Ship lazy layout for exact measurements

Summary:
This is part of the fix for android's double measure bug. It postpones ComponentLayout calculation from measure to layout is the measured dimensions are exact: this means that if we get remeasured with different exact measurements, we don't compute two layouts.

Deltoid results: https://fburl.com/deltoid3/ylrbxcpu (big-ish improvements for watch tab, small improvements for groups mall)

Reviewed By: IanChilds

Differential Revision: D8434171

fbshipit-source-id: 85b5c9aa2abd960d264071d6d358ecbbb6e50c78

litho-core/src/main/java/com/facebook/litho/LithoView.java

@@ -291,14 +291,15 @@ protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
       mTemporaryDetachedComponent = null;
     }
 
-    if (ComponentsConfiguration.lazyLayoutForExactSpec) {
-      if (!mForceLayout
-          && SizeSpec.getMode(widthMeasureSpec) == SizeSpec.EXACTLY
-          && SizeSpec.getMode(heightMeasureSpec) == SizeSpec.EXACTLY) {
-        mDoMeasureInLayout = true;
-        setMeasuredDimension(width, height);
-        return;
-      }
+    if (!mForceLayout
+        && SizeSpec.getMode(widthMeasureSpec) == SizeSpec.EXACTLY
+        && SizeSpec.getMode(heightMeasureSpec) == SizeSpec.EXACTLY) {
+      // If the measurements are exact, postpone LayoutState calculation from measure to layout.
+      // This is part of the fix for android's double measure bug. Doing this means that if we get
+      // remeasured with different exact measurements, we don't compute two layouts.
+      mDoMeasureInLayout = true;
+      setMeasuredDimension(width, height);
+      return;
     }
 
     mIsMeasuring = true;

litho-core/src/main/java/com/facebook/litho/config/ComponentsConfiguration.java

@@ -172,12 +172,6 @@ public class ComponentsConfiguration {
   /** Default for ComponentHost#hasOverlappingRendering. */
   public static boolean hostHasOverlappingRendering = true;
 
-  /**
-   * Don't compute LayoutState in LithoView#onMeasure if measure specs are exact: wait for onLayout
-   * instead.
-   */
-  public static boolean lazyLayoutForExactSpec = false;
-
   /** Enable variable BatchSize for ArrayBatchAllocator */
   public static boolean variableArrayBatchAllocatorEnabled = false;
 

litho-it/src/test/java/com/facebook/litho/LithoViewTest.java

@@ -76,7 +76,6 @@ protected Component onCreateLayout(ComponentContext c) {
   @After
   public void tearDown() {
     ComponentsConfiguration.doubleMeasureCorrection = false;
-    ComponentsConfiguration.lazyLayoutForExactSpec = false;
     ComponentsConfiguration.isDebugModeEnabled = ComponentsConfiguration.IS_INTERNAL_BUILD;
   }
 
@@ -278,23 +277,8 @@ public void testNoCorrectionWithConfigOff() {
     assertThat(mLithoView.getMeasuredHeight()).isEqualTo(100);
   }
 
-  @Test
-  public void testMeasureComputesLayoutStateWhenSpecsAreExactNotInConfig() {
-    ComponentsConfiguration.lazyLayoutForExactSpec = false;
-
-    mLithoView = new LithoView(RuntimeEnvironment.application);
-    mLithoView.setComponent(TestDrawableComponent.create(mLithoView.getComponentContext()).build());
-    mLithoView.measure(makeMeasureSpec(100, EXACTLY), makeMeasureSpec(100, EXACTLY));
-
-    assertThat(mLithoView.getMeasuredWidth()).isEqualTo(100);
-    assertThat(mLithoView.getMeasuredHeight()).isEqualTo(100);
-    assertThat(mLithoView.getComponentTree().getMainThreadLayoutState()).isNotNull();
-  }
-
   @Test
   public void testMeasureDoesNotComputeLayoutStateWhenSpecsAreExact() {
-    ComponentsConfiguration.lazyLayoutForExactSpec = true;
-
     mLithoView = new LithoView(RuntimeEnvironment.application);
     mLithoView.setComponent(TestDrawableComponent.create(mLithoView.getComponentContext()).build());
     mLithoView.measure(makeMeasureSpec(100, EXACTLY), makeMeasureSpec(100, EXACTLY));
@@ -312,8 +296,6 @@ public void testMeasureDoesNotComputeLayoutStateWhenSpecsAreExact() {
 
   @Test
   public void testMeasureComputesLayoutStateWhenSpecsAreNotExact() {
-    ComponentsConfiguration.lazyLayoutForExactSpec = true;
-
     mLithoView = new LithoView(RuntimeEnvironment.application);
     mLithoView.setComponent(
         TestDrawableComponent.create(mLithoView.getComponentContext()).heightPx(100).build());