Partial Mitigation for Samsung TextInput Hangs

Summary:
In facebook#35936 we observed that the presence of AbsoluteSizeSpan may lead to hangs when using the Grammarly keyboard on Samsung.

This mitigation makes it so that we do not emit this span in the most common cases, when it is sufficient to set `android:textSize`. In simple cases, it causes typing into the TextInput to no longer hang.

This does not resolve the issue for TextInputs which meaningfully use layout-effecting spans (or at least font size), such as non-uniform text size within the input. We could potentially do further work to reduce the number of spans emitted in these scenarios, but this may be fighting a losing battle against the platform.

Changelog:
[Android][Fixed] - Partial Mitigation for Samsung TextInput Hangs (Paper)

Reviewed By: cortinico

Differential Revision: D42721684

fbshipit-source-id: 5599070f10a385c6063683e3ac7a5acbbdc10ae9

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

@@ -308,6 +308,9 @@ protected Spannable spannedFromShadowNode(
       priority++;
     }
 
+    // Mitigation for https://github.com/facebook/react-native/issues/35936 (S318090)
+    flattenAbsoluteSizeSpans(sb);
+
     textShadowNode.mTextAttributes.setHeightOfTallestInlineViewOrImage(
         heightOfTallestInlineViewOrImage);
 
@@ -318,6 +321,29 @@ protected Spannable spannedFromShadowNode(
     return sb;
   }
 
+  private void flattenAbsoluteSizeSpans(SpannableStringBuilder sb) {
+    // If spans cover the entire input with the same size as
+    // getEffectiveFontSize() we can omit them
+    ReactAbsoluteSizeSpan[] spans = sb.getSpans(0, sb.length(), ReactAbsoluteSizeSpan.class);
+
+    int lastSpanIndex = -1;
+    final int expectedTextSize = mTextAttributes.getEffectiveFontSize();
+
+    for (ReactAbsoluteSizeSpan span : spans) {
+      if (sb.getSpanStart(span) > lastSpanIndex + 1 || span.getSize() != expectedTextSize) {
+        return;
+      }
+
+      lastSpanIndex = sb.getSpanEnd(span) - 1;
+    }
+
+    if (lastSpanIndex >= sb.length() - 1) {
+      for (ReactAbsoluteSizeSpan span : spans) {
+        sb.removeSpan(span);
+      }
+    }
+  }
+
   protected TextAttributes mTextAttributes;
 
   protected boolean mIsColorSet = false;

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

@@ -73,6 +73,16 @@ public long measure(
                   mPreparedSpannableText,
                   "Spannable element has not been prepared in onBeforeLayout");
 
+          // Unflatten AbsoluteSizeSpan for measurement (see flattenAbsoluteSizeSpans() in
+          // ReactBaseTextShadowNode)
+          if (text.getSpans(0, text.length(), ReactAbsoluteSizeSpan.class).length == 0) {
+            text.setSpan(
+                new ReactAbsoluteSizeSpan(mTextAttributes.getEffectiveFontSize()),
+                0,
+                text.length(),
+                Spannable.SPAN_INCLUSIVE_INCLUSIVE);
+          }
+
           Layout layout = measureSpannedText(text, width, widthMode);
 
           if (mAdjustsFontSizeToFit) {