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

CSSLayout/CSSLayout.c

@@ -341,6 +341,13 @@ bool CSSNodeIsDirty(const CSSNodeRef node) {
   return node->isDirty;
 }
 
+void CSSNodeCopyStyle(const CSSNodeRef dstNode, const CSSNodeRef srcNode) {
+  if (memcmp(&dstNode->style, &srcNode->style, sizeof(CSSStyle)) != 0) {
+    memcpy(&dstNode->style, &srcNode->style, sizeof(CSSStyle));
+    _CSSNodeMarkDirty(dstNode);
+  }
+}
+
 inline float CSSNodeStyleGetFlexGrow(CSSNodeRef node) {
   if (!CSSValueIsUndefined(node->style.flexGrow)) {
     return node->style.flexGrow;

CSSLayout/CSSLayout.h

@@ -98,6 +98,8 @@ WIN_EXPORT bool CSSNodeCanUseCachedMeasurement(const CSSMeasureMode widthMode,
                                                const float marginRow,
                                                const float marginColumn);
 
+WIN_EXPORT void CSSNodeCopyStyle(const CSSNodeRef dstNode, const CSSNodeRef srcNode);
+
 #define CSS_NODE_PROPERTY(type, name, paramName)                           \
   WIN_EXPORT void CSSNodeSet##name(const CSSNodeRef node, type paramName); \
   WIN_EXPORT type CSSNodeGet##name(const CSSNodeRef node);

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);
+}