Generate subgroup StyleSurroundData in ComputedStyle.

third_party/WebKit/Source/build/scripts/make_computed_style_base.py

Index: third_party/WebKit/Source/build/scripts/make_computed_style_base.py
diff --git a/third_party/WebKit/Source/build/scripts/make_computed_style_base.py b/third_party/WebKit/Source/build/scripts/make_computed_style_base.py
index 8bce1cf151b3e2148836b41409a0f3e14e364160..aec595111d91a99eb44f61cd7935b39eca0758a7 100755
--- a/third_party/WebKit/Source/build/scripts/make_computed_style_base.py
+++ b/third_party/WebKit/Source/build/scripts/make_computed_style_base.py
@@ -12,10 +12,12 @@ import make_style_builder
 
 from name_utilities import (
     enum_for_css_keyword, enum_type_name, enum_value_name, class_member_name, method_name,
-    join_name
+    class_name, join_name
 )
-from collections import OrderedDict
+from collections import defaultdict, OrderedDict
+from itertools import chain
 
+# TODO(shend): Improve documentation and add docstrings.
 
 # Temporary hard-coded list of extra fields.
 # TODO(shend): Put this into its own JSON5 file.
@@ -74,9 +76,58 @@ EXTRA_FIELDS = [
     # once we can support union fields and groups.
     {'name': 'VerticalAlign', 'field_template': 'storage_only', 'field_size': 4, 'default_value': 'EVerticalAlign::kBaseline',
      'type_name': 'EVerticalAlign', 'inherited': False, 'independent': False},
+    # Fields that are shared by multiple properties.
+    # TODO(shend): Try to split these up to one field per property.
+    {'name': 'margin', 'field_template': 'storage_only', 'field_size': None, 'field_type_path': 'platform/LengthBox',
+     'type_name': 'LengthBox', 'field_group': 'surround', 'default_value': 'LengthBox(kFixed)', 'inherited': False,
+     'independent': False, 'has_custom_compare_and_copy': False},
+    {'name': 'padding', 'field_template': 'storage_only', 'field_size': None, 'field_type_path': 'platform/LengthBox',
+     'type_name': 'LengthBox', 'field_group': 'surround', 'default_value': 'LengthBox(kFixed)', 'inherited': False,
+     'independent': False, 'has_custom_compare_and_copy': False},
+    {'name': 'border', 'field_template': 'storage_only', 'field_size': None, 'field_type_path': 'core/style/BorderData',
+     'type_name': 'BorderData', 'field_group': 'surround', 'default_value': 'BorderData()', 'inherited': False,
+     'independent': False, 'has_custom_compare_and_copy': False},
 ]
 
 
+def _flatten_list(x):
+    """Flattens a list of lists into a single list."""
+    return list(chain.from_iterable(x))
+
+
+def _num_32_bit_words_for_bit_fields(bit_fields):
+    """Gets the number of 32 bit unsigned integers needed store a list of bit fields."""
+    num_buckets, cur_bucket = 0, 0
+    for field in bit_fields:
+        if field.size + cur_bucket > 32:
+            num_buckets += 1
+            cur_bucket = 0
+        cur_bucket += field.size
+    return num_buckets + (cur_bucket > 0)
+
+
+class Group(object):
+    """Represents a group of fields stored together in a class.
+
+    Attributes:
+        name: The name of the group as a string.
+        subgroups: List of Group instances that are stored as subgroups under this group.
+        fields: List of Field instances stored directly under this group.
+    """
+    def __init__(self, name, subgroups, fields):
+        self.name = name
+        self.subgroups = subgroups
+        self.fields = fields
+        self.type_name = class_name(join_name('style', name, ' data'))
+        self.member_name = class_member_name(name)
+        self.num_32_bit_words_for_bit_fields = _num_32_bit_words_for_bit_fields(
+            field for field in fields if field.is_bit_field
+        )
+
+        # Recursively get all the fields in the subgroups as well
+        self.all_fields = _flatten_list(subgroup.all_fields for subgroup in subgroups) + fields
+
+
 class Field(object):
     """
     The generated ComputedStyle object is made up of a series of Fields.
@@ -102,18 +153,20 @@ class Field(object):
         type_name: Name of the C++ type exposed by the generated interface (e.g. EClear, int).
         field_template: Determines the interface generated for the field. Can be one of:
            keyword, flag, or monotonic_flag.
+        group_member_name: The class member name representing the group.

