LibWeb: Use resolve_grid_position if row and column are definite in GFC

With this change we use the same code to resolve (start, end, span)
based on computed values in all cases:
- When only column is definite
- When only row is definite
- When both are definite

Userland/Libraries/LibWeb/Layout/GridFormattingContext.cpp

@@ -215,144 +215,13 @@ GridFormattingContext::PlacementPosition GridFormattingContext::resolve_grid_pos
 
 void GridFormattingContext::place_item_with_row_and_column_position(Box const& child_box)
 {
-    auto const& grid_row_start = child_box.computed_values().grid_row_start();
-    auto const& grid_row_end = child_box.computed_values().grid_row_end();
-    auto const& grid_column_start = child_box.computed_values().grid_column_start();
-    auto const& grid_column_end = child_box.computed_values().grid_column_end();
-
-    int row_start = 0, row_end = 0, column_start = 0, column_end = 0;
-
-    if (grid_row_start.has_line_number())
-        row_start = child_box.computed_values().grid_row_start().line_number() - 1;
-    if (grid_row_end.has_line_number())
-        row_end = child_box.computed_values().grid_row_end().line_number() - 1;
-    if (grid_column_start.has_line_number())
-        column_start = child_box.computed_values().grid_column_start().line_number() - 1;
-    if (grid_column_end.has_line_number())
-        column_end = child_box.computed_values().grid_column_end().line_number() - 1;
-
-    // https://www.w3.org/TR/css-grid-2/#line-placement
-    // 8.3. Line-based Placement: the grid-row-start, grid-column-start, grid-row-end, and grid-column-end properties
-
-    // https://www.w3.org/TR/css-grid-2/#grid-placement-slot
-    // First attempt to match the grid area’s edge to a named grid area: if there is a grid line whose
-    // line name is <custom-ident>-start (for grid-*-start) / <custom-ident>-end (for grid-*-end),
-    // contributes the first such line to the grid item’s placement.
-
-    // Otherwise, treat this as if the integer 1 had been specified along with the <custom-ident>.
-
-    // https://www.w3.org/TR/css-grid-2/#grid-placement-int
-    // Contributes the Nth grid line to the grid item’s placement. If a negative integer is given, it
-    // instead counts in reverse, starting from the end edge of the explicit grid.
-    if (row_end < 0)
-        row_end = m_occupation_grid.row_count() + row_end + 2;
-    if (column_end < 0)
-        column_end = m_occupation_grid.column_count() + column_end + 2;
-
-    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
-    // lines with that name exist, all implicit grid lines are assumed to have that name for the purpose
-    // of finding this position.
-
-    // https://www.w3.org/TR/css-grid-2/#grid-placement-span-int
-    // Contributes a grid span to the grid item’s placement such that the corresponding edge of the grid
-    // item’s grid area is N lines from its opposite edge in the corresponding direction. For example,
-    // grid-column-end: span 2 indicates the second grid line in the endward direction from the
-    // grid-column-start line.
-    size_t row_span = 1;
-    size_t column_span = 1;
-    if (grid_row_start.has_line_number() && grid_row_end.is_span())
-        row_span = grid_row_end.span();
-    if (grid_column_start.has_line_number() && grid_column_end.is_span())
-        column_span = grid_column_end.span();
-    if (grid_row_end.has_line_number() && child_box.computed_values().grid_row_start().is_span()) {
-        row_span = grid_row_start.span();
-        row_start = row_end - row_span;
-    }
-    if (grid_column_end.has_line_number() && grid_column_start.is_span()) {
-        column_span = grid_column_start.span();
-        column_start = column_end - column_span;
-    }
-
-    // If a name is given as a <custom-ident>, only lines with that name are counted. If not enough
-    // lines with that name exist, all implicit grid lines on the side of the explicit grid
-    // corresponding to the search direction are assumed to have that name for the purpose of counting
-    // this span.
-
-    // https://drafts.csswg.org/css-grid/#grid-placement-auto
-    // auto
