Make bindings react to PropertyChanged even if property hasn't changed (#16150)

* Added failing test for #16137.

* Raise node change even if value hasn't changed.

Fixes #16137.

src/Avalonia.Base/Data/Core/ExpressionNodes/ExpressionNode.cs

@@ -211,24 +211,8 @@ internal abstract class ExpressionNode
     protected void SetValue(object? value, Exception? dataValidationError = null)
     {
         Debug.Assert(value is not BindingNotification);
-
-        if (Owner is null)
-            return;
-
-        // We raise a change notification if:
-        //
-        // - This is the initial value (_value is null)
-        // - There is a data validation error
-        // - There is no data validation error, but the owner has one
-        // - The new value is different to the old value
-        if (_value is null ||
-            dataValidationError is not null ||
-            (dataValidationError is null && Owner.ErrorType == BindingErrorType.DataValidationError) ||
-            !Equals(value, _value))
-        {
-            _value = value;
-            Owner.OnNodeValueChanged(Index, value, dataValidationError);
-        }
+        _value = value;
+        Owner?.OnNodeValueChanged(Index, value, dataValidationError);
     }
 
     /// <summary>

tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.Property.cs

@@ -226,6 +226,26 @@ namespace Avalonia.Base.UnitTests.Data.Core
             GC.KeepAlive(data);
         }
 
+        [Fact]
+        public void Converter_Should_Be_Called_On_PropertyChanged_Even_If_Property_Not_Changed()
+        {
+            // Issue #16137
+            var data = new ViewModel();
+            var converter = new PrefixConverter("foo");
+            var target = CreateTargetWithSource(
+                data,
+                o => o.IntValue,
+                converter: converter,
+                targetProperty: TargetClass.StringProperty);
+
+            Assert.Equal("foo0", target.String);
+
+            converter.Prefix = "bar";
+            data.RaisePropertyChanged(nameof(data.IntValue));
+
+            Assert.Equal("bar0", target.String);
+        }
+
         private class DerivedViewModel : ViewModel
         {
         }

tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.cs

@@ -417,14 +417,20 @@ public abstract partial class BindingExpressionTests
 
     protected class PrefixConverter : IValueConverter
     {
+        public PrefixConverter(string? prefix = null) => Prefix = prefix;
+
+        public string? Prefix { get; set; }
+
         public object? Convert(object? value, Type targetType, object? parameter, CultureInfo culture)
         {
             if (targetType != typeof(string))
                 return value;
 
             var result = value?.ToString() ?? string.Empty;
-            if (parameter is not null)
-                result = parameter.ToString() + result;
+            var prefix = parameter?.ToString() ?? Prefix;
+
+            if (prefix is not null)
+                result = prefix + result;
             return result;
         }