LibWeb: More work on width of position:absolute elements

The shrink-to-fit width algorithm actually works a little bit different
in the absolute positioning context, so it can't share all of its code
with non-absolute positioning.

Also, inline-block elements were always inserting unnecessary line
breaks when splitting, which caused the preferred width to be smaller
than it should be. This patch fixes that as well, by just not breaking
after inline-block elements in LayoutMode::OnlyRequiredLineBreaks.

2 files changed, 64 insertions, 25 deletions

diff --git a/Libraries/LibWeb/Layout/LayoutBlock.cpp b/Libraries/LibWeb/Layout/LayoutBlock.cpp
index 48cf803cde..e6da4528e0 100644
--- a/Libraries/LibWeb/Layout/LayoutBlock.cpp
+++ b/Libraries/LibWeb/Layout/LayoutBlock.cpp
@@ -282,22 +282,50 @@ void LayoutBlock::compute_width_for_absolutely_positioned_block()
     auto width = style.length_or_fallback(CSS::PropertyID::Width, {}, containing_block.width());
 
     auto solve_for_left = [&] {
-        left = Length(containing_block.width() - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this) - width.to_px(*this) - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this) - right.to_px(*this), Length::Type::Px);
+        return Length(containing_block.width() - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this) - width.to_px(*this) - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this) - right.to_px(*this), Length::Type::Px);
     };
 
     auto solve_for_width = [&] {
-        width = Length(containing_block.width() - left.to_px(*this) - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this) - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this) - right.to_px(*this), Length::Type::Px);
+        return Length(containing_block.width() - left.to_px(*this) - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this) - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this) - right.to_px(*this), Length::Type::Px);
     };
 
     auto solve_for_right = [&] {
-        left = Length(containing_block.width() - left.to_px(*this) - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this) - width.to_px(*this) - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this), Length::Type::Px);
+        return Length(containing_block.width() - left.to_px(*this) - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this) - width.to_px(*this) - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this), Length::Type::Px);
     };
 
+    // If all three of 'left', 'width', and 'right' are 'auto':
+    if (left.is_auto() && width.is_auto() && right.is_auto()) {
+        // First set any 'auto' values for 'margin-left' and 'margin-right' to 0.
+        if (margin_left.is_auto())
+            margin_left = Length(0, Length::Type::Px);
+        if (margin_right.is_auto())
+            margin_right = Length(0, Length::Type::Px);
+        // Then, if the 'direction' property of the element establishing the static-position containing block
+        // is 'ltr' set 'left' to the static position and apply rule number three below;
+        // otherwise, set 'right' to the static position and apply rule number one below.
+        // FIXME: This is very hackish.
+        left = Length(0, Length::Type::Px);
+        goto Rule3;
+    }
+
+    if (!left.is_auto() && !width.is_auto() && !right.is_auto()) {
+        // FIXME: This should be solved in a more complicated way.
+        set_width(width.to_px(*this));
+        return;
+    }
+
+    if (margin_left.is_auto())
+        margin_left = Length(0, Length::Type::Px);
+    if (margin_right.is_auto())
+        margin_right = Length(0, Length::Type::Px);
+
     // 1. 'left' and 'width' are 'auto' and 'right' is not 'auto',
     //    then the width is shrink-to-fit. Then solve for 'left'
     if (left.is_auto() && width.is_auto() && !right.is_auto()) {
-        width = Length(calculate_shrink_to_fit_width(margin_left, border_left, padding_left, padding_right, border_right, margin_right), Length::Type::Px);
+        auto result = calculate_shrink_to_fit_width();
         solve_for_left();
+        auto available_width = solve_for_width();
+        width = Length(min(max(result.preferred_minimum_width, available_width.to_px(*this)), result.preferred_width), Length::Type::Px);
     }
 
     // 2. 'left' and 'right' are 'auto' and 'width' is not 'auto',
@@ -309,29 +337,32 @@ void LayoutBlock::compute_width_for_absolutely_positioned_block()
         // FIXME: Check direction
         // FIXME: Use the static-position containing block
         left = zero_value;
-        solve_for_right();
+        right = solve_for_right();
     }
 
     // 3. 'width' and 'right' are 'auto' and 'left' is not 'auto',
     //    then the width is shrink-to-fit. Then solve for 'right'
     else if (width.is_auto() && right.is_auto() && !left.is_auto()) {
-        width = Length(calculate_shrink_to_fit_width(margin_left, border_left, padding_left, padding_right, border_right, margin_right), Length::Type::Px);
-        solve_for_right();
+    Rule3:
+        auto result = calculate_shrink_to_fit_width();
+        right = solve_for_right();
+        auto available_width = solve_for_width();
+        width = Length(min(max(result.preferred_minimum_width, available_width.to_px(*this)), result.preferred_width), Length::Type::Px);
     }
 
     // 4. 'left' is 'auto', 'width' and 'right' are not 'auto', then solve for 'left'
     else if (left.is_auto() && !width.is_auto() && !right.is_auto()) {
-        solve_for_left();
+        left = solve_for_left();
     }
 