-    // The property contributes nothing to the grid item’s placement, indicating auto-placement or a
-    // default span of one. (See § 8 Placing Grid Items, above.)
-
-    // https://www.w3.org/TR/css-grid-2/#common-uses-named-lines
-    // 8.1.3. Named Lines and Spans
-    // Instead of counting lines by number, lines can be referenced by their line name:
-    if (grid_column_end.has_identifier()) {
-        if (auto maybe_grid_area = m_grid_areas.get(grid_column_end.identifier()); maybe_grid_area.has_value())
-            column_end = maybe_grid_area->column_end;
-        else if (auto line_name_index = get_line_index_by_line_name(GridDimension::Column, grid_column_end.identifier()); line_name_index.has_value())
-            column_end = line_name_index.value();
-        else
-            column_end = 1;
-        column_start = column_end - 1;
-    }
-
-    if (grid_column_start.has_identifier()) {
-        if (auto maybe_grid_area = m_grid_areas.get(grid_column_start.identifier()); maybe_grid_area.has_value())
-            column_start = maybe_grid_area->column_start;
-        else if (auto line_name_index = get_line_index_by_line_name(GridDimension::Column, grid_column_start.identifier()); line_name_index.has_value())
-            column_start = line_name_index.value();
-        else
-            column_start = 0;
-    }
-
-    if (grid_row_end.has_identifier()) {
-        if (auto maybe_grid_area = m_grid_areas.get(grid_row_end.identifier()); maybe_grid_area.has_value())
-            row_end = maybe_grid_area->row_end;
-        else if (auto line_name_index = get_line_index_by_line_name(GridDimension::Row, grid_row_end.identifier()); line_name_index.has_value())
-            row_end = line_name_index.value();
-        else
-            row_end = 1;
-        row_start = row_end - 1;
-    }
-
-    if (grid_row_start.has_identifier()) {
-        if (auto maybe_grid_area = m_grid_areas.get(grid_row_start.identifier()); maybe_grid_area.has_value())
-            row_start = maybe_grid_area->row_start;
-        else if (auto line_name_index = get_line_index_by_line_name(GridDimension::Row, grid_row_start.identifier()); line_name_index.has_value())
-            row_start = line_name_index.value();
-        else
-            row_start = 0;
-    }
-
-    // If there are multiple lines of the same name, they effectively establish a named set of grid
-    // lines, which can be exclusively indexed by filtering the placement by name:
-
-    // https://drafts.csswg.org/css-grid/#grid-placement-errors
-    // 8.3.1. Grid Placement Conflict Handling
-    // If the placement for a grid item contains two lines, and the start line is further end-ward than
-    // the end line, swap the two lines. If the start line is equal to the end line, remove the end
-    // line.
-    if (grid_row_start.is_positioned() && grid_row_end.is_positioned()) {
-        if (row_start > row_end)
-            swap(row_start, row_end);
-        if (row_start != row_end)
-            row_span = row_end - row_start;
-    }
-    if (grid_column_start.is_positioned() && grid_column_end.is_positioned()) {
-        if (column_start > column_end)
-            swap(column_start, column_end);
-        if (column_start != column_end)
-            column_span = column_end - column_start;
-    }
-
-    // If the placement contains two spans, remove the one contributed by the end grid-placement
-    // property.
-    if (grid_row_start.is_span() && grid_row_end.is_span())
-        row_span = grid_row_start.span();
-    if (grid_column_start.is_span() && grid_column_end.is_span())
-        column_span = grid_column_start.span();
+    auto row_placement_position = resolve_grid_position(child_box, GridDimension::Row);
+    auto column_placement_position = resolve_grid_position(child_box, GridDimension::Column);
 
-    // FIXME: If the placement contains only a span for a named line, replace it with a span of 1.
+    auto row_start = row_placement_position.start;
+    auto row_span = row_placement_position.span;
+    auto column_start = column_placement_position.start;
+    auto column_span = column_placement_position.span;
 
     m_grid_items.append(GridItem {
         .box = child_box,