Create fewer local v8::TryCatch objects in generated bindings code

Source/bindings/templates/methods.cpp

 {##############################################################################}
 {% macro generate_method(method, world_suffix) %}
 {% filter conditional(method.conditional_string) %}
 static void {{method.name}}{{method.overload_index}}Method{{world_suffix}}(const v8::FunctionCallbackInfo<v8::Value>& info)
 {
     {# Local variables #}
     {% if method.has_exception_state %}
     ExceptionState exceptionState(ExceptionState::ExecutionContext, "{{method.name}}", "{{interface_name}}", info.Holder(), info.GetIsolate());
     {% endif %}
     {% if method.number_of_required_arguments %}
@@ skipping 26 matching lines @@
     }
     {% endif %}
     {% if method.is_check_security_for_node %}
     if (!BindingSecurity::shouldAllowAccessToNode(info.GetIsolate(), impl->{{method.name}}(exceptionState), exceptionState)) {
         v8SetReturnValueNull(info);
         exceptionState.throwIfNeeded();
         return;
     }
     {% endif %}
     {# Call method #}
-    {% for argument in method.arguments %}
-    {{generate_argument(method, argument, world_suffix) | indent}}
-    {% endfor %}
+    {% if method.arguments %}
+    {{generate_arguments(method, world_suffix) | indent}}
+    {% endif %}
     {% if world_suffix %}
     {{cpp_method_call(method, method.v8_set_return_value_for_main_world, method.cpp_value) | indent}}
     {% else %}
     {{cpp_method_call(method, method.v8_set_return_value, method.cpp_value) | indent}}
     {% endif %}
     {# Post-call #}
     {% if method.has_event_listener_argument %}
     {{hidden_dependency_action(method.name) | indent}}
     {% endif %}
 }
 {% endfilter %}
 {% endmacro %}
 
 
 {######################################}
 {% macro hidden_dependency_action(method_name) %}
 if (listener && !impl->toNode())
     {% if method_name == 'addEventListener' %}
     addHiddenValueToArray(info.Holder(), info[1], {{v8_class}}::eventListenerCacheIndex, info.GetIsolate());
     {% else %}{# method_name == 'removeEventListener' #}
     removeHiddenValueFromArray(info.Holder(), info[1], {{v8_class}}::eventListenerCacheIndex, info.GetIsolate());
     {% endif %}
 {% endmacro %}
 
 
 {######################################}

[Nils Barth (inactive), 2014/05/07 03:02:19]

Could you rename this as
generate_argument_var_declaration
(or, if you prefer, *var_definition, which is slightly more correct)
...to make it explicit?

+{% macro generate_argument_var(argument) %}

[Nils Barth (inactive), 2014/05/07 03:02:19]

This is a one-line macro, so please put the ; at the call site and strip
trailing newlines (using {%- ).

This is a bit confusing, so it's detailed at the style guide:
http://dev.chromium.org/developers/jinja
at:
Treat one-line macros as in-line (no indent, {%- to strip trailing linebreak,
semicolon ; at call site)
http://dev.chromium.org/developers/jinja#TOC-Treat-one-line-macros-as-in-line...

[Jens Widell, 2014/05/07 10:34:46]

Thanks for the pointers! The white-space handling was a bit confusing,
especially before I discovered the {%- modifier.

[Nils Barth (inactive), 2014/05/08 00:55:13]

Jinja whitespace handling was the bane of my life for a while (>.<)
...so I'd like to save everyone else the pain.

