1 files changed, 82 insertions, 0 deletions
diff --git a/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features.py b/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features.py
new file mode 100644
index 00000000..3cb73c5d
--- /dev/null
+++ b/utils/ipc/mojo/public/tools/mojom/mojom/parse/conditional_features.py
@@ -0,0 +1,82 @@
+# Copyright 2018 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+"""Helpers for processing conditionally enabled features in a mojom."""
+
+from mojom.error import Error
+from mojom.parse import ast
+
+
+class EnableIfError(Error):
+  """ Class for errors from ."""
+
+  def __init__(self, filename, message, lineno=None):
+    Error.__init__(self, filename, message, lineno=lineno, addenda=None)
+
+
+def _IsEnabled(definition, enabled_features):
+  """Returns true if a definition is enabled.
+
+  A definition is enabled if it has no EnableIf attribute, or if the value of
+  the EnableIf attribute is in enabled_features.
+  """
+  if not hasattr(definition, "attribute_list"):
+    return True
+  if not definition.attribute_list:
+    return True
+
+  already_defined = False
+  for a in definition.attribute_list:
+    if a.key == 'EnableIf':
+      if already_defined:
+        raise EnableIfError(
+            definition.filename,
+            "EnableIf attribute may only be defined once per field.",
+            definition.lineno)
+      already_defined = True
+
+  for attribute in definition.attribute_list:
+    if attribute.key == 'EnableIf' and attribute.value not in enabled_features:
+      return False
+  return True
+
+
+def _FilterDisabledFromNodeList(node_list, enabled_features):
+  if not node_list:
+    return
+  assert isinstance(node_list, ast.NodeListBase)
+  node_list.items = [
+      item for item in node_list.items if _IsEnabled(item, enabled_features)
+  ]
+  for item in node_list.items:
+    _FilterDefinition(item, enabled_features)
+
+
+def _FilterDefinition(definition, enabled_features):
+  """Filters definitions with a body."""
+  if isinstance(definition, ast.Enum):
+    _FilterDisabledFromNodeList(definition.enum_value_list, enabled_features)
+  elif isinstance(definition, ast.Interface):
+    _FilterDisabledFromNodeList(definition.body, enabled_features)
+  elif isinstance(definition, ast.Method):
+    _FilterDisabledFromNodeList(definition.parameter_list, enabled_features)
+    _FilterDisabledFromNodeList(definition.response_parameter_list,
+                                enabled_features)
+  elif isinstance(definition, ast.Struct):
+    _FilterDisabledFromNodeList(definition.body, enabled_features)
+  elif isinstance(definition, ast.Union):
+    _FilterDisabledFromNodeList(definition.body, enabled_features)
+
+
+def RemoveDisabledDefinitions(mojom, enabled_features):
+  """Removes conditionally disabled definitions from a Mojom node."""
+  mojom.import_list = ast.ImportList([
+      imported_file for imported_file in mojom.import_list
+      if _IsEnabled(imported_file, enabled_features)
+  ])
+  mojom.definition_list = [
+      definition for definition in mojom.definition_list
+      if _IsEnabled(definition, enabled_features)
+  ]
+  for definition in mojom.definition_list:
+    _FilterDefinition(definition, enabled_features)