Fix flex items losing their stretched cross size

Preserve the final cross-axis size assigned to auto-sized stretched flex
items when their block layout runs. Keep intrinsic flex measurement
separate so content changes can still update item sizing correctly.

Add an HTML regression test covering a short sidebar stretched alongside
taller content.

src/eepp/ui/blocklayouter.cpp

@@ -1,6 +1,7 @@
 #include <eepp/core/containers.hpp>
 #include <eepp/graphics/richtext.hpp>
 #include <eepp/ui/blocklayouter.hpp>
+#include <eepp/ui/flexlayouter.hpp>
 #include <eepp/ui/uihtmltable.hpp>
 #include <eepp/ui/uihtmlwidget.hpp>
 #include <eepp/ui/uirichtext.hpp>
@@ -10,13 +11,21 @@
 
 namespace EE { namespace UI {
 
-static bool isStretchedFlexItem( UIHTMLWidget* widget ) {
+static bool isStretchedFlexItemInAxis( UIHTMLWidget* widget, bool horizontalAxis ) {
 	Node* parent = widget->getParent();
 	if ( !parent || !parent->isWidget() || !parent->isType( UI_TYPE_HTML_WIDGET ) )
 		return false;
 	UIHTMLWidget* parentHtml = parent->asType<UIHTMLWidget>();
 	if ( !parentHtml->isFlex() )
 		return false;
+	if ( static_cast<FlexLayouter*>( parentHtml->getLayouter() )->isMeasuringItems() )
+		return false;
+
+	CSSFlexDirection direction = parentHtml->getFlexDirection();
+	bool crossAxisIsHorizontal =
+		direction == CSSFlexDirection::Column || direction == CSSFlexDirection::ColumnReverse;
+	if ( horizontalAxis != crossAxisIsHorizontal )
+		return false;
 
 	CSSAlignSelf alignSelf = widget->getAlignSelf();
 	if ( alignSelf == CSSAlignSelf::Stretch )
@@ -179,9 +188,11 @@ void BlockLayouter::updateLayout() {
 		}
 	}
 
-	if ( totW != mContainer->getPixelsSize().getWidth() ||
-		 ( mContainer->getLayoutWidthPolicy() == SizePolicy::WrapContent &&
-		   !isStretchedFlexItem( widget ) ) )
+	bool preserveStretchedWidth = mContainer->getLayoutWidthPolicy() == SizePolicy::WrapContent &&
+								  isStretchedFlexItemInAxis( widget, true );
+	if ( !preserveStretchedWidth &&
+		 ( totW != mContainer->getPixelsSize().getWidth() ||
+		   mContainer->getLayoutWidthPolicy() == SizePolicy::WrapContent ) )
 		mContainer->setInternalPixelsWidth( totW );
 
 	Float totH = mContainer->getPixelsSize().getHeight();
@@ -207,9 +218,11 @@ void BlockLayouter::updateLayout() {
 		}
 	}
 
-	if ( totH != mContainer->getPixelsSize().getHeight() ||
-		 ( mContainer->getLayoutHeightPolicy() == SizePolicy::WrapContent &&
-		   !isStretchedFlexItem( widget ) ) )
+	bool preserveStretchedHeight = mContainer->getLayoutHeightPolicy() == SizePolicy::WrapContent &&
+								   isStretchedFlexItemInAxis( widget, false );
+	if ( !preserveStretchedHeight &&
+		 ( totH != mContainer->getPixelsSize().getHeight() ||
+		   mContainer->getLayoutHeightPolicy() == SizePolicy::WrapContent ) )
 		mContainer->setInternalPixelsHeight( totH );
 
 	mContainer->endAttributesTransaction();

src/eepp/ui/flexlayouter.cpp

@@ -1223,8 +1223,8 @@ void FlexLayouter::updateLayout() {
 		return;
 
