Refactor GetAttr to fix attribute handling

Restructure the attribute creation logic in GetAttr to properly handle
the combination of URL editor cells and variant highlighting. The
previous code had issues where it would modify the shared URL editor
attribute or fail to properly merge column attributes in some cases.

The new approach collects the needed attributes first, then creates
the appropriate attribute object based on what is needed. This ensures
URL editor attributes are cloned before modification and column
attributes like checkbox renderers are preserved for variant-highlighted
cells.

Fixes https://gitlab.com/kicad/code/kicad/-/issues/22856

eeschema/fields_data_model.cpp

@@ -362,18 +362,19 @@ wxString FIELDS_EDITOR_GRID_DATA_MODEL::GetValue( int aRow, int aCol )
 wxGridCellAttr* FIELDS_EDITOR_GRID_DATA_MODEL::GetAttr( int aRow, int aCol, wxGridCellAttr::wxAttrKind aKind )
 {
     wxGridCellAttr* attr = nullptr;
+    bool            needsUrlEditor = false;
+    bool            needsVariantHighlight = false;
+    wxColour        highlightColor;
 
+    // Check if we need URL editor
     if( GetColFieldName( aCol ) == GetCanonicalFieldName( FIELD_T::DATASHEET )
             || IsURL( GetValue( m_rows[aRow], aCol ) ) )
     {
         if( m_urlEditor )
-        {
-            m_urlEditor->IncRef();
-            attr = m_urlEditor;
-        }
+            needsUrlEditor = true;
     }
 
-    // Highlight cells that differ from default when viewing a variant
+    // Check if we need variant highlighting
     if( !m_currentVariant.IsEmpty() && aRow >= 0 && aRow < (int) m_rows.size()
             && aCol >= 0 && aCol < (int) m_cols.size() )
     {
@@ -385,8 +386,6 @@ wxGridCellAttr* FIELDS_EDITOR_GRID_DATA_MODEL::GetAttr( int aRow, int aCol, wxGr
             const DATA_MODEL_ROW& row = m_rows[aRow];
 
             // Check if any symbol in this row has a variant-specific value
-            bool hasVariantDifference = false;
-
             for( const SCH_REFERENCE& ref : row.m_Refs )
             {
                 wxString defaultValue = getDefaultFieldValue( ref, fieldName );
@@ -407,54 +406,60 @@ wxGridCellAttr* FIELDS_EDITOR_GRID_DATA_MODEL::GetAttr( int aRow, int aCol, wxGr
 
                 if( currentValue != defaultValue )
                 {
-                    hasVariantDifference = true;
+                    needsVariantHighlight = true;
+
+                    // Use a subtle highlight color that works in both light and dark themes
+                    wxColour bg = wxSystemSettings::GetColour( wxSYS_COLOUR_WINDOW );
+                    bool     isDark = ( bg.Red() + bg.Green() + bg.Blue() ) < 384;
+
+                    if( isDark )
+                        highlightColor = wxColour( 80, 80, 40 );   // Dark gold/brown
+                    else
+                        highlightColor = wxColour( 255, 255, 200 ); // Light yellow
+
                     break;
                 }
             }
-
-            if( hasVariantDifference )
-            {
-                if( !attr )
-                {
-                    attr = new wxGridCellAttr();
-                }
-                else
-                {
-                    // Clone so we don't modify the shared URL editor attr
-                    wxGridCellAttr* newAttr = attr->Clone();
-                    attr->DecRef();
-                    attr = newAttr;
-                }
-
-                // Use a subtle highlight color that works in both light and dark themes
-                // Light yellow in light mode, darker yellow-ish in dark mode
-                wxColour bg = wxSystemSettings::GetColour( wxSYS_COLOUR_WINDOW );
-                bool isDark = ( bg.Red() + bg.Green() + bg.Blue() ) < 384;
-
-                if( isDark )
-                    attr->SetBackgroundColour( wxColour( 80, 80, 40 ) );  // Dark gold/brown
-                else
-                    attr->SetBackgroundColour( wxColour( 255, 255, 200 ) );  // Light yellow
-            }
         }
     }
 
-    // Merge with column attributes (renderer, editor, alignment, etc.) set by SetColAttr().
-    // This ensures checkbox renderers and other column-specific attributes are preserved
-    // when we've created a custom attr for highlighting or URL editing.
-    if( attr )
-    {
-        wxGridCellAttr* colAttr = m_colAttrs.count( aCol ) ? m_colAttrs[aCol] : nullptr;
+    // If we don't need any custom attributes, use the base class behavior
+    if( !needsUrlEditor && !needsVariantHighlight )
+        return WX_GRID_TABLE_BASE::GetAttr( aRow, aCol, aKind );
 
-        if( colAttr )
+    // URL cells: use m_urlEditor as base, potentially with variant highlight overlay
+    if( needsUrlEditor )
+    {
+        if( needsVariantHighlight )
         {
-            attr->MergeWith( colAttr );
+            // Clone the URL editor attribute and add highlight color
+            attr = m_urlEditor->Clone();
+            attr->SetBackgroundColour( highlightColor );
+        }
+        else
+        {
+            // Just use the URL editor attribute directly
+            m_urlEditor->IncRef();
+            attr = m_urlEditor;
         }
 
         return enhanceAttr( attr, aRow, aCol, aKind );
     }
 
-    return WX_GRID_TABLE_BASE::GetAttr( aRow, aCol, aKind );
+    // Non-URL cells with variant highlighting: start with column attributes if they exist.
+    // This preserves checkbox renderers and other column-specific settings.
+    if( m_colAttrs.find( aCol ) != m_colAttrs.end() && m_colAttrs[aCol] )
+    {
+        attr = m_colAttrs[aCol]->Clone();
+    }
+    else
+    {
+        attr = new wxGridCellAttr();
+    }
+
+    attr->SetBackgroundColour( highlightColor );
+
+    return enhanceAttr( attr, aRow, aCol, aKind );
 }