[meade_UTC10, 2017/04/20 03:08:40]

This is the first time you mention groups in this class doc - is it the group
the field is inside, or is it a group contained within the field?

[shend, 2017/04/20 03:22:34]

Clarified the comment.

         size: Number of bits needed for storage.
         default_value: Default value for this field when it is first initialized.
     """
 
     def __init__(self, field_role, name_for_methods, property_name, type_name,
-                 field_template, size, default_value, getter_method_name, setter_method_name,
-                 initial_method_name, **kwargs):
+                 field_template, field_group, size, default_value,
+                 getter_method_name, setter_method_name, initial_method_name, **kwargs):
         """Creates a new field."""
         self.name = class_member_name(name_for_methods)
         self.property_name = property_name
         self.type_name = type_name
         self.field_template = field_template
+        self.group_member_name = class_member_name(field_group) if field_group else None
         self.size = size
         self.default_value = default_value
 
@@ -154,6 +207,17 @@ def _get_include_paths(properties):
     return list(sorted(include_paths))
 
 
+def _group_fields(fields):
+    """Groups a list of fields by their group_member_name and returns the root group."""
+    groups = defaultdict(list)
+    for field in fields:
+        groups[field.group_member_name].append(field)
+
+    no_group = groups.pop(None)
+    subgroups = [Group(group_member_name, [], _reorder_fields(fields)) for group_member_name, fields in groups.items()]
+    return Group('', subgroups=subgroups, fields=_reorder_fields(no_group))
+
+
 def _create_enums(properties):
     """
     Returns an OrderedDict of enums to be generated, enum name -> [list of enum values]
@@ -221,6 +285,7 @@ def _create_field(field_role, property_):
         independent=property_['independent'],
         type_name=type_name,
         field_template=property_['field_template'],
+        field_group=property_['field_group'],
         size=size,
         default_value=default_value,
         getter_method_name=property_['getter'],
@@ -241,6 +306,7 @@ def _create_inherited_flag_field(property_):
         property_name=property_['name'],
         type_name='bool',
         field_template='primitive',
+        field_group=property_['field_group'],
         size=1,
         default_value='true',
         getter_method_name=method_name(name_for_methods),
@@ -271,11 +337,14 @@ def _create_fields(properties):
     return fields
 
 
-def _pack_fields(fields):
+def _reorder_fields(fields):
     """
-    Group a list of fields into buckets to minimise padding.
-    Returns a list of buckets, where each bucket is a list of Field objects.
+    Returns a list of fields ordered to minimise padding.
     """
+    # Separate out bit fields from normal fields
+    bit_fields = [field for field in fields if field.is_bit_field]
+    normal_fields = [field for field in fields if not field.is_bit_field]

[meade_UTC10, 2017/04/20 03:08:40]

normal -> fields that are some type other than a bit field? bit_fields vs
non_bit_fields maybe?

[shend, 2017/04/20 03:22:34]

Changed to non_bit_fields.

+
     # Since fields cannot cross word boundaries, in order to minimize
     # padding, group fields into buckets so that as many buckets as possible
     # are exactly 32 bits. Although this greedy approach may not always
@@ -288,7 +357,7 @@ def _pack_fields(fields):
     field_buckets = []
     # Consider fields in descending order of size to reduce fragmentation
     # when they are selected. Ties broken in alphabetical order by name.
-    for field in sorted(fields, key=lambda f: (-f.size, f.name)):
+    for field in sorted(bit_fields, key=lambda f: (-f.size, f.name)):
         added_to_bucket = False
         # Go through each bucket and add this field if it will not increase
         # the bucket's size to larger than 32 bits. Otherwise, make a new
@@ -301,7 +370,8 @@ def _pack_fields(fields):
         if not added_to_bucket:
             field_buckets.append([field])
 
