From c81e5007d7923be988d46ed829180231490f462e Mon Sep 17 00:00:00 2001
From: Tom McDonald <tommcdon@microsoft.com>
Date: Thu, 20 Aug 2026 09:29:29 -0400
Subject: [PATCH] Fix CCW discovery for bindable property types

Ensure property values exposed through GeneratedBindableCustomProperty contribute their concrete types to the generated CCW lookup table.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 .../WinRT.SourceGenerator/AotOptimizer.cs     | 14 +++--
 .../SourceGeneratorTest/AotOptimizerTests.cs  | 53 +++++++++++++++++++
 2 files changed, 64 insertions(+), 3 deletions(-)

diff --git a/src/Authoring/WinRT.SourceGenerator/AotOptimizer.cs b/src/Authoring/WinRT.SourceGenerator/AotOptimizer.cs
index 07b4aa662..55551c4a1 100644
--- a/src/Authoring/WinRT.SourceGenerator/AotOptimizer.cs
+++ b/src/Authoring/WinRT.SourceGenerator/AotOptimizer.cs
@@ -1319,13 +1319,17 @@ private static EquatableArray<VtableAttribute> GetVtableAttributesToAddOnLookupT
             }
             else if (context.Node is PropertyDeclarationSyntax propertyDeclaration)
             {
+                var isGeneratedBindableCustomPropertyClass =
+                    context.SemanticModel.GetDeclaredSymbol(propertyDeclaration) is IPropertySymbol propertySymbol &&
+                    GeneratorHelper.IsGeneratedBindableCustomPropertyClass(context.SemanticModel.Compilation, propertySymbol.ContainingSymbol);
+
                 // Detect scenarios where the property declaration has an initializer and is to a boxed or cast type during initialization.
                 if (propertyDeclaration.Initializer != null)
                 {
                     var leftSymbol = context.SemanticModel.GetSymbolInfo(propertyDeclaration.Type).Symbol;
                     if (leftSymbol is INamedTypeSymbol namedType)
                     {
-                        AddVtableAttributesForExpression(propertyDeclaration.Initializer.Value, namedType);
+                        AddVtableAttributesForExpression(propertyDeclaration.Initializer.Value, namedType, isGeneratedBindableCustomPropertyClass);
                     }
                 }
                 else if (propertyDeclaration.ExpressionBody != null)
@@ -1333,7 +1337,7 @@ private static EquatableArray<VtableAttribute> GetVtableAttributesToAddOnLookupT
                     var leftSymbol = context.SemanticModel.GetSymbolInfo(propertyDeclaration.Type).Symbol;
                     if (leftSymbol is INamedTypeSymbol namedType)
                     {
-                        AddVtableAttributesForExpression(propertyDeclaration.ExpressionBody.Expression, namedType);
+                        AddVtableAttributesForExpression(propertyDeclaration.ExpressionBody.Expression, namedType, isGeneratedBindableCustomPropertyClass);
                     }
                 }
             }
@@ -1355,7 +1359,11 @@ private static EquatableArray<VtableAttribute> GetVtableAttributesToAddOnLookupT
                     var propertyTypeSymbol = context.SemanticModel.GetSymbolInfo(propertyDeclarationSyntax.Type).Symbol;
                     if (propertyTypeSymbol is ITypeSymbol typeSymbol)
                     {
-                        AddVtableAttributesForExpression(returnDeclaration.Expression, typeSymbol);
+                        var isGeneratedBindableCustomPropertyClass =
+                            context.SemanticModel.GetDeclaredSymbol(propertyDeclarationSyntax) is IPropertySymbol propertySymbol &&
+                            GeneratorHelper.IsGeneratedBindableCustomPropertyClass(context.SemanticModel.Compilation, propertySymbol.ContainingSymbol);
+
+                        AddVtableAttributesForExpression(returnDeclaration.Expression, typeSymbol, isGeneratedBindableCustomPropertyClass);
                     }
                 }
             }
diff --git a/src/Tests/SourceGeneratorTest/AotOptimizerTests.cs b/src/Tests/SourceGeneratorTest/AotOptimizerTests.cs
index 58c162c7c..ec8c6eea7 100644
--- a/src/Tests/SourceGeneratorTest/AotOptimizerTests.cs
+++ b/src/Tests/SourceGeneratorTest/AotOptimizerTests.cs
@@ -121,6 +121,59 @@ public List<int> M()
         Assert.IsFalse(generated.Contains("System.Collections.Generic.List`1[System.Int32]"));
     }
 
+    [TestMethod]
+    public void GeneratedBindableCustomProperty_DiscoversPropertyTypes()
+    {
+        const string source = """
+            using System.Collections.ObjectModel;
+            using WinRT;
+
+            [GeneratedBindableCustomProperty]
+            internal partial class ViewModel
+            {
+                private readonly ObservableCollection<string> items = new();
+
+                public ObservableCollection<string> Items
+                {
+                    get { return items; }
+                }
+
+                public ObservableCollection<int> Numbers { get; } = new();
+
+                public ObservableCollection<double> Values => new();
+            }
+            """;
+
+        string generated = RunAotOptimizer(source);
+
+        Assert.IsTrue(generated.Contains("System.Collections.ObjectModel.ObservableCollection`1[System.String]"));
+        Assert.IsTrue(generated.Contains("System.Collections.ObjectModel.ObservableCollection`1[System.Int32]"));
+        Assert.IsTrue(generated.Contains("System.Collections.ObjectModel.ObservableCollection`1[System.Double]"));
+        Assert.IsTrue(generated.Contains("Windows.Foundation.Collections.IVector`1<String>"));
+    }
+
+    [TestMethod]
+    public void NonBindableProperties_DoNotDiscoverConcreteTypes()
+    {
+        const string source = """
+            using System.Collections.ObjectModel;
+
+            internal class ViewModel
+            {
+                private readonly ObservableCollection<string> items = new();
+
+                public ObservableCollection<string> Items
+                {
+                    get { return items; }
+                }
+            }
+            """;
+
+        string generated = RunAotOptimizer(source);
+
+        Assert.IsFalse(generated.Contains("System.Collections.ObjectModel.ObservableCollection`1[System.String]"));
+    }
+
     private static string RunAotOptimizer(string source)
     {
         SyntaxTree syntaxTree = CSharpSyntaxTree.ParseText(source, new CSharpParseOptions(LanguageVersion.Latest));