From 88ce8773272a577c11fc10baadef3fe2aac85845 Mon Sep 17 00:00:00 2001
From: Anna Powolny <apowolny@meta.com>
Date: Wed, 15 Jan 2025 08:06:10 -0800
Subject: [PATCH] Fix scroll stretching

Summary:
During the last QE where I was testing the Primitive scroll someone reported that the scroll is taking too much space.
https://fb.workplace.com/groups/litho.support/permalink/3981699508818054/

After investigating it, what seems to be wrong is again the measuring logic...

We tried to create a copy of [ViewGroup.getChildMeasureSpec](https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/view/ViewGroup.java#7030)
but I didn't include the specMode variants.

Before the change:
**Spec:** widthSpec from spec **[1080, AT_MOST]**
**Primitive:**
- sizeConstraints width mode **AT_MOST** SizeConstraints[**minWidth = 0, maxWidth = 1080**, minHeight = 0, maxHeight = 1647] (what we are getting in LayoutScope.layout)
- childConstraints width **[1080, EXACTLY]**  SizeConstraints **[minWidth = 1080, maxWidth = 1080**, minHeight = 0, maxHeight = Infinity] (this is the result of our getChildMeasureSpec primitive call)

I published next diff with force to test and let's see if all of the e2e and tests will pass
<fingers crossed>

Reviewed By: adityasharat

Differential Revision: D68208796

fbshipit-source-id: a3f054da61afaaad451ad7577d5a115fce0fad65
---
 .../widget/ExperimentalVerticalScroll.kt      | 25 +++++++++++++++----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/litho-widget/src/main/java/com/facebook/litho/widget/ExperimentalVerticalScroll.kt b/litho-widget/src/main/java/com/facebook/litho/widget/ExperimentalVerticalScroll.kt
index 0f4fa02975..3a11afd39d 100644
--- a/litho-widget/src/main/java/com/facebook/litho/widget/ExperimentalVerticalScroll.kt
+++ b/litho-widget/src/main/java/com/facebook/litho/widget/ExperimentalVerticalScroll.kt
@@ -44,6 +44,8 @@ import com.facebook.rendercore.primitives.LayoutBehavior
 import com.facebook.rendercore.primitives.LayoutScope
 import com.facebook.rendercore.primitives.PrimitiveLayoutResult
 import com.facebook.rendercore.primitives.ViewAllocator
+import com.facebook.rendercore.toWidthSpec
+import com.facebook.rendercore.utils.MeasureSpecUtils.getMode
 import kotlin.math.max
 import kotlin.math.min
 
@@ -227,9 +229,11 @@ internal class VerticalScrollLayoutBehavior(
 
     val (minMeasureWidth, maxMeasureWidth) =
         getChildMeasureSize(
-            constraints.minWidth, constraints.maxWidth, ViewGroup.LayoutParams.MATCH_PARENT)
+            constraints.minWidth,
+            constraints.maxWidth,
+            ViewGroup.LayoutParams.MATCH_PARENT,
+            getMode(sizeConstraints.toWidthSpec()))
     val childConstraints = constraints.copy(minWidth = minMeasureWidth, maxWidth = maxMeasureWidth)
-
     val layoutState =
         NestedLithoTree.layout(
             result = resolveResult,
@@ -262,7 +266,12 @@ internal class VerticalScrollLayoutBehavior(
   /**
    * Equivalent to [VerticalScrollComponent.onMeasure] code calling [ViewGroup.getChildMeasureSpec]
    */
-  private fun getChildMeasureSize(min: Int, max: Int, preferred: Int): Pair<Int, Int> =
+  private fun getChildMeasureSize(
+      min: Int,
+      max: Int,
+      preferred: Int,
+      widthMode: Int
+  ): Pair<Int, Int> =
       when {
         preferred >= 0 || min == max -> {
           // Fixed size due to fixed size layout param or fixed constraints.
@@ -274,8 +283,14 @@ internal class VerticalScrollLayoutBehavior(
           0 to max
         }
         preferred == ViewGroup.LayoutParams.MATCH_PARENT && max != SizeConstraints.Infinity -> {
-          // Match parent layout param, so we force the child to fill the available space.
-          max to max
+          if (widthMode == View.MeasureSpec.AT_MOST) {
+            // Match parent layout param with AT_MOST constraint, so we let the child decide its
+            // size.
+            0 to max
+          } else {
+            // Match parent layout param, so we force the child to fill the available space.
+            max to max
+          }
         }
         else -> {
           // max constraint is infinite and layout param is WRAP_CONTENT or MATCH_PARENT.