+{% if argument.is_callback_interface %}
+{# FIXME: remove EventListener special case #}
+{% if argument.idl_type == 'EventListener' %}
+RefPtr<{{argument.idl_type}}> {{argument.name}};
+{% else %}
+OwnPtr<{{argument.idl_type}}> {{argument.name}};
+{% endif %}{# argument.idl_type == 'EventListener' #}
+{% elif argument.is_clamp %}{# argument.is_callback_interface #}
+{# NaN is treated as 0: http://www.w3.org/TR/WebIDL/#es-type-mapping #}
+{{argument.cpp_type}} {{argument.name}} = 0;
+{% elif argument.is_variadic_wrapper_type %}
+{{argument.vector_type}}<{{argument.cpp_type}} > {{argument.name}};
+{% else %}
+{{argument.cpp_type}} {{argument.name}};
+{% endif %}
+{% endmacro %}
+
+
+{######################################}
 {% macro generate_argument(method, argument, world_suffix) %}
 {% if argument.is_optional and not argument.has_default and
       argument.idl_type != 'Dictionary' and
       not argument.is_callback_interface %}
 {# Optional arguments without a default value generate an early call with
    fewer arguments if they are omitted.
    Optional Dictionary arguments default to empty dictionary. #}
 if (UNLIKELY(info.Length() <= {{argument.index}})) {
     {% if world_suffix %}
     {{cpp_method_call(method, argument.v8_set_return_value_for_main_world, argument.cpp_value) | indent}}
     {% else %}
     {{cpp_method_call(method, argument.v8_set_return_value, argument.cpp_value) | indent}}
     {% endif %}
     {% if argument.has_event_listener_argument %}
     {{hidden_dependency_action(method.name) | indent}}
     {% endif %}
     return;
 }
 {% endif %}
 {% if argument.has_type_checking_interface %}
 {# Type checking for wrapper interface types (if interface not implemented,
    throw a TypeError), per http://www.w3.org/TR/WebIDL/#es-interface #}
 if (info.Length() > {{argument.index}} && {% if argument.is_nullable %}!isUndefinedOrNull(info[{{argument.index}}]) && {% endif %}!V8{{argument.idl_type}}::hasInstance(info[{{argument.index}}], info.GetIsolate())) {
     {{throw_type_error(method, '"parameter %s is not of type \'%s\'."' %
                                (argument.index + 1, argument.idl_type)) | indent}}
     return;
 }
-{% endif %}
+{% endif %}{# argument.has_type_checking_interface #}
 {% if argument.is_callback_interface %}
 {# FIXME: remove EventListener special case #}
 {% if argument.idl_type == 'EventListener' %}
 {% if method.name == 'removeEventListener' %}
-RefPtr<{{argument.idl_type}}> {{argument.name}} = V8EventListenerList::getEventListener(info[1], false, ListenerFindOnly);
+{{argument.name}} = V8EventListenerList::getEventListener(info[1], false, ListenerFindOnly);
 {% else %}{# method.name == 'addEventListener' #}
-RefPtr<{{argument.idl_type}}> {{argument.name}} = V8EventListenerList::getEventListener(info[1], false, ListenerFindOrCreate);
+{{argument.name}} = V8EventListenerList::getEventListener(info[1], false, ListenerFindOrCreate);
 {% endif %}{# method.name #}
-{% else %}
+{% else %}{# argument.idl_type == 'EventListener' #}
 {# Callback functions must be functions:
    http://www.w3.org/TR/WebIDL/#es-callback-function #}
 {% if argument.is_optional %}
-OwnPtr<{{argument.idl_type}}> {{argument.name}};
 if (info.Length() > {{argument.index}} && !isUndefinedOrNull(info[{{argument.index}}])) {
     if (!info[{{argument.index}}]->IsFunction()) {
         {{throw_type_error(method,
