Extend Text to support measurement of empty Texts

Summary:
This diff extends the measurement of Text components in order to support empty strings.
This is required for parity with Paper.
I created a follow up task to analyze support of empty string as part of the Text infrastructure of Fabric in the future.

changelog: [Internal]

Reviewed By: sammy-SC

Differential Revision: D21761171

fbshipit-source-id: d2aa074052b09732af5d35723f19014090fcabbf

ReactAndroid/src/main/java/com/facebook/react/views/text/TextLayoutManager.java

@@ -20,6 +20,7 @@ import android.text.StaticLayout;
 import android.text.TextPaint;
 import android.util.LayoutDirection;
 import android.util.LruCache;
+import android.view.View;
 import androidx.annotation.Nullable;
 import com.facebook.common.logging.FLog;
 import com.facebook.react.bridge.ReadableArray;
@@ -86,7 +87,7 @@ public class TextLayoutManager {
       sb.append(TextTransform.apply(fragment.getString("string"), textAttributes.mTextTransform));
 
       int end = sb.length();
-      int reactTag = fragment.getInt("reactTag");
+      int reactTag = fragment.hasKey("reactTag") ? fragment.getInt("reactTag") : View.NO_ID;
       if (fragment.hasKey(ViewProps.IS_ATTACHMENT)
           && fragment.getBoolean(ViewProps.IS_ATTACHMENT)) {
         float width = PixelUtil.toPixelFromSP(fragment.getDouble(ViewProps.WIDTH));

ReactCommon/fabric/components/text/basetext/BaseTextShadowNode.h

@@ -57,6 +57,13 @@ class BaseTextShadowNode {
       ShadowNode const &parentNode,
       AttributedString &outAttributedString,
       Attachments &outAttachments);
+
+  /**
+   * Returns a character used to measure empty strings in native platforms.
+   */
+  inline static std::string getEmptyPlaceholder() {
+    return "I";
+  }
 };
 
 } // namespace react

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

@@ -120,13 +120,21 @@ Size ParagraphShadowNode::measure(LayoutConstraints layoutConstraints) const {
   auto content =
       getContentWithMeasuredAttachments(LayoutContext{}, layoutConstraints);
 
-  if (content.attributedString.isEmpty()) {
-    return layoutConstraints.clamp({0, 0});
+  auto attributedString = content.attributedString;
+  if (attributedString.isEmpty()) {
+    // Note: `zero-width space` is insufficient in some cases (e.g. when we need
+    // to measure the "height" of the font).
+    // TODO T67606511: We will redefine the measurement of empty strings as part
+    // of T67606511
+    auto string = BaseTextShadowNode::getEmptyPlaceholder();
+    auto textAttributes = TextAttributes::defaultTextAttributes();
+    textAttributes.apply(getConcreteProps().textAttributes);
+    attributedString.appendFragment({string, textAttributes, {}});
   }
 
   return textLayoutManager_
       ->measure(
-          AttributedStringBox{content.attributedString},
+          AttributedStringBox{attributedString},
           content.paragraphAttributes,
           layoutConstraints)
       .size;

ReactCommon/fabric/components/textinput/androidtextinput/AndroidTextInputShadowNode.cpp

@@ -62,6 +62,8 @@ AttributedString AndroidTextInputShadowNode::getAttributedString() const {
 // single character in the string so that the measured height is greater
 // than zero. Otherwise, empty TextInputs with no placeholder don't
 // display at all.
+// TODO T67606511: We will redefine the measurement of empty strings as part
+// of T67606511
 AttributedString AndroidTextInputShadowNode::getPlaceholderAttributedString()
     const {
   // Return placeholder text, since text and children are empty.
@@ -70,7 +72,7 @@ AttributedString AndroidTextInputShadowNode::getPlaceholderAttributedString()
   fragment.string = getConcreteProps().placeholder;
 
   if (fragment.string.empty()) {
-    fragment.string = " ";
+    fragment.string = BaseTextShadowNode::getEmptyPlaceholder();
   }
 
   auto textAttributes = TextAttributes::defaultTextAttributes();

ReactCommon/fabric/components/textinput/iostextinput/TextInputShadowNode.cpp

@@ -38,7 +38,11 @@ AttributedStringBox TextInputShadowNode::attributedStringBoxToMeasure() const {
     auto placeholder = getConcreteProps().placeholder;
     // Note: `zero-width space` is insufficient in some cases (e.g. when we need
     // to measure the "hight" of the font).
-    auto string = !placeholder.empty() ? placeholder : "I";
+    // TODO T67606511: We will redefine the measurement of empty strings as part
+    // of T67606511
+    auto string = !placeholder.empty()
+        ? placeholder
+        : BaseTextShadowNode::getEmptyPlaceholder();
     auto textAttributes = getConcreteProps().getEffectiveTextAttributes();
     attributedString.appendFragment({string, textAttributes, {}});
   }