feat: Enable Rule CA2211

.editorconfig

@@ -169,6 +169,8 @@ dotnet_diagnostic.CA1828.severity = warning
 dotnet_diagnostic.CA1829.severity = warning
 #CA1847: Use string.Contains(char) instead of string.Contains(string) with single characters
 dotnet_diagnostic.CA1847.severity = warning
+#CACA2211:Non-constant fields should not be visible
+dotnet_diagnostic.CA2211.severity = error
 
 # Wrapping preferences
 csharp_wrap_before_ternary_opsigns = false

src/Avalonia.Controls.ColorPicker/ColorPalettes/FlatColorPalette.cs

@@ -289,8 +289,8 @@ public enum FlatColor : uint
         };
 
         // See: https://htmlcolorcodes.com/assets/downloads/flat-design-colors/flat-design-color-chart.png
-        protected static Color[,]? _colorChart = null;
-        protected static object _colorChartMutex = new object();
+        private static Color[,]? _colorChart = null;
+        private static readonly object _colorChartMutex = new();
 
         /// <summary>
         /// Initializes all color chart colors.

src/Avalonia.Controls.ColorPicker/ColorPalettes/FlatHalfColorPalette.cs

@@ -10,8 +10,8 @@ namespace Avalonia.Controls
     /// <inheritdoc cref="FlatColorPalette"/>
     public class FlatHalfColorPalette : IColorPalette
     {
-        protected static Color[,]? _colorChart = null;
-        protected static object _colorChartMutex = new object();
+        private static Color[,]? _colorChart = null;
+        private static readonly object _colorChartMutex = new();
 
         /// <summary>
         /// Initializes all color chart colors.

src/Avalonia.Controls.ColorPicker/ColorPalettes/MaterialColorPalette.cs

@@ -344,8 +344,8 @@ public enum MaterialColor : uint
 
         // See: https://material.io/design/color/the-color-system.html#tools-for-picking-colors
         // This is a reduced palette for uniformity
-        protected static Color[,]? _colorChart = null;
-        protected static object _colorChartMutex = new object();
+        private static Color[,]? _colorChart = null;
+        private static readonly object _colorChartMutex = new();
 
         /// <summary>
         /// Initializes all color chart colors.

src/Avalonia.Controls.ColorPicker/ColorPalettes/MaterialHalfColorPalette.cs

@@ -10,8 +10,8 @@ namespace Avalonia.Controls
     /// <inheritdoc cref="MaterialColorPalette"/>
     public class MaterialHalfColorPalette : IColorPalette
     {
-        protected static Color[,]? _colorChart = null;
-        protected static object _colorChartMutex = new object();
+        private static Color[,]? _colorChart = null;
+        private static readonly object _colorChartMutex = new();
 
         /// <summary>
         /// Initializes all color chart colors.

src/Avalonia.Controls.DataGrid/DataGridCheckBoxColumn.cs

@@ -31,7 +31,7 @@ public DataGridCheckBoxColumn()
         /// <summary>
         /// Defines the <see cref="IsThreeState"/> property.
         /// </summary>
-        public static StyledProperty<bool> IsThreeStateProperty =
+        public static readonly StyledProperty<bool> IsThreeStateProperty =
             CheckBox.IsThreeStateProperty.AddOwner<DataGridCheckBoxColumn>();
 
         /// <summary>

src/Avalonia.Controls.DataGrid/DataGridColumn.cs

@@ -185,7 +185,7 @@ internal ICellEditBinding CellEditBinding
         /// <summary>
         /// Defines the <see cref="IsVisible"/> property.
         /// </summary>
-        public static StyledProperty<bool> IsVisibleProperty =
+        public static readonly StyledProperty<bool> IsVisibleProperty =
              Control.IsVisibleProperty.AddOwner<DataGridColumn>();
 
         /// <summary>

src/Avalonia.Controls/Diagnostics/ToolTipDiagnostics.cs

@@ -8,6 +8,6 @@ public static class ToolTipDiagnostics
         /// <summary>
         /// Provides access to the internal <see cref="ToolTip.ToolTipProperty"/> for use in DevTools.
         /// </summary>
-        public static AvaloniaProperty<ToolTip?> ToolTipProperty = ToolTip.ToolTipProperty;
+        public static readonly AvaloniaProperty<ToolTip?> ToolTipProperty = ToolTip.ToolTipProperty;
     }
 }