 	RichText* richText = widget->isType( UI_TYPE_RICHTEXT )
-									   ? widget->asType<UIRichText>()->getRichTextPtr()
-									   : nullptr;
+							 ? widget->asType<UIRichText>()->getRichTextPtr()
+							 : nullptr;
 	bool preserveFloatConstrainedBFCWidth =
 		widget->establishesBlockFormattingContext() &&
 		widget->getLayoutWidthPolicy() == SizePolicy::MatchParent && richText != nullptr &&
@@ -1387,6 +1387,7 @@ void FlexLayouter::updateLayout() {
 	bool indefiniteMainSize = ( mainAxis.horizontal && widthPolicy == SizePolicy::WrapContent ) ||
 							  ( !mainAxis.horizontal && heightPolicy == SizePolicy::WrapContent );
 
+	mMeasuringItems = true;
 	measureFlexItems( mainAxis, crossAxis, containerCrossSize, containerWidth, containerHeight,
 					  containerPadding, indefiniteMainSize, indefiniteCrossSize );
 
@@ -1410,6 +1411,7 @@ void FlexLayouter::updateLayout() {
 		alignMainAxis( line, containerMainSize, mColumnGap );
 		resolveCrossSizes( line, crossAxis, mainAxis );
 	}
+	mMeasuringItems = false;
 
 	alignCrossAxis( lines, containerCrossSize, mRowGap, crossAxis );
 

src/tests/unit_tests/uihtml_tests.cpp

@@ -5136,6 +5136,47 @@ UTEST( UIHTML, FlexLiItemsWrapContentWidth ) {
 	Engine::destroySingleton();
 }
 
+UTEST( UIHTML, FlexStretchPreservesAutoCrossSizeAfterChildLayout ) {
+	Engine::instance()->createWindow(
+		WindowSettings( 1024, 768, "Flex Stretch Auto Cross Size Test", WindowStyle::Default,
+						WindowBackend::Default, 32, {}, 1, false, true ),
+		ContextSettings( false, 0, 0, GLv_default, true, false ) );
+
+	UISceneNode* sceneNode = init_test_inline_block();
+	sceneNode->loadLayoutFromString( HTMLFormatter::HTMLtoXML( R"html(
+		<html><head><style>
+			.container { display: flex; width: 600px; }
+			.short { width: 200px; padding: 10px; }
+			.tall { width: 200px; height: 300px; }
+		</style></head><body>
+			<div class="container">
+				<aside class="short"><p>Short content</p></aside>
+				<main class="tall"></main>
+			</div>
+		</body></html>
+	)html" ) );
+
+	sceneNode->update( Seconds( 1 ) );
+	sceneNode->updateDirtyLayouts();
+
+	auto* containerNode = sceneNode->getRoot()->findByClass( "container" );
+	auto* shortItemNode = sceneNode->getRoot()->findByClass( "short" );
+	auto* tallItemNode = sceneNode->getRoot()->findByClass( "tall" );
+	ASSERT_TRUE( containerNode != nullptr );
+	ASSERT_TRUE( shortItemNode != nullptr );
+	ASSERT_TRUE( tallItemNode != nullptr );
+	auto* container = containerNode->asType<UIWidget>();
+	auto* shortItem = shortItemNode->asType<UIWidget>();
+	auto* tallItem = tallItemNode->asType<UIWidget>();
+
+	EXPECT_NEAR( container->getPixelsSize().getHeight(), tallItem->getPixelsSize().getHeight(),
+				 1.f );
+	EXPECT_NEAR( shortItem->getPixelsSize().getHeight(), tallItem->getPixelsSize().getHeight(),
+				 1.f );
+
+	Engine::destroySingleton();
+}
+
 UTEST( UIHTML, ImagePercentageWidthRespectsParentMaxWidth ) {
 	auto win = Engine::instance()->createWindow(
 		WindowSettings( 1024, 768, "img pct width respects parent max-width", WindowStyle::Default,