               '"The callback provided as parameter %s is not a function."' %
                   (argument.index + 1)) | indent(8)}}
         return;
     }
     {{argument.name}} = V8{{argument.idl_type}}::create(v8::Handle<v8::Function>::Cast(info[{{argument.index}}]), currentExecutionContext(info.GetIsolate()));
 }
-{% else %}
+{% else %}{# argument.is_optional #}
 if (info.Length() <= {{argument.index}} || !{% if argument.is_nullable %}(info[{{argument.index}}]->IsFunction() || info[{{argument.index}}]->IsNull()){% else %}info[{{argument.index}}]->IsFunction(){% endif %}) {
     {{throw_type_error(method,
           '"The callback provided as parameter %s is not a function."' %
               (argument.index + 1)) | indent }}
     return;
 }
-OwnPtr<{{argument.idl_type}}> {{argument.name}} = {% if argument.is_nullable %}info[{{argument.index}}]->IsNull() ? nullptr : {% endif %}V8{{argument.idl_type}}::create(v8::Handle<v8::Function>::Cast(info[{{argument.index}}]), currentExecutionContext(info.GetIsolate()));
+{{argument.name}} = {% if argument.is_nullable %}info[{{argument.index}}]->IsNull() ? nullptr : {% endif %}V8{{argument.idl_type}}::create(v8::Handle<v8::Function>::Cast(info[{{argument.index}}]), currentExecutionContext(info.GetIsolate()));
 {% endif %}{# argument.is_optional #}
 {% endif %}{# argument.idl_type == 'EventListener' #}
 {% elif argument.is_clamp %}{# argument.is_callback_interface #}
 {# NaN is treated as 0: http://www.w3.org/TR/WebIDL/#es-type-mapping #}
-{{argument.cpp_type}} {{argument.name}} = 0;
-TONATIVE_VOID(double, {{argument.name}}NativeValue, info[{{argument.index}}]->NumberValue());
+double {{argument.name}}NativeValue;
+TONATIVE_VOID_NO_DECL({{argument.name}}NativeValue, info[{{argument.index}}]->NumberValue());
 if (!std::isnan({{argument.name}}NativeValue))
     {# IDL type is used for clamping, for the right bounds, since different
        IDL integer types have same internal C++ type (int or unsigned) #}
     {{argument.name}} = clampTo<{{argument.idl_type}}>({{argument.name}}NativeValue);
 {% elif argument.idl_type == 'SerializedScriptValue' %}
-{{argument.cpp_type}} {{argument.name}} = SerializedScriptValue::create(info[{{argument.index}}], 0, 0, exceptionState, info.GetIsolate());
+{{argument.name}} = SerializedScriptValue::create(info[{{argument.index}}], 0, 0, exceptionState, info.GetIsolate());
 if (exceptionState.throwIfNeeded())
     return;
 {% elif argument.is_variadic_wrapper_type %}
-{{argument.vector_type}}<{{argument.cpp_type}} > {{argument.name}};
 for (int i = {{argument.index}}; i < info.Length(); ++i) {
     if (!V8{{argument.idl_type}}::hasInstance(info[i], info.GetIsolate())) {
         {{throw_type_error(method, '"parameter %s is not of type \'%s\'."' %
                                    (argument.index + 1, argument.idl_type)) | indent(8)}}
         return;
     }
     {{argument.name}}.append(V8{{argument.idl_type}}::toNative(v8::Handle<v8::Object>::Cast(info[i])));
 }
 {% else %}
 {{argument.v8_value_to_local_cpp_value}};
@@ skipping 26 matching lines @@
 if (!{{argument.name}}.isUndefinedOrNull() && !{{argument.name}}.isObject()) {
     {{throw_type_error(method, '"parameter %s (\'%s\') is not an object."' %
                                (argument.index + 1, argument.name)) | indent}}
     return;
 }
 {% endif %}
 {% endmacro %}
 
