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 38c6d0b336eba5f24bb3cd89812be0faea8c87df..bad92c327d6713add4691ec588bde43ce5739e6b 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
@@ -12,9 +12,10 @@ 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
 
 
 # Temporary hard-coded list of fields that are not CSS properties.
@@ -69,6 +70,36 @@ NONPROPERTIES = [
 ]
 
 
+def _flatten_list(x):
+    """Flattens a list of lists into a single list."""
+    return list(chain.from_iterable(x))
+
+
+def _num_bit_field_buckets(bit_fields):

[meade_UTC10, 2017/04/06 03:29:57]

would this be better as something like

_num_32_bit_words_for_bit_fields

?

[shend, 2017/04/06 04:39:39]

Done.

+    """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):
+    def __init__(self, name, subgroups, fields):
+        """Represents a group of fields, which may contain subgroups that are dynamically allocated."""

[meade_UTC10, 2017/04/06 03:29:57]

Could you please document the types of the parameters? This will get more and
more important as the Python code gets bigger. 

Perhaps a followup CL could improve the documentation in this file (including
the parameter types, and things like below in field.__init__ the doc is "creates
a new field", which is completely useless).

[shend, 2017/04/06 04:39:39]

Agreed, the documentation in this file could be significantly improved.

+        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_bit_field_buckets = _num_bit_field_buckets(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.
@@ -99,12 +130,13 @@ class Field(object):
     """
 
     def __init__(self, field_role, name_for_methods, property_name, type_name,
-                 field_template, size, default_value, **kwargs):
+                 field_template, field_group, size, default_value, **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.field_group = field_group
         self.size = size
         self.default_value = default_value
 
@@ -146,6 +178,17 @@ def _get_include_paths(properties):
     return list(sorted(include_paths))
 
 
+def _group_fields(fields):
+    """Groups a list of fields by their field_group and returns the root group."""
+    groups = defaultdict(list)
+    for field in fields:
+        groups[field.field_group].append(field)
+
+    no_group = groups.pop(None)
+    subgroups = [Group(field_group, [], _reorder_fields(fields)) for field_group, 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]
@@ -209,6 +252,7 @@ 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,
     )
@@ -225,6 +269,7 @@ def _create_inherited_flag_field(property_):
         property_name=property_['name'],
         type_name='bool',
         field_template='flag',
+        field_group=property_['field_group'],
         size=1,
         default_value='true',
     )
@@ -248,11 +293,14 @@ def _create_fields(field_role, properties):
     return fields
 
 
-def _pack_fields(fields):
+def _reorder_fields(fields):

[meade_UTC10, 2017/04/06 03:29:57]

You're still doing packing though? I don't think this is a helpful renaming...

maybe something like _reorder_and_pack_members?

[shend, 2017/04/06 04:39:39]

For me, packing means the compiler "packing" the struct. What we're doing is
"reordering" so that the compiler can "pack" the struct.

     """
-    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]
+
     # 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
@@ -265,7 +313,7 @@ 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
@@ -278,7 +326,8 @@ 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):
@@ -299,6 +348,8 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
                 property_['field_type_path'] = None
             if 'type_name' not in property_:
                 property_['type_name'] = 'E' + enum_type_name(property_['name_for_methods'])
+            if 'field_group' not in property_:
+                property_['field_group'] = None
 
         property_values = self._properties.values()
 
@@ -309,46 +360,14 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
 
         self._generated_enums = _create_enums(property_values + NONPROPERTIES)
 
-        all_fields = (_create_fields('property', property_values) +
-                      _create_fields('nonproperty', NONPROPERTIES))
-
-        # 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)
+        fields = (_create_fields('property', property_values) +
+                  _create_fields('nonproperty', NONPROPERTIES))
 
-        self._include_paths = _get_include_paths(property_values + NONPROPERTIES)
+        # Separate fields into groups
+        self._base_group = _group_fields(fields)
 
+        # Get include paths

[meade_UTC10, 2017/04/06 03:29:57]

Is this really a helpful comment? :p

[shend, 2017/04/06 04:39:40]

lol, removed.

+        self._include_paths = _get_include_paths(property_values)
 
     @template_expander.use_jinja('ComputedStyleBase.h.tmpl')
     def generate_base_computed_style_h(self):
@@ -356,7 +375,7 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
             'properties': self._properties,
             'enums': self._generated_enums,
             'include_paths': self._include_paths,
-            'fields': self._fields,
+            'computed_style': self._base_group,
         }
 
     @template_expander.use_jinja('ComputedStyleBase.cpp.tmpl')
@@ -364,8 +383,7 @@ 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._base_group,
         }
 
     @template_expander.use_jinja('ComputedStyleBaseConstants.h.tmpl')
@@ -373,7 +391,6 @@ class ComputedStyleBaseWriter(make_style_builder.StyleBuilderWriter):
         return {
             'properties': self._properties,
             'enums': self._generated_enums,
-            'fields': self._fields,
         }
 
     @template_expander.use_jinja('CSSValueIDMappingsGenerated.h.tmpl')