Introduce CSSNodeCopyStyle

Summary:
- Add a convenience function to copy all style from one node to another.
- CSSNodeIsDirty will return true after this function if any style was changed in the destination node.

Reviewed By: emilsjolander

Differential Revision: D4188514

fbshipit-source-id: af8d7fb5e8688c64aea05ce7ad23fff9233fb441

tests/CSSLayoutStyleTest.cpp

@@ -0,0 +1,60 @@
+/**
+ * Copyright (c) 2014-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#include <CSSLayout/CSSLayout.h>
+#include <gtest/gtest.h>
+
+TEST(CSSLayoutTest, copy_style_same) {
+  const CSSNodeRef node0 = CSSNodeNew();
+  const CSSNodeRef node1 = CSSNodeNew();
+  ASSERT_FALSE(CSSNodeIsDirty(node0));
+
+  CSSNodeCopyStyle(node0, node1);
+  ASSERT_FALSE(CSSNodeIsDirty(node0));
+
+  CSSNodeFree(node0);
+  CSSNodeFree(node1);
+}
+
+TEST(CSSLayoutTest, copy_style_modified) {
+  const CSSNodeRef node0 = CSSNodeNew();
+  ASSERT_FALSE(CSSNodeIsDirty(node0));
+  ASSERT_EQ(CSSFlexDirectionColumn, CSSNodeStyleGetFlexDirection(node0));
+  ASSERT_TRUE(CSSValueIsUndefined(CSSNodeStyleGetMaxHeight(node0)));
+
+  const CSSNodeRef node1 = CSSNodeNew();
+  CSSNodeStyleSetFlexDirection(node1, CSSFlexDirectionRow);
+  CSSNodeStyleSetMaxHeight(node1, 10);
+
+  CSSNodeCopyStyle(node0, node1);
+  ASSERT_TRUE(CSSNodeIsDirty(node0));
+  ASSERT_EQ(CSSFlexDirectionRow, CSSNodeStyleGetFlexDirection(node0));
+  ASSERT_EQ(10, CSSNodeStyleGetMaxHeight(node0));
+
+  CSSNodeFree(node0);
+  CSSNodeFree(node1);
+}
+
+TEST(CSSLayoutTest, copy_style_modified_same) {
+  const CSSNodeRef node0 = CSSNodeNew();
+  CSSNodeStyleSetFlexDirection(node0, CSSFlexDirectionRow);
+  CSSNodeStyleSetMaxHeight(node0, 10);
+  CSSNodeCalculateLayout(node0, CSSUndefined, CSSUndefined, CSSDirectionLTR);
+  ASSERT_FALSE(CSSNodeIsDirty(node0));
+
+  const CSSNodeRef node1 = CSSNodeNew();
+  CSSNodeStyleSetFlexDirection(node1, CSSFlexDirectionRow);
+  CSSNodeStyleSetMaxHeight(node1, 10);
+
+  CSSNodeCopyStyle(node0, node1);
+  ASSERT_FALSE(CSSNodeIsDirty(node0));
+
+  CSSNodeFree(node0);
+  CSSNodeFree(node1);
+}