LibWeb: Serialize grid-area as auto if all sub-properties are auto

Author: https://github.com/tcl3
Commit: https://github.com/LadybirdBrowser/ladybird/commit/c029a9c98c9
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4004
Reviewed-by: https://github.com/AtkinsSJ ✅

Libraries/LibWeb/CSS/StyleValues/ShorthandStyleValue.cpp

@@ -293,6 +293,8 @@ String ShorthandStyleValue::to_string(SerializationMode mode) const
             builder.appendff(" / {}", row_end.grid_track_placement().to_string());
         if (!column_end.grid_track_placement().is_auto())
             builder.appendff(" / {}", column_end.grid_track_placement().to_string());
+        if (builder.is_empty())
+            return "auto"_string;
         return MUST(builder.to_string());
     }
         // FIXME: Serialize Grid differently once we support it better!

Tests/LibWeb/Text/expected/css/CSSStyleProperties-all-supported-properties-and-default-values.txt

@@ -366,8 +366,8 @@ All supported properties and their default values exposed from CSSStylePropertie
 'font-width': 'normal'
 'gap': 'normal'
 'grid': ''
-'gridArea': ''
-'grid-area': ''
+'gridArea': 'auto'
+'grid-area': 'auto'
 'gridAutoColumns': 'auto'
 'grid-auto-columns': 'auto'
 'gridAutoFlow': 'row'

Tests/LibWeb/Text/expected/wpt-import/css/css-grid/parsing/grid-area-computed.txt

@@ -2,9 +2,9 @@ Harness status: OK
 
 Found 30 tests
 
-13 Pass
-17 Fail
-Fail	Property grid-area value 'auto / auto / auto / auto'
+14 Pass
+16 Fail
+Pass	Property grid-area value 'auto / auto / auto / auto'
 Pass	Property grid-row value 'auto / auto'
 Pass	Property grid-column-end value 'auto'
 Fail	Property grid-row value '-zπ'

Tests/LibWeb/Text/expected/wpt-import/css/css-grid/parsing/grid-area-valid.txt

@@ -2,13 +2,13 @@ Harness status: OK
 
 Found 57 tests
 
-19 Pass
-38 Fail
-Fail	e.style['grid-area'] = "auto" should set the property value
-Fail	e.style['grid-area'] = "auto / auto" should set the property value
-Fail	e.style['grid-area'] = "auto / auto / auto" should set the property value
-Fail	e.style['grid-area'] = "auto / auto / auto / auto" should set the property value
-Fail	e.style['grid-area'] = "AuTo" should set the property value
+24 Pass
+33 Fail
+Pass	e.style['grid-area'] = "auto" should set the property value
+Pass	e.style['grid-area'] = "auto / auto" should set the property value
+Pass	e.style['grid-area'] = "auto / auto / auto" should set the property value
+Pass	e.style['grid-area'] = "auto / auto / auto / auto" should set the property value
+Pass	e.style['grid-area'] = "AuTo" should set the property value
 Pass	e.style['grid-row'] = "auto" should set the property value
 Pass	e.style['grid-row'] = "auto/auto" should set the property value
 Pass	e.style['grid-column-end'] = "AuTo" should set the property value