     // 5. 'width' is 'auto', 'left' and 'right' are not 'auto', then solve for 'width'
     else if (width.is_auto() && !left.is_auto() && !right.is_auto()) {
-        solve_for_width();
+        width = solve_for_width();
     }
 
     // 6. 'right' is 'auto', 'left' and 'width' are not 'auto', then solve for 'right'
     else if (right.is_auto() && !left.is_auto() && !width.is_auto()) {
-        solve_for_right();
+        right = solve_for_right();
     }
 
     set_width(width.to_px(*this));
@@ -425,8 +456,20 @@ void LayoutBlock::compute_width()
                 margin_right = zero_value;
 
             // If 'width' is 'auto', the used value is the shrink-to-fit width as for floating elements.
-            if (width.is_auto())
-                width = Length(calculate_shrink_to_fit_width(margin_left, border_left, padding_left, padding_right, border_right, margin_right), Length::Type::Px);
+            if (width.is_auto()) {
+
+                // Find the available width: in this case, this is the width of the containing
+                // block minus the used values of 'margin-left', 'border-left-width', 'padding-left',
+                // 'padding-right', 'border-right-width', 'margin-right', and the widths of any relevant scroll bars.
+                float available_width = containing_block.width()
+                    - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this)
+                    - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this);
+
+                auto result = calculate_shrink_to_fit_width();
+
+                // Then the shrink-to-fit width is: min(max(preferred minimum width, available width), preferred width).
+                width = Length(min(max(result.preferred_minimum_width, available_width), result.preferred_width), Length::Type::Px);
+            }
         }
 
         return width;
@@ -489,7 +532,7 @@ void LayoutBlock::place_block_level_replaced_element_in_normal_flow(LayoutReplac
     box.set_offset(x, y);
 }
 
-float LayoutBlock::calculate_shrink_to_fit_width(const Length& margin_left, const Length& border_left, const Length& padding_left, const Length& padding_right, const Length& border_right, const Length& margin_right)
+LayoutBlock::ShrinkToFitResult LayoutBlock::calculate_shrink_to_fit_width()
 {
     auto greatest_child_width = [&] {
         float max_width = 0;
@@ -506,14 +549,6 @@ float LayoutBlock::calculate_shrink_to_fit_width(const Length& margin_left, cons
         return max_width;
     };
 
-    // Find the available width: in this case, this is the width of the containing
-    // block minus the used values of 'margin-left', 'border-left-width', 'padding-left',
-    // 'padding-right', 'border-right-width', 'margin-right', and the widths of any relevant scroll bars.
-
-    float available_width = containing_block()->width()
-        - margin_left.to_px(*this) - border_left.to_px(*this) - padding_left.to_px(*this)
-        - padding_right.to_px(*this) - border_right.to_px(*this) - margin_right.to_px(*this);
-
     // Calculate the preferred width by formatting the content without breaking lines
     // other than where explicit line breaks occur.
     layout_inside(LayoutMode::OnlyRequiredLineBreaks);
@@ -525,8 +560,7 @@ float LayoutBlock::calculate_shrink_to_fit_width(const Length& margin_left, cons
     layout_inside(LayoutMode::AllPossibleLineBreaks);
     float preferred_minimum_width = greatest_child_width();
 
-    // Then the shrink-to-fit width is: min(max(preferred minimum width, available width), preferred width).
-    return min(max(preferred_minimum_width, available_width), preferred_width);
+    return { preferred_width, preferred_minimum_width };
 }
 
 void LayoutBlock::place_block_level_non_replaced_element_in_normal_flow(LayoutBlock& block)
@@ -672,8 +706,9 @@ void LayoutBlock::split_into_lines(LayoutBlock& container, LayoutMode layout_mod
     layout(layout_mode);
 
     auto* line_box = &container.ensure_last_line_box();
-    if (line_box->width() > 0 && line_box->width() + width() > container.width())
+    if (layout_mode != LayoutMode::OnlyRequiredLineBreaks && line_box->width() > 0 && line_box->width() + width() > container.width()) {
         line_box = &container.add_line_box();
+    }
     line_box->add_fragment(*this, 0, 0, width(), height());
 }
 
diff --git a/Libraries/LibWeb/Layout/LayoutBlock.h b/Libraries/LibWeb/Layout/LayoutBlock.h
index 612e2b65b0..436c427255 100644
--- a/Libraries/LibWeb/Layout/LayoutBlock.h
+++ b/Libraries/LibWeb/Layout/LayoutBlock.h
@@ -73,7 +73,11 @@ protected:
 private:
     virtual bool is_block() const override { return true; }
 
-    float calculate_shrink_to_fit_width(const Length& margin_left, const Length& border_left, const Length& padding_left, const Length& padding_right, const Length& border_right, const Length& margin_right);
+    struct ShrinkToFitResult {
+        float preferred_width { 0 };
+        float preferred_minimum_width { 0 };
+    };
+    ShrinkToFitResult calculate_shrink_to_fit_width();
 
     void compute_width_for_absolutely_positioned_block();