Log warnings for converter exceptions.

src/Avalonia.Base/Data/Core/BindingExpression.cs

@@ -8,6 +8,7 @@ using Avalonia.Data.Converters;
 using Avalonia.Data.Core.ExpressionNodes;
 using Avalonia.Data.Core.Parsers;
 using Avalonia.Logging;
+using static Avalonia.Rendering.Composition.Animations.PropertySetSnapshot;
 
 namespace Avalonia.Data.Core;
 
@@ -540,7 +541,7 @@ internal class BindingExpression : IObservable<object?>,
         }
     }
 
-    private static object? Convert(
+    private object? Convert(
         IValueConverter converter,
         object? converterParameter,
         object? value,
@@ -554,8 +555,12 @@ internal class BindingExpression : IObservable<object?>,
         {
             var valueString = value?.ToString() ?? "(null)";
             var valueTypeName = value?.GetType().FullName ?? "null";
-            var ex = new InvalidCastException(
-                $"Could not convert '{valueString}' ({valueTypeName}) to {targetType} using '{converter}'.", e);
+            var message = $"Could not convert '{valueString}' ({valueTypeName}) to '{targetType}' using '{converter}'";
+
+            if (ShouldLogError(out var target))
+                Log(target, $"{message}: {e.Message}", LogEventLevel.Warning);
+
+            var ex = new InvalidCastException(message + '.', e);
             return new BindingNotification(ex, BindingErrorType.Error);
         }
     }

tests/Avalonia.Markup.UnitTests/Data/BindingTests_Logging.cs

@@ -1,7 +1,10 @@
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using Avalonia.Controls;
+using Avalonia.Controls.Converters;
 using Avalonia.Data;
+using Avalonia.Data.Converters;
 using Avalonia.Data.Core;
 using Avalonia.Data.Core.Plugins.Reflection;
 using Avalonia.Input;
@@ -248,6 +251,28 @@ namespace Avalonia.Markup.UnitTests.Data
                     target.Bind(Control.MarginProperty, binding);
                 }
             }
+
+            [Fact]
+            public void Should_Log_Error_For_Unconvertible_Type_With_Converter()
+            {
+                var target = new Decorator { DataContext = new { Foo = new System.Version() } };
+                var root = new TestRoot(target);
+                var binding = new Binding("Foo")
+                {
+                    Converter = new ThrowingConverter(),
+                };
+
+                using (AssertLog(
+                    target,
+                    binding.Path,
+                    "Could not convert '0.0' (System.Version) to 'Avalonia.Thickness' " +
+                    "using 'Avalonia.Markup.UnitTests.Data.BindingTests_Logging+ThrowingConverter': " +
+                    "The method or operation is not implemented.",
+                    property: Control.MarginProperty))
+                {
+                    target.Bind(Control.MarginProperty, binding);
+                }
+            }
         }
 
         public class Fallback
@@ -447,6 +472,19 @@ namespace Avalonia.Markup.UnitTests.Data
             public string? Foo { get; set; }
         }
 
+        private class ThrowingConverter : IValueConverter
+        {
+            public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
+            {
+                throw new NotImplementedException();
+            }
+
+            public object? ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)
+            {
+                throw new NotImplementedException();
+            }
+        }
+
         private record LogMessage(LogEventLevel level, string area, object source, string messageTemplate, params object[] propertyValues);
     }
 }