Fabric: TextAttributes::defaultTextAttributes()

Summary: An `AttributedString` object generated by a cross-platform layer of React Native must have already resolved text styles to make the actual resulting text identical across platforms. To do so we have to have a unified default.

Reviewed By: sahrens

Differential Revision: D10287725

fbshipit-source-id: e8c62b33496be34146182baccd0009d3624a7fe5

ReactCommon/fabric/attributedstring/TextAttributes.cpp

@@ -149,6 +149,18 @@ bool TextAttributes::operator!=(const TextAttributes &rhs) const {
   return !(*this == rhs);
 }
 
+TextAttributes TextAttributes::defaultTextAttributes() {
+  static auto textAttributes = [] {
+    auto textAttributes = TextAttributes{};
+    // Non-obvious (can be different among platforms) default text attributes.
+    textAttributes.foregroundColor = blackColor();
+    textAttributes.backgroundColor = clearColor();
+    textAttributes.fontSize = 12.0;
+    return textAttributes;
+  }();
+  return textAttributes;
+}
+
 #pragma mark - DebugStringConvertible
 
 #if RN_DEBUG_STRING_CONVERTIBLE

ReactCommon/fabric/attributedstring/TextAttributes.h

@@ -27,6 +27,13 @@ using SharedTextAttributes = std::shared_ptr<const TextAttributes>;
 
 class TextAttributes : public DebugStringConvertible {
  public:
+  /*
+   * Returns TextAttribute object which has actual default attribute values
+   * (e.g. `foregroundColor = black`), in oppose to TextAttribute's default
+   * constructor which creates an object with nulled attributes.
+   */
+  static TextAttributes defaultTextAttributes();
+
 #pragma mark - Fields
 
   // Color

ReactCommon/fabric/components/text/paragraph/ParagraphShadowNode.cpp

@@ -16,8 +16,11 @@ const char ParagraphComponentName[] = "Paragraph";
 
 AttributedString ParagraphShadowNode::getAttributedString() const {
   if (!cachedAttributedString_.has_value()) {
+    auto textAttributes = TextAttributes::defaultTextAttributes();
+    textAttributes.apply(getProps()->textAttributes);
+
     cachedAttributedString_ = BaseTextShadowNode::getAttributedString(
-        getProps()->textAttributes, shared_from_this());
+        textAttributes, shared_from_this());
   }
 
   return cachedAttributedString_.value();