[WebAgentsAPI]: Introduce OverloadSetAdapter.

third_party/WebKit/Source/bindings/scripts/overload_set_algorithm.py

 # Copyright 2017 The Chromium Authors. All rights reserved.
 # coding=utf-8
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from collections import Counter
 import itertools
 from operator import itemgetter
 
 
 def sort_and_groupby(list_to_sort, key=None):
     """Returns a generator of (key, list), sorting and grouping list by key."""
     list_to_sort.sort(key=key)
     return ((k, list(g)) for k, g in itertools.groupby(list_to_sort, key))
 
 
-def effective_overload_set(F):  # pylint: disable=invalid-name
+class OverloadSetAdapter(object):
+    """Base class for the second effective_overload_set argument. Python is
+       a type-lax language, so this is mostly documentation of the expected
+       interface."""
+
+    def arguments(self, operation):
+        """Given an operation, return the list of its arguments."""
+        raise NotImplementedError
+
+    def type(self, argument):
+        """Given an argument, return its type."""
+        raise NotImplementedError
+
+    def is_optional(self, argument):
+        """Given an argument, return whether it is optional."""
+        raise NotImplementedError
+
+    def is_variadic(self, argument):
+        """"Given an argument, return whether it is variadic."""
+        raise NotImplementedError
+
+
+class MethodContextAdapter(OverloadSetAdapter):
+    def arguments(self, operation):
+        return operation['arguments']
+
+    def type(self, argument):
+        return argument['idl_type_object']
+
+    def is_optional(self, argument):
+        return argument['is_optional']
+
+    def is_variadic(self, argument):
+        return argument['is_variadic']
+
+
+def effective_overload_set(F, adapter):  # pylint: disable=invalid-name
     """Returns the effective overload set of an overloaded function.
 
     An effective overload set is the set of overloaded functions + signatures
     (type list of arguments, with optional and variadic arguments included or
     not), and is used in the overload resolution algorithm.
 
     For example, given input [f1(optional long x), f2(DOMString s)], the output
     is informally [f1(), f1(long), f2(DOMString)], and formally
     [(f1, [], []), (f1, [long], [optional]), (f2, [DOMString], [required])].
 
@@ skipping 10 matching lines @@
     variadics, but we don't use that currently.
 
     Spec: http://heycam.github.io/webidl/#dfn-effective-overload-set
 
     Formally the input and output lists are sets, but methods are stored
     internally as dicts, which can't be stored in a set because they are not
     hashable, so we use lists instead.
 
     Arguments:
         F: list of overloads for a given callable name.
+        value_reader: an OverloadSetValueReader instance.
 
     Returns:
         S: list of tuples of the form (callable, type list, optionality list).
     """
     # Code closely follows the algorithm in the spec, for clarity and
     # correctness, and hence is not very Pythonic.
 
     # 1. Initialize S to ∅.
     # (We use a list because we can't use a set, as noted above.)
     S = []  # pylint: disable=invalid-name
 
     # 2. Let F be a set with elements as follows, according to the kind of
     # effective overload set:
     # (Passed as argument, nothing to do.)
 
     # 3. & 4. (maxarg, m) are only needed for variadics, not used.
 
     # 5. For each operation, extended attribute or callback function X in F:
     for X in F:  # X is the "callable". pylint: disable=invalid-name
-        arguments = X['arguments']  # pylint: disable=invalid-name
+        arguments = adapter.arguments(X)  # pylint: disable=invalid-name
         # 1. Let n be the number of arguments X is declared to take.
         n = len(arguments)  # pylint: disable=invalid-name
         # 2. Let t0..n−1 be a list of types, where ti is the type of X’s
         # argument at index i.
         # (“type list”)
-        t = tuple(argument['idl_type_object']  # pylint: disable=invalid-name
+        t = tuple(adapter.type(argument)  # pylint: disable=invalid-name
                   for argument in arguments)
         # 3. Let o0..n−1 be a list of optionality values, where oi is “variadic”
         # if X’s argument at index i is a final, variadic argument, “optional”
         # if the argument is optional, and “required” otherwise.
         # (“optionality list”)
         # (We’re just using a boolean for optional/variadic vs. required.)
-        o = tuple(argument['is_optional']  # pylint: disable=invalid-name
-                  or argument['is_variadic'] for argument in arguments)
+        o = tuple(adapter.is_optional(argument)  # pylint: disable=invalid-name
+                  or adapter.is_variadic(argument)
+                  for argument in arguments)
         # 4. Add to S the tuple <X, t0..n−1, o0..n−1>.
         S.append((X, t, o))
         # 5. If X is declared to be variadic, then:
         # (Not used, so not implemented.)
         # 6. Initialize i to n−1.
         i = n - 1
         # 7. While i ≥ 0:
         # Spec bug (fencepost error); should be “While i > 0:”
         # https://www.w3.org/Bugs/Public/show_bug.cgi?id=25590
         while i > 0:
             # 1. If argument i of X is not optional, then break this loop.
             if not o[i]:
                 break
             # 2. Otherwise, add to S the tuple <X, t0..i−1, o0..i−1>.
             S.append((X, t[:i], o[:i]))
             # 3. Set i to i−1.
             i = i - 1
         # 8. If n > 0 and all arguments of X are optional, then add to S the
         # tuple <X, (), ()> (where “()” represents the empty list).
         if n > 0 and all(oi for oi in o):
-            S.append((X, [], []))
+            S.append((X, (), ()))
     # 6. The effective overload set is S.
     return S
 
 
 def effective_overload_set_by_length(overloads):
     def type_list_length(entry):
         # Entries in the effective overload set are 3-tuples:
         # (callable, type list, optionality list)
         return len(entry[1])
 
-    effective_overloads = effective_overload_set(overloads)
+    effective_overloads = effective_overload_set(overloads,
+                                                 MethodContextAdapter())
     return list(sort_and_groupby(effective_overloads, type_list_length))
 
 
 def method_overloads_by_name(methods):
     """Returns generator of overloaded methods by name: [name, [method]]"""
     # Filter to only methods that are actually overloaded
     method_counts = Counter(method['name'] for method in methods)
     overloaded_method_names = set(name
                                   for name, count in method_counts.iteritems()
                                   if count > 1)
     overloaded_methods = [method for method in methods
                           if method['name'] in overloaded_method_names]
 
     # Group by name (generally will be defined together, but not necessarily)
     return sort_and_groupby(overloaded_methods, itemgetter('name'))