-    return field_buckets
+    # Normal fields go first, then the bit fields.
+    return list(normal_fields) + _flatten_list(field_buckets)
 
 
 class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
@@ -324,8 +394,6 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
 
         # TODO(shend): Remove this once we move EXTRA_FIELDS to its own JSON file,
         # since the JSON5 reader will handle missing fields and defaults.
-        # TODO(shend): Remove this once we move NONPROPERTIES to its own JSON file,
-        # since the JSON5 reader will handle missing fields and defaults.
         for property_ in EXTRA_FIELDS:
             for parameter in self.json5_file.parameters:
                 if parameter not in property_:
@@ -334,7 +402,8 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
         for property_ in EXTRA_FIELDS:
             # TODO(shend): Remove the line below once we move EXTRA_FIELDS to its
             # own file which would enforce defaults.
-            property_['has_custom_compare_and_copy'] = True
+            if 'has_custom_compare_and_copy' not in property_:
+                property_['has_custom_compare_and_copy'] = True
             make_style_builder.apply_property_naming_defaults(property_)
 
         all_properties = css_properties + EXTRA_FIELDS
@@ -348,40 +417,9 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
 
         all_fields = _create_fields(all_properties)
 
-        # Separate the normal fields from the bit fields
-        bit_fields = [field for field in all_fields if field.is_bit_field]
-        normal_fields = [field for field in all_fields if not field.is_bit_field]
-
-        # Pack bit fields into buckets
-        field_buckets = _pack_fields(bit_fields)
-
-        # The expected size of ComputedStyleBase is equivalent to as many words
-        # as the total number of buckets.
-        self._expected_bit_field_bytes = len(field_buckets)
-
-        # The most optimal size of ComputedStyleBase is the total sum of all the
-        # field sizes, rounded up to the nearest word. If this produces the
-        # incorrect value, either the packing algorithm is not optimal or there
-        # is no way to pack the fields such that excess padding space is not
-        # added.
-        # If this fails, increase extra_padding_bytes by 1, but be aware that
-        # this also increases ComputedStyleBase by 1 word.
-        # We should be able to bring extra_padding_bytes back to 0 from time to
-        # time.
-        extra_padding_bytes = 0
-        optimal_bit_field_bytes = int(math.ceil(sum(f.size for f in bit_fields) / 32.0))
-        real_bit_field_bytes = optimal_bit_field_bytes + extra_padding_bytes
-        assert self._expected_bit_field_bytes == real_bit_field_bytes, \
-            ('The field packing algorithm produced %s bytes, optimal is %s bytes' %
-             (self._expected_bit_field_bytes, real_bit_field_bytes))
-
-        # Normal fields go first, then the bit fields.
-        self._fields = list(normal_fields)
-
-        # Order the fields so fields in each bucket are adjacent.
-        for bucket in field_buckets:
-            for field in bucket:
-                self._fields.append(field)
+        # Organise fields into a tree structure where the root group
+        # is ComputedStyleBase.
+        self._root_group = _group_fields(all_fields)
 
         self._include_paths = _get_include_paths(all_properties)
         self._outputs = {
@@ -396,7 +434,7 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
             'properties': self._properties,
             'enums': self._generated_enums,
             'include_paths': self._include_paths,
-            'fields': self._fields,
+            'computed_style': self._root_group,
         }
 
     @template_expander.use_jinja('ComputedStyleBase.cpp.tmpl')
@@ -404,8 +442,7 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
         return {
             'properties': self._properties,
             'enums': self._generated_enums,
-            'fields': self._fields,
-            'expected_bit_field_bytes': self._expected_bit_field_bytes,
+            'computed_style': self._root_group,
         }
 
     @template_expander.use_jinja('ComputedStyleBaseConstants.h.tmpl')
@@ -413,7 +450,6 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
         return {
             'properties': self._properties,
             'enums': self._generated_enums,
-            'fields': self._fields,
         }
 
 if __name__ == '__main__':