Mojom backend: Stop re-computing version info and field packing data.

mojo/public/tools/bindings/pylib/mojom/generate/pack.py

Index: mojo/public/tools/bindings/pylib/mojom/generate/pack.py
diff --git a/mojo/public/tools/bindings/pylib/mojom/generate/pack.py b/mojo/public/tools/bindings/pylib/mojom/generate/pack.py
index b034f97a086a146f138c81c53e746b2e1487ee93..c898be0dd1f7ff6577fa0888cc814ec67de471a8 100644
--- a/mojo/public/tools/bindings/pylib/mojom/generate/pack.py
+++ b/mojo/public/tools/bindings/pylib/mojom/generate/pack.py
@@ -57,29 +57,18 @@ class PackedField(object):
       raise Exception("Invalid kind: %s" % kind.spec)
     return cls.kind_to_size[kind]
 
-  @classmethod
-  def GetAlignmentForKind(cls, kind):
-    if isinstance(kind, mojom.Interface):
-      return 4
-    if isinstance(kind, mojom.Union):
-      return 8
-    return cls.GetSizeForKind(kind)
-
-  def __init__(self, field, index, ordinal):
+  def __init__(self, field):
     """
     Args:
       field: the original field.
-      index: the position of the original field in the struct.
-      ordinal: the ordinal of the field for serialization.
     """
     self.field = field
-    self.index = index
-    self.ordinal = ordinal
+    self.index = field.declaration_order
+    self.ordinal = field.computed_ordinal
     self.size = self.GetSizeForKind(field.kind)
-    self.alignment = self.GetAlignmentForKind(field.kind)
-    self.offset = None
-    self.bit = None
-    self.min_version = None
+    self.offset = field.computed_offset
+    self.bit = field.computed_bit
+    self.min_version = field.computed_min_version
 
 
 def GetPad(offset, alignment):
@@ -88,94 +77,20 @@ def GetPad(offset, alignment):
   return (alignment - (offset % alignment)) % alignment
 
 
-def GetFieldOffset(field, last_field):
-  """Returns a 2-tuple of the field offset and bit (for BOOLs)."""
-  if (field.field.kind == mojom.BOOL and
-      last_field.field.kind == mojom.BOOL and
-      last_field.bit < 7):
-    return (last_field.offset, last_field.bit + 1)
-
-  offset = last_field.offset + last_field.size
-  pad = GetPad(offset, field.alignment)
-  return (offset + pad, 0)
-
-
-def GetPayloadSizeUpToField(field):
-  """Returns the payload size (not including struct header) if |field| is the
-  last field.
-  """
-  if not field:
-    return 0
-  offset = field.offset + field.size
-  pad = GetPad(offset, 8)
-  return offset + pad
-
-
 class PackedStruct(object):
   def __init__(self, struct):
     self.struct = struct
-    # |packed_fields| contains all the fields, in increasing offset order.
-    self.packed_fields = []
-    # |packed_fields_in_ordinal_order| refers to the same fields as
-    # |packed_fields|, but in ordinal order.
-    self.packed_fields_in_ordinal_order = []
-
-    # No fields.
-    if (len(struct.fields) == 0):
-      return
-
-    # Start by sorting by ordinal.
-    src_fields = self.packed_fields_in_ordinal_order
-    ordinal = 0
-    for index, field in enumerate(struct.fields):
-      if field.ordinal is not None:
-        ordinal = field.ordinal
-      src_fields.append(PackedField(field, index, ordinal))
-      ordinal += 1
-    src_fields.sort(key=lambda field: field.ordinal)
-
-    # Set |min_version| for each field.
-    next_min_version = 0
-    for packed_field in src_fields:
-      if packed_field.field.min_version is None:
-        assert next_min_version == 0
-      else:
-        assert packed_field.field.min_version >= next_min_version
-        next_min_version = packed_field.field.min_version
-      packed_field.min_version = next_min_version
-
-      if (packed_field.min_version != 0 and
-          mojom.IsReferenceKind(packed_field.field.kind) and
-          not packed_field.field.kind.is_nullable):
-        raise Exception("Non-nullable fields are only allowed in version 0 of "
-                        "a struct. %s.%s is defined with [MinVersion=%d]."
-                            % (self.struct.name, packed_field.field.name,
-                               packed_field.min_version))
-
-    src_field = src_fields[0]
-    src_field.offset = 0
-    src_field.bit = 0
-    dst_fields = self.packed_fields
-    dst_fields.append(src_field)
-
-    # Then find first slot that each field will fit.
-    for src_field in src_fields[1:]:
-      last_field = dst_fields[0]
-      for i in xrange(1, len(dst_fields)):
-        next_field = dst_fields[i]
-        offset, bit = GetFieldOffset(src_field, last_field)
-        if offset + src_field.size <= next_field.offset:
-          # Found hole.
-          src_field.offset = offset
-          src_field.bit = bit
-          dst_fields.insert(i, src_field)
-          break
-        last_field = next_field
-      if src_field.offset is None:
-        # Add to end
-        src_field.offset, src_field.bit = GetFieldOffset(src_field, last_field)
-        dst_fields.append(src_field)
 
+    # |packed_fields_in_ordinal_order| contains all the fields,
+    # in ordinal order.
+    self.packed_fields_in_ordinal_order = [PackedField(field)
+        for field in struct.fields_in_ordinal_order]
+
+    # |packed_fields| refers to the same fields as
+    # |packed_fields_in_ordinal_order|, but in increasing offset order.
+    self.packed_fields = [field for field in
+        self.packed_fields_in_ordinal_order]
+    self.packed_fields.sort(key=lambda f: (f.offset, f.bit))
 
 class ByteInfo(object):
   def __init__(self):
@@ -184,8 +99,7 @@ class ByteInfo(object):
 
 
 def GetByteLayout(packed_struct):
-  total_payload_size = GetPayloadSizeUpToField(
-      packed_struct.packed_fields[-1] if packed_struct.packed_fields else None)
+  total_payload_size = packed_struct.struct.versions[-1].num_bytes - HEADER_SIZE
   bytes = [ByteInfo() for i in xrange(total_payload_size)]
 
   limit_of_previous_field = 0
@@ -211,38 +125,3 @@ class VersionInfo(object):
     self.num_fields = num_fields
     self.num_bytes = num_bytes
 
-
-def GetVersionInfo(packed_struct):
-  """Get version information for a struct.
-
-  Args:
-    packed_struct: A PackedStruct instance.
-
-  Returns:
-    A non-empty list of VersionInfo instances, sorted by version in increasing
-    order.
-    Note: The version numbers may not be consecutive.
-  """
-  versions = []
-  last_version = 0
-  last_num_fields = 0
-  last_payload_size = 0
-
-  for packed_field in packed_struct.packed_fields_in_ordinal_order:
-    if packed_field.min_version != last_version:
-      versions.append(
-          VersionInfo(last_version, last_num_fields,
-                      last_payload_size + HEADER_SIZE))
-      last_version = packed_field.min_version
-
-    last_num_fields += 1
-    # The fields are iterated in ordinal order here. However, the size of a
-    # version is determined by the last field of that version in pack order,
-    # instead of ordinal order. Therefore, we need to calculate the max value.
-    last_payload_size = max(GetPayloadSizeUpToField(packed_field),
-                            last_payload_size)
-
-  assert len(versions) == 0 or last_num_fields != versions[-1].num_fields
-  versions.append(VersionInfo(last_version, last_num_fields,
-                              last_payload_size + HEADER_SIZE))
-  return versions