binding: Indexed property returns undefined if out-of-range.

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

Index: third_party/WebKit/Source/bindings/templates/interface.cpp
diff --git a/third_party/WebKit/Source/bindings/templates/interface.cpp b/third_party/WebKit/Source/bindings/templates/interface.cpp
index 5dd75b43e0748b7a891b2a09fc1f3b0a30b9beee..9cf59f635e886cc5a3e79496b893ebce1814256b 100644
--- a/third_party/WebKit/Source/bindings/templates/interface.cpp
+++ b/third_party/WebKit/Source/bindings/templates/interface.cpp
@@ -21,6 +21,13 @@ static void indexedPropertyGetter(uint32_t index, const v8::PropertyCallbackInfo
 
     {{cpp_class}}* impl = {{v8_class}}::toImpl(info.Holder());
 
+    // We assume that all the implementations support length() method, although

[peria, 2016/09/14 15:25:03]

Please use "{#...#}" style comment not to generate code with comments.

[Yuki, 2016/09/15 09:49:17]

I intentionally made this comment C++ comment so that it's visible to Blink
developers.

If someone implements a new interface (or updates an existing interface) and
hits a compile error that class T does not declare length(), this comment will
be useful for Blink developers to understand why the compile error happens.

+    // the spec doesn't require that length() must exist.  It's okay that
+    // the interface does not have length attribute as long as the
+    // implementation supports length() member function.
+    if (index >= impl->length())
+        return;  // Returns undefined due to out-of-range.
+
     {% set getter_name = getter.name or 'anonymousIndexedGetter' %}
     {% set getter_arguments = ['index'] %}
     {% if getter.is_call_with_script_state %}
@@ -31,8 +38,6 @@ static void indexedPropertyGetter(uint32_t index, const v8::PropertyCallbackInfo
     {% set getter_arguments = getter_arguments + ['exceptionState'] %}
     {% endif %}
     {{getter.cpp_type}} result = impl->{{getter_name}}({{getter_arguments | join(', ')}});
-    if ({{getter.is_null_expression}})
-        return;
     {{getter.v8_set_return_value}};
 }