Fix #1717

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/BindingExtension.cs

@@ -88,18 +88,26 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             {
                 result.Path = string.Empty;
             }
-            else if (path.StartsWith("#"))
+            else if (path.StartsWith("!"))
+            {
+                int pathStart = 0;
+                for (; pathStart < path.Length && path[pathStart] == '!'; ++pathStart);
+                result.Path = path.Substring(0, pathStart);
+                path = path.Substring(pathStart);
+            }
+
+            if (path.StartsWith("#"))
             {
                 var dot = path.IndexOf('.');
 
                 if (dot != -1)
                 {
-                    result.Path = path.Substring(dot + 1);
+                    result.Path += path.Substring(dot + 1);
                     result.ElementName = path.Substring(1, dot - 1);
                 }
                 else
                 {
-                    result.Path = string.Empty;
+                    result.Path += string.Empty;
                     result.ElementName = path.Substring(1);
                 }
             }
@@ -114,12 +122,12 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
                 string relativeSourceMode;
                 if (dot != -1)
                 {
-                    result.Path = path.Substring(dot + 1);
+                    result.Path += path.Substring(dot + 1);
                     relativeSourceMode = path.Substring(1, dot - 1);
                 }
                 else
                 {
-                    result.Path = string.Empty;
+                    result.Path += string.Empty;
                     relativeSourceMode = path.Substring(1);
                 }
 
@@ -170,7 +178,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             }
             else
             {
-                result.Path = path;
+                result.Path += path;
             }
 
             return result;
@@ -229,4 +237,4 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
 
         public RelativeSource RelativeSource { get; set; }
     }
-}
+}

tests/Avalonia.Markup.Xaml.UnitTests/Xaml/BindingTests_RelativeSource.cs

@@ -297,7 +297,60 @@ namespace Avalonia.Markup.Xaml.UnitTests.Xaml
                 Assert.Equal("title", button.Content);
             }
         }
+
+        [Fact]
+        public void Shorthand_Binding_With_Negation_Works()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml;assembly=Avalonia.Markup.Xaml.UnitTests'>
+    <Border Name='border1'>
+      <Border Name='border2'>
+        <Button Name='button' Content='{Binding !$self.IsDefault}'/>
+      </Border>
+    </Border>
+</Window>";
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var button = window.FindControl<Button>("button");
+
+                window.ApplyTemplate();
+
+#pragma warning disable xUnit2004 // Diagnostic mis-firing since button.Content isn't guaranteed to be a bool.
+                Assert.Equal(true, button.Content);
+#pragma warning restore xUnit2004
+            }
+        }
+        [Fact]
+        public void Shorthand_Binding_With_Multiple_Negation_Works()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var xaml = @"
+<Window xmlns='https://github.com/avaloniaui'
+        xmlns:x='http://schemas.microsoft.com/winfx/2006/xaml'
+        xmlns:local='clr-namespace:Avalonia.Markup.Xaml.UnitTests.Xaml;assembly=Avalonia.Markup.Xaml.UnitTests'>
+    <Border Name='border1'>
+      <Border Name='border2'>
+        <Button Name='button' Content='{Binding !!$self.IsDefault}'/>
+      </Border>
+    </Border>
+</Window>";
+                var loader = new AvaloniaXamlLoader();
+                var window = (Window)loader.Load(xaml);
+                var button = window.FindControl<Button>("button");
+
+                window.ApplyTemplate();
+
+#pragma warning disable xUnit2004 // Diagnostic mis-firing since button.Content isn't guaranteed to be a bool.
+                Assert.Equal(false, button.Content);
+#pragma warning restore xUnit2004
+            }
+        }
     }
 
     public class TestWindow : Window { }
-}
+}