isolate).ToLocal(&returnValue))

[yurys, 2015/03/25 12:21:48]

I don't quite understand what's the advantage of returning MaybeLocal(which will
in most cases be followed by ToLocal) compared to calling IsEmpty() on the
result handle, can you please explain? Given that users can end up with an empty
Local handle after calling ToLocal I don't see a big improvement over inserting
IsEmpty() checks at all places where we get Local handle. Is it just to help
find all places where Local handle is used in potentially exception unsafe
manner?

         return -1;
 
     // RegExp#exec returns null if there's no match, otherwise it returns an
     // Array of strings with the first being the whole match string and others
     // being subgroups. The Array also has some random properties tacked on like
     // "index" which is the offset of the match.
     //
     // https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/RegExp/exec
 
     ASSERT(!returnValue.IsEmpty());
     if (!returnValue->IsArray())
         return -1;
 
     v8::Local<v8::Array> result = returnValue.As<v8::Array>();
     int matchOffset = result->Get(v8AtomicString(isolate, "index"))->ToInt32(isolate)->Value();
     if (matchLength) {
         v8::Local<v8::String> match = result->Get(0).As<v8::String>();
         *matchLength = match->Length();
     }
 
     return matchOffset + startFrom;
 }
 
 } // namespace blink