From 2f0e075d96d1b8a4ad4042c1a28014bd8cbaa0cd Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@users.noreply.github.com>
Date: Fri, 20 Oct 2023 17:37:56 +0200
Subject: [PATCH] Don't log errors for named control bindings...

...on elements which aren't yet rooted.
---
 .../Core/ExpressionNodes/NamedElementNode.cs  | 11 ++++-
 .../Data/BindingTests_Logging.cs              | 47 +++++++++++++++++++
 2 files changed, 57 insertions(+), 1 deletion(-)

diff --git a/src/Avalonia.Base/Data/Core/ExpressionNodes/NamedElementNode.cs b/src/Avalonia.Base/Data/Core/ExpressionNodes/NamedElementNode.cs
index daf1b21506..71066d5888 100644
--- a/src/Avalonia.Base/Data/Core/ExpressionNodes/NamedElementNode.cs
+++ b/src/Avalonia.Base/Data/Core/ExpressionNodes/NamedElementNode.cs
@@ -1,11 +1,12 @@
 using System;
 using System.Text;
 using Avalonia.Controls;
+using Avalonia.LogicalTree;
 using Avalonia.Reactive;
 
 namespace Avalonia.Data.Core.ExpressionNodes;
 
-internal class NamedElementNode : ExpressionNode
+internal class NamedElementNode : SourceNode
 {
     private readonly WeakReference<INameScope?> _nameScope;
     private readonly string _name;
@@ -23,10 +24,18 @@ internal class NamedElementNode : ExpressionNode
         builder.Append(_name);
     }
 
+    public override bool ShouldLogErrors(object target)
+    {
+        // We don't log errors when the target element isn't rooted.
+        return target is not ILogical logical || logical.IsAttachedToLogicalTree;
+    }
+
     protected override void OnSourceChanged(object source)
     {
         if (_nameScope.TryGetTarget(out var scope))
             _subscription = NameScopeLocator.Track(scope, _name).Subscribe(SetValue);
+        else
+            SetError("NameScope not found.");
     }
 
     protected override void Unsubscribe(object oldSource)
diff --git a/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Logging.cs b/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Logging.cs
index 5792b98653..4d215ccc3b 100644
--- a/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Logging.cs
+++ b/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Logging.cs
@@ -6,6 +6,7 @@ using Avalonia.Data.Core;
 using Avalonia.Data.Core.Plugins.Reflection;
 using Avalonia.Input;
 using Avalonia.Logging;
+using Avalonia.LogicalTree;
 using Avalonia.Markup.Xaml.MarkupExtensions;
 using Avalonia.Markup.Xaml.MarkupExtensions.CompiledBindings;
 using Avalonia.Reactive;
@@ -120,6 +121,52 @@ namespace Avalonia.Markup.UnitTests.Data
             }
         }
 
+        public class NamedElement
+        {
+            [Fact]
+            public void Should_Log_NameScope_Not_Found()
+            {
+                var target = new Decorator { };
+                var root = new TestRoot(target);
+                var binding = new Binding("#source") { TypeResolver = ResolveType };
+
+                using (AssertLog(target, binding.Path, "NameScope not found.", "#source"))
+                {
+                    target.Bind(Control.TagProperty, binding);
+                }
+            }
+
+            [Fact]
+            public void Should_Not_Log_Element_Property_Null_For_Unrooted_Control()
+            {
+                var ns = new NameScope();
+                var source = new Canvas { Name = "source" };
+                var target = new Decorator { };
+                var binding = new Binding("#source.DataContext.Foo") { TypeResolver = ResolveType, NameScope = new(ns) };
+                var container = new StackPanel 
+                { 
+                    [NameScope.NameScopeProperty] = ns,
+                    Children = { source, target }
+                };
+
+                ns.Register(source.Name, source);
+
+                using (AssertNoLog())
+                {
+                    target.Bind(Control.TagProperty, binding);
+                }
+
+                // Sanity check to that the binding works when rooted: make sure that we're not just testing a broken
+                // binding!
+                using (AssertNoLog())
+                {
+                    var root = new TestRoot(container);
+                    root.DataContext = new { Foo = "foo" };
+                    Assert.Equal("foo", target.Tag);
+                }
+            }
+        }
+
         public class VisualAncestor
         {
             [Fact]