From da28a6e4185f201c6f0fd44dfd2b55e574a34839 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 15 Dec 2023 19:15:56 +0100
Subject: [PATCH] Don't share style instances with Or selector. (#13969)

* Added failing test for #13910.

* Don't share style instances with Or selector.

Fixes #13910.
---
 src/Avalonia.Base/Styling/ControlTheme.cs     |  2 +-
 src/Avalonia.Base/Styling/Style.cs            |  2 +-
 src/Avalonia.Base/Styling/StyleBase.cs        | 10 +++--
 .../Styling/StyleTests.cs                     | 39 +++++++++++++++++++
 4 files changed, 48 insertions(+), 5 deletions(-)

diff --git a/src/Avalonia.Base/Styling/ControlTheme.cs b/src/Avalonia.Base/Styling/ControlTheme.cs
index 75a3beb907..6cd09e1808 100644
--- a/src/Avalonia.Base/Styling/ControlTheme.cs
+++ b/src/Avalonia.Base/Styling/ControlTheme.cs
@@ -48,7 +48,7 @@ namespace Avalonia.Styling
 
             if (HasSettersOrAnimations && TargetType.IsAssignableFrom(StyledElement.GetStyleKey(target)))
             {
-                Attach(target, null, type);
+                Attach(target, null, type, true);
                 return SelectorMatchResult.AlwaysThisType;
             }
 
diff --git a/src/Avalonia.Base/Styling/Style.cs b/src/Avalonia.Base/Styling/Style.cs
index a5d89392e9..44ffc22e91 100644
--- a/src/Avalonia.Base/Styling/Style.cs
+++ b/src/Avalonia.Base/Styling/Style.cs
@@ -74,7 +74,7 @@ namespace Avalonia.Styling
 
                 if (match.IsMatch)
                 {
-                    Attach(target, match.Activator, type);
+                    Attach(target, match.Activator, type, Selector is not OrSelector);
                 }
 
                 result = match.Result;
diff --git a/src/Avalonia.Base/Styling/StyleBase.cs b/src/Avalonia.Base/Styling/StyleBase.cs
index 318e8d6890..bc3457cb48 100644
--- a/src/Avalonia.Base/Styling/StyleBase.cs
+++ b/src/Avalonia.Base/Styling/StyleBase.cs
@@ -92,20 +92,24 @@ namespace Avalonia.Styling
             return false;
         }
 
-        internal ValueFrame Attach(StyledElement target, IStyleActivator? activator, FrameType type)
+        internal ValueFrame Attach(
+            StyledElement target,
+            IStyleActivator? activator,
+            FrameType type,
+            bool canShareInstance)
         {
             if (target is not AvaloniaObject ao)
                 throw new InvalidOperationException("Styles can only be applied to AvaloniaObjects.");
 
             StyleInstance instance;
 
-            if (_sharedInstance is not null)
+            if (_sharedInstance is not null && canShareInstance)
             {
                 instance = _sharedInstance;
             }
             else
             {
-                var canShareInstance = activator is null;
+                canShareInstance &= activator is null;
 
                 instance = new StyleInstance(this, activator, type);
 
diff --git a/tests/Avalonia.Base.UnitTests/Styling/StyleTests.cs b/tests/Avalonia.Base.UnitTests/Styling/StyleTests.cs
index 52bee42d9d..b44078caeb 100644
--- a/tests/Avalonia.Base.UnitTests/Styling/StyleTests.cs
+++ b/tests/Avalonia.Base.UnitTests/Styling/StyleTests.cs
@@ -1029,6 +1029,28 @@ namespace Avalonia.Base.UnitTests.Styling
             Assert.Equal(Brushes.Blue, border.Background);
         }
 
+        [Fact]
+        public void Should_Not_Share_Instance_When_Or_Selector_Is_Present()
+        {
+            // Issue #13910
+            Style style = new Style(x => Selectors.Or(x.OfType<Class1>(), x.OfType<Class2>().Class("bar")))
+            {
+                Setters =
+                {
+                    new Setter(Class1.FooProperty, "Foo"),
+                },
+            };
+
+            var target1 = new Class1 { Classes = { "foo" } };
+            var target2 = new Class2();
+
+            StyleHelpers.TryAttach(style, target1);
+            StyleHelpers.TryAttach(style, target2);
+
+            Assert.Equal("Foo", target1.Foo);
+            Assert.Equal("foodefault", target2.Foo);
+        }
+
         private class Class1 : Control
         {
             public static readonly StyledProperty<string> FooProperty =
@@ -1063,5 +1085,22 @@ namespace Avalonia.Base.UnitTests.Styling
                 throw new NotImplementedException();
             }
         }
+
+        private class Class2 : Control
+        {
+            public static readonly StyledProperty<string> FooProperty =
+                Class1.FooProperty.AddOwner<Class2>();
+
+            public string Foo
+            {
+                get { return GetValue(FooProperty); }
+                set { SetValue(FooProperty, value); }
+            }
+
+            protected override void OnPropertyChanged(AvaloniaPropertyChangedEventArgs change)
+            {
+                base.OnPropertyChanged(change);
+            }
+        }
     }
 }