IDL compiler: anonymous indexed property getters

Source/bindings/scripts/unstable/v8_interface.py

Index: Source/bindings/scripts/unstable/v8_interface.py
diff --git a/Source/bindings/scripts/unstable/v8_interface.py b/Source/bindings/scripts/unstable/v8_interface.py
index 78b1e7205e831a7ac9021d0fc343cfc62db88ff5..1f97a5cf9612fa74ce5fa13574c7239ecdb50812 100644
--- a/Source/bindings/scripts/unstable/v8_interface.py
+++ b/Source/bindings/scripts/unstable/v8_interface.py
@@ -201,7 +201,8 @@ def generate_interface(interface):
     })
 
     methods = [v8_methods.generate_method(interface, method)
-               for method in interface.operations]
+               for method in interface.operations
+               if method.name]  # Skip anonymous special operations (methods)
     generate_overloads(methods)
     for method in methods:
         method['do_generate_method_configuration'] = (
@@ -219,6 +220,10 @@ def generate_interface(interface):
         'methods': methods,
     })
 
+    template_contents.update({
+        'anonymous_indexed_property_getter': generate_anonymous_indexed_property_getter(interface),
+    })
+
     return template_contents
 
 
@@ -463,3 +468,36 @@ def interface_length(interface, constructors):
         return 0
     return min(constructor['number_of_required_arguments']
                for constructor in constructors)
+
+
+################################################################################
+# Special operations (methods)
+# http://heycam.github.io/webidl/#idl-special-operations
+################################################################################
+
+def generate_anonymous_indexed_property_getter(interface):
+    try:
+        getter = next(

[haraken, 2014/01/27 06:35:32]

This looks a bit complicated. Can we avoid using Python's generator?

[Nils Barth (inactive), 2014/01/27 06:59:35]

Admittedly this looks a bit weird, but this is the most idiomatic way in
Python to get the first matching element of a list, basically because
generator expressions/list comprehensions are the idiomatic way to
*filter* a list:
http://stackoverflow.com/questions/9542738/python-find-in-list

The actual syntax is pretty simple:
try:
    foo = next(x for x in l if f(x))
except StopIteration:
    return None

The alternative:
for x in l:
    if f(x):
        foo = x
        break
else:
    return None
...is rather longer, and buries the assignment (the point of the statement!)
2 levels deep.

I used this last week, but the condition was simple, so it didn't
look so bad.

The actual complexity here is the condition statement,
because the parser doesn't select the indexed getter for us,
so we have to search for it.

I could put this obnoxious complexity in the parser,
once Perl is gone.

In Perl the search has special function, GetSpecialAccessorFunctionForType,
which is even longer and more complicated;
I think it's clearer to explicitly inline the test.

[haraken, 2014/01/27 07:04:40]

Understood, thanks for the clarification.

+            method
+            for method in interface.operations
+            if ('getter' in method.specials and
+                len(method.arguments) == 1 and
+                method.arguments[0].idl_type == 'unsigned long' and
+                not method.name))
+    except StopIteration:
+        return None
+
+    idl_type = getter.idl_type
+    extended_attributes = getter.extended_attributes
+    return {
+        'cpp_type': v8_types.cpp_type(idl_type),
+        'is_null_expression': getter_is_null_expression(idl_type),
+        'name': extended_attributes['ImplementedAs'],

[haraken, 2014/01/27 06:35:32]

Why do we need to support [ImplementedAs] for "anonymous" indexed properties?

[Nils Barth (inactive), 2014/01/27 06:59:35]

See other comment:
anonymous means there's no name in the *IDL*,
but we need a name for the function in the Blink C++.

I'd prefer to remove this and default to a standard name,
like anonymousIndexedGetter (which is used in several IDLs).

[haraken, 2014/01/27 07:04:40]

Sounds better.

[Nils Barth (inactive), 2014/01/27 07:24:37]

Ok, I'll do this in a followup, as it touches real IDLs.

+        'v8_set_return_value': v8_types.v8_set_return_value(idl_type, 'element', extended_attributes=extended_attributes, script_wrappable='collection'),
+    }
+
+
+def getter_is_null_expression(idl_type):

[haraken, 2014/01/27 06:35:32]

Is this method only for getters?

[Nils Barth (inactive), 2014/01/27 06:59:35]

Yes; I've thus made it explicit.

+    if idl_type == 'DOMString':
+        return 'element.isNull()'
+    return None

[haraken, 2014/01/27 06:35:32]

How can we judge nullability for non-DOMString values?

[Nils Barth (inactive), 2014/01/27 06:59:35]

See GenerateIsNullExpression
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit...

For interface types it's just !element, while for union types we need to recurse
on the elements.

I'll do this in followups, per type.