IDL: Support runtime enabled overloads affecting Function.length

Source/bindings/scripts/v8_interface.py

 # Copyright (C) 2013 Google Inc. All rights reserved.
 # coding=utf-8
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 351 matching lines @@
         if 'overloads' in method:
             overloads = method['overloads']
             if not overloads['visible']:
                 continue
             # original interface will register instead of partial interface.
             if overloads['has_partial_overloads'] and interface.is_partial:
                 continue
             per_context_enabled_function = overloads['per_context_enabled_function_all']
             conditionally_exposed_function = overloads['exposed_test_all']
             runtime_enabled_function = overloads['runtime_enabled_function_all']
-            has_custom_registration = overloads['has_custom_registration_all']
+            has_custom_registration = (overloads['has_custom_registration_all'] or
+                                       overloads['runtime_determined_lengths'])
         else:
             if not method['visible']:
                 continue
             per_context_enabled_function = method['per_context_enabled_function']
             conditionally_exposed_function = method['exposed_test']
             runtime_enabled_function = method['runtime_enabled_function']
             has_custom_registration = method['has_custom_registration']
 
         if per_context_enabled_function or conditionally_exposed_function:
             conditionally_enabled_methods.append(method)
@@ skipping 112 matching lines @@
     and returns dict of overall overload template values.
     """
     assert len(overloads) > 1  # only apply to overloaded names
     for index, method in enumerate(overloads, 1):
         method['overload_index'] = index
 
     effective_overloads_by_length = effective_overload_set_by_length(overloads)
     lengths = [length for length, _ in effective_overloads_by_length]
     name = overloads[0].get('name', '<constructor>')
 
-    # Check and fail if all overloads with the shortest acceptable arguments
-    # list are runtime enabled, since we would otherwise set 'length' on the
-    # function object to an incorrect value when none of those overloads were
-    # actually enabled at runtime. The exception is if all overloads are
-    # controlled by the same runtime enabled feature, in which case there would
-    # be no function object at all if it is not enabled.
+    # Check if all overloads with the shortest acceptable arguments list are
+    # runtime enabled, in which case we need to have a runtime determined
+    # Function.length. The exception is if all overloads are controlled by the
+    # same runtime enabled feature, in which case there would be no function
+    # object at all if it is not enabled.
     shortest_overloads = effective_overloads_by_length[0][1]
     if (all(method.get('runtime_enabled_function')
             for method, _, _ in shortest_overloads) and
         not common_value(overloads, 'runtime_enabled_function')):
-        raise ValueError('Function.length of %s depends on runtime enabled features' % name)
+        # Generate a list of (length, runtime_enabled_functions) tuples.
+        runtime_determined_lengths = []
+        for length, effective_overloads in effective_overloads_by_length:
+            runtime_enabled_functions = set(
+                method['runtime_enabled_function']
+                for method, _, _ in effective_overloads
+                if method.get('runtime_enabled_function'))
+            if not runtime_enabled_functions:
+                # This "length" is unconditionally enabled, so stop here.
+                runtime_determined_lengths.append((length, [None]))
+                break
+            runtime_determined_lengths.append(
+                (length, sorted(runtime_enabled_functions)))
+        length = ('%sV8Internal::%sMethodLength()'
+                  % (cpp_name_or_partial(interface), name))
+    else:
+        runtime_determined_lengths = None
+        length = lengths[0]
 
     # Check and fail if overloads disagree on any of the extended attributes
     # that affect how the method should be registered.
     # Skip the check for overloaded constructors, since they don't support any
     # of the extended attributes in question.
     if not overloads[0].get('is_constructor'):
         overload_extended_attributes = [
             method['custom_registration_extended_attributes']
             for method in overloads]
         for extended_attribute in v8_methods.CUSTOM_REGISTRATION_EXTENDED_ATTRIBUTES:
@@ skipping 19 matching lines @@
             has_overload_not_visible = True
 
     # If some overloads are not visible and others are visible,
     # the method is overloaded between core and modules.
     has_partial_overloads = has_overload_visible and has_overload_not_visible
 
     return {
         'deprecate_all_as': common_value(overloads, 'deprecate_as'),  # [DeprecateAs]
         'exposed_test_all': common_value(overloads, 'exposed_test'),  # [Exposed]
         'has_custom_registration_all': common_value(overloads, 'has_custom_registration'),
+        'length': length,
         'length_tests_methods': length_tests_methods(effective_overloads_by_length),
         # 1. Let maxarg be the length of the longest type list of the
         # entries in S.
         'maxarg': lengths[-1],
         'measure_all_as': common_value(overloads, 'measure_as'),  # [MeasureAs]
         'minarg': lengths[0],
         'per_context_enabled_function_all': common_value(overloads, 'per_context_enabled_function'),  # [PerContextEnabled]
         'returns_promise_all': promise_overload_count > 0,
+        'runtime_determined_lengths': runtime_determined_lengths,
         'runtime_enabled_function_all': common_value(overloads, 'runtime_enabled_function'),  # [RuntimeEnabled]
         'valid_arities': lengths
             # Only need to report valid arities if there is a gap in the
             # sequence of possible lengths, otherwise invalid length means
             # "not enough arguments".
             if lengths[-1] - lengths[0] != len(lengths) - 1 else None,
         'visible': has_overload_visible,
         'has_partial_overloads': has_partial_overloads,
     }
 
@@ skipping 663 matching lines @@
         deleter = next(
             method
             for method in interface.operations
             if ('deleter' in method.specials and
                 len(method.arguments) == 1 and
                 str(method.arguments[0].idl_type) == 'DOMString'))
     except StopIteration:
         return None
 
     return property_deleter(deleter)