Fix Android Text measured one line taller than drawn at fractional widths

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/views/text/TextLayoutManager.kt

@@ -883,15 +883,19 @@ internal object TextLayoutManager {
     // Layout.getDesiredWidth is a full measuring pass over the text, so only run it when its
     // result can affect the layout width. It cannot when the width is EXACTLY, nor when the text
     // was boring but did not fit: boring.width is the unwrapped width of the same text and we only
-    // get here if it exceeds floor(width), so min(desiredWidth, floor(width)) is floor(width).
+    // get here if it exceeds floor(width), so min(desiredWidth, ceil(width)) is ceil(width).
+    //
+    // AT_MOST wraps at ceil(width), the same width EXACTLY uses when the text is drawn. Wrapping at
+    // floor(width) here measured text that fits in (floor(width), width] as one line more than it
+    // is drawn with. calculateWidth() clamps the reported width to the AT_MOST constraint.
     val layoutWidth =
         when {
           widthYogaMeasureMode == YogaMeasureMode.EXACTLY -> ceil(width).toInt()
-          widthYogaMeasureMode == YogaMeasureMode.AT_MOST && boring != null -> floor(width).toInt()
+          widthYogaMeasureMode == YogaMeasureMode.AT_MOST && boring != null -> ceil(width).toInt()
           else -> {
             val desiredWidth = ceil(Layout.getDesiredWidth(text, paint)).toInt()
             if (widthYogaMeasureMode == YogaMeasureMode.AT_MOST) {
-              min(desiredWidth, floor(width).toInt())
+              min(desiredWidth, ceil(width).toInt())
             } else {
               desiredWidth
             }
@@ -1708,6 +1712,11 @@ internal object TextLayoutManager {
       return width
     }
 
+    // The layout may be up to a subpixel wider than an AT_MOST width, see createLayout().
+    if (widthYogaMeasureMode == YogaMeasureMode.AT_MOST) {
+      return min(layout.width.toFloat(), width)
+    }
+
     return layout.width.toFloat()
   }
 

packages/react-native/ReactAndroid/src/test/java/com/facebook/react/views/text/TextLayoutManagerAtMostFractionalWidthTest.kt

@@ -0,0 +1,64 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+package com.facebook.react.views.text
+
+import android.annotation.SuppressLint
+import android.text.BoringLayout
+import android.text.Layout
+import android.text.SpannableString
+import android.text.TextPaint
+import com.facebook.yoga.YogaMeasureMode
+import kotlin.math.floor
+import org.assertj.core.api.Assertions.assertThat
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.robolectric.RobolectricTestRunner
+import org.robolectric.annotation.GraphicsMode
+
+@RunWith(RobolectricTestRunner::class)
+@GraphicsMode(GraphicsMode.Mode.NATIVE)
+class TextLayoutManagerAtMostFractionalWidthTest {
+
+  @Test
+  fun `AT_MOST measure and EXACTLY draw at the same fractional width have the same line count`() {
+    val text = SpannableString("Keep watching this text")
+    val paint = TextPaint(TextPaint.ANTI_ALIAS_FLAG).apply { textSize = 16f }
+    val desiredWidth = Layout.getDesiredWidth(text, paint)
+    // A width the text fits in, but whose floor is smaller than the text.
+    val width = floor(desiredWidth) + (desiredWidth - floor(desiredWidth) + 1f) / 2f
+    assertThat(floor(width)).isLessThan(desiredWidth)
+    assertThat(width).isGreaterThanOrEqualTo(desiredWidth)
+
+    val measured = invokeCreateLayout(text, width, YogaMeasureMode.AT_MOST, paint)
+    val drawn = invokeCreateLayout(text, width, YogaMeasureMode.EXACTLY, paint)
+
+    assertThat(measured.lineCount).isEqualTo(drawn.lineCount)
+  }
+
+  @SuppressLint("InlinedApi")
+  private fun invokeCreateLayout(
+      text: SpannableString,
+      width: Float,
+      mode: YogaMeasureMode,
+      paint: TextPaint,
+  ): Layout =
+      TextLayoutManager.createLayout(
+          text,
+          BoringLayout.isBoring(text, paint),
+          width,
+          mode,
+          /* includeFontPadding = */ false,
+          /* textBreakStrategy = */ Layout.BREAK_STRATEGY_HIGH_QUALITY,
+          /* hyphenationFrequency = */ Layout.HYPHENATION_FREQUENCY_NONE,
+          Layout.Alignment.ALIGN_NORMAL,
+          /* justificationMode = */ 0,
+          /* ellipsizeMode = */ null,
+          /* maxNumberOfLines = */ 2,
+          paint,
+      )
+}