LibWeb: Fix height computation (again) :^)

Height computation algorithm is actually
different for absolutely positioned boxes
and block formatting contexts (where it doesn't include floats)
Fixes #6408

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp

@@ -247,6 +247,49 @@ void BlockFormattingContext::compute_width_for_block_level_replaced_element_in_n
     box.set_width(compute_width_for_replaced_element(box));
 }
 
+static float compute_auto_height_for_block_level_element(const Box& box)
+{
+    Optional<float> top;
+    Optional<float> bottom;
+
+    if (box.children_are_inline()) {
+        // If it only has inline-level children, the height is the distance between
+        // the top of the topmost line box and the bottom of the bottommost line box.
+        if (!box.line_boxes().is_empty()) {
+            for (auto& fragment : box.line_boxes().first().fragments()) {
+                if (!top.has_value() || fragment.offset().y() < top.value())
+                    top = fragment.offset().y();
+            }
+            for (auto& fragment : box.line_boxes().last().fragments()) {
+                if (!bottom.has_value() || (fragment.offset().y() + fragment.height()) > bottom.value())
+                    bottom = fragment.offset().y() + fragment.height();
+            }
+        }
+    } else {
+        // If it has block-level children, the height is the distance between
+        // the top margin-edge of the topmost block-level child box
+        // and the bottom margin-edge of the bottommost block-level child box.
+        box.for_each_child_of_type<Box>([&](Layout::Box& child_box) {
+            if (child_box.is_absolutely_positioned())
+                return IterationDecision::Continue;
+            if ((box.computed_values().overflow_y() == CSS::Overflow::Visible) && child_box.is_floating())
+                return IterationDecision::Continue;
+
+            float child_box_top = child_box.effective_offset().y() - child_box.box_model().margin_box().top;
+            float child_box_bottom = child_box.effective_offset().y() + child_box.height() + child_box.box_model().margin_box().bottom;
+
+            if (!top.has_value() || child_box_top < top.value())
+                top = child_box_top;
+
+            if (!bottom.has_value() || child_box_bottom > bottom.value())
+                bottom = child_box_bottom;
+
+            return IterationDecision::Continue;
+        });
+    }
+    return bottom.value_or(0) - top.value_or(0);
+}
+
 void BlockFormattingContext::compute_height(Box& box)
 {
     auto& computed_values = box.computed_values();

Userland/Libraries/LibWeb/Layout/FormattingContext.cpp

@@ -160,7 +160,7 @@ static Gfx::FloatSize solve_replaced_size_constraint(float w, float h, const Rep
     return { w, h };
 }
 
-float FormattingContext::compute_auto_height_for_block_level_element(const Box& box)
+static float compute_auto_height_for_block_level_element(const Box& box)
 {
     Optional<float> top;
     Optional<float> bottom;

Userland/Libraries/LibWeb/Layout/FormattingContext.h

@@ -38,7 +38,6 @@ protected:
         float preferred_minimum_width { 0 };
     };
 
-    static float compute_auto_height_for_block_level_element(const Box& box);
     static float tentative_width_for_replaced_element(const ReplacedBox&, const CSS::Length& width);
     static float tentative_height_for_replaced_element(const ReplacedBox&, const CSS::Length& width);