bindings: Support sequence in callback function arguments

third_party/WebKit/Source/bindings/templates/callback_function.cpp

 {% from 'utilities.cpp' import v8_value_to_local_cpp_value %}
 {% filter format_blink_cpp_source_code %}
 
 {% include 'copyright_block.txt' %}
 
 #include "{{v8_class}}.h"
 
 {% for filename in cpp_includes %}
 #include "{{filename}}"
 {% endfor %}
@@ skipping 11 matching lines @@
 {
 }
 
 bool {{v8_class}}::call({{argument_declarations | join(', ')}})
 {
     if (!scriptState->contextIsValid())
         return false;
 
     if (m_callback.isEmpty())
         return false;
+
     ScriptState::Scope scope(scriptState);
+    ExceptionState exceptionState(scriptState->isolate(), ExceptionState::ExecutionContext, "{{cpp_class}}");

[bashi, 2016/09/21 02:00:21]

Always declare exceptionState for simplicity.

Another option would be passing exceptionState to call(). Maybe this approach is
more reasonable but number of arguments increases. WDYT? I don't have strong
opinion here.

[peria, 2016/09/21 02:21:36]

+1 to declare it here.

[haraken, 2016/09/21 02:25:12]

What is an expected behavior when an exception is thrown to the ExceptionState?

IIUC an expected behavior would be just to suppress the exception (c.f., we have
the v8::TryCatch block at line 47). If that is the case, we'll need to put the
ExceptionState inside the v8::TryCatch block.

[bashi, 2016/09/21 05:01:45]

Hmm, glanced at existing hand-written callbacks and it seems there are three
cases:
1. suppress exceptions (like this template)
2. rethrow exceptions (CustomElementCallback)
3. Don't use TryCatch (IDBObserverCallback)

Maybe the right behavior is:
- Pass ExceptionState
- Use TryCatch inside call()
- ExceptionState::rethrowV8Exception() when V8ScriptRunner::callFunction() fails
- Callers may call ExceptionState::clearException()

?

[Yuki, 2016/09/21 07:59:37]

Yes, I think that's the expected design.
Always killing an exception is wrong.  (But l-g-t-m'ed because I thought it's
okay as the first step.)

In general, I think an owner of this callback function object should be
responsible for everything (e.g. lifetime, exception handling) except for
invoking a callback function.

 
     {% for argument in arguments %}
     v8::Local<v8::Value> {{argument.argument_name}} = {{argument.cpp_value_to_v8_value}};
     {% endfor %}
     {% if arguments %}
     v8::Local<v8::Value> argv[] = { {{arguments | join(', ', 'argument_name')}} };
     {% else %}
     {# Empty array initializers are illegal, and don\'t compile in MSVC. #}
     v8::Local<v8::Value> *argv = nullptr;
     {% endif %}
 
     v8::Local<v8::Value> v8ReturnValue;
     v8::TryCatch exceptionCatcher(scriptState->isolate());
     exceptionCatcher.SetVerbose(true);
 
     if (V8ScriptRunner::callFunction(m_callback.newLocal(scriptState->isolate()), scriptState->getExecutionContext(), scriptState->context()->Global(), {{arguments | length}}, argv, scriptState->isolate()).ToLocal(&v8ReturnValue))
     {
         {% if return_value %}
         {{v8_value_to_local_cpp_value(return_value) | indent(8)}}
         returnValue = cppValue;
         {% endif %}
         return true;
     }
     return false;
 }
 
 } // namespace blink
 
 {% endfilter %}{# format_blink_cpp_source_code #}