 
 {######################################}
+{% macro generate_arguments(method, world_suffix) %}

[Nils Barth (inactive), 2014/05/07 03:02:19]

Could you move this *up* above the generate_argument_var and generate_argument
macros?
(Order here is top-down.)

+{% for argument in method.arguments %}
+{{generate_argument_var(argument) | indent}}

[Nils Barth (inactive), 2014/05/07 03:02:19]

No |indent|, trailing ; here.

+{% endfor %}
+{
+    {% if method.arguments_need_try_catch %}
+    v8::TryCatch block;
+    {% endif %}
+    {% for argument in method.arguments %}
+    {{generate_argument(method, argument, world_suffix) | indent}}
+    {% endfor %}
+}
+{% endmacro %}
+
+
+{######################################}
 {% macro cpp_method_call(method, v8_set_return_value, cpp_value) %}
 {# Local variables #}
 {% if method.is_partial_interface_member and not method.is_static %}
 {# instance members (non-static members) in partial interface take |impl| #}
 ASSERT(impl);
 {% endif %}
 {% if method.is_call_with_script_state %}
 ScriptState* state = ScriptState::current(info.GetIsolate());
 {% endif %}
 {% if method.is_call_with_execution_context %}
@@ skipping 194 matching lines @@
     {% if constructor.has_exception_state %}
     ExceptionState exceptionState(ExceptionState::ConstructionContext, "{{interface_name}}", info.Holder(), isolate);
     {% endif %}
     {% if interface_length and not constructor.overload_index %}
     {# FIXME: remove UNLIKELY: constructors are expensive, so no difference. #}
     if (UNLIKELY(info.Length() < {{interface_length}})) {
         {{throw_arity_type_error(constructor, interface_length)}};
         return;
     }
     {% endif %}
-    {% for argument in constructor.arguments %}
-    {{generate_argument(constructor, argument) | indent}}
-    {% endfor %}
+    {% if constructor.arguments %}

[Nils Barth (inactive), 2014/05/07 03:02:19]

Could you move this {% if %} test into the generate_arguments macro?
(Removes lots of duplication and simplifies call.)

[Jens Widell, 2014/05/07 10:34:46]

Would love to. One problem: I can't seem to figure out how to make it not
produce an empty line containing only four spaces for methods with no arguments.
Help? :-)

[Nils Barth (inactive), 2014/05/08 00:55:13]

Oh, good point (>.<)
That's exactly the trickiest point when using macros.
Could you try trimming trailing whitespace with -}} ?
(There are other hacky solutions, like putting the line break *before* the }} or
stripping leading whitespace before.)

If you can't get it working with a bit of fiddling, it's no problem;
this is exactly where it stops being worth worrying.

+    {{generate_arguments(constructor) | indent}}
+    {% endif %}
     {% if is_constructor_call_with_execution_context %}
     ExecutionContext* context = currentExecutionContext(isolate);
     {% endif %}
     {% if is_constructor_call_with_document %}
     Document& document = *toDocument(currentExecutionContext(isolate));
     {% endif %}
     {{constructor.cpp_type}} impl = {{cpp_class}}::create({{constructor.argument_list | join(', ')}});
     {% if is_constructor_raises_exception %}
     if (exceptionState.throwIfNeeded())
         return;
@@ skipping 43 matching lines @@
 
     {% if constructor.has_exception_state %}
     ExceptionState exceptionState(ExceptionState::ConstructionContext, "{{interface_name}}", info.Holder(), isolate);
     {% endif %}
     {% if constructor.number_of_required_arguments %}
     if (UNLIKELY(info.Length() < {{constructor.number_of_required_arguments}})) {
         {{throw_arity_type_error(constructor, constructor.number_of_required_arguments)}};
         return;
     }
     {% endif %}
-    {% for argument in constructor.arguments %}
-    {{generate_argument(constructor, argument) | indent}}
-    {% endfor %}
+    {% if constructor.arguments %}
+    {{generate_arguments(constructor) | indent}}
+    {% endif %}
     {{constructor.cpp_type}} impl = {{cpp_class}}::createForJSConstructor({{constructor.argument_list | join(', ')}});
     {% if is_constructor_raises_exception %}
     if (exceptionState.throwIfNeeded())
         return;
     {% endif %}
 
     {{generate_constructor_wrapper(constructor) | indent}}
 }
 {% endmacro %}