Make pipeline property virtual (Azure#49920)

* Make pipeline property virtual

* regen

Author: JoshLove-msft

eng/Packages.Data.props

@@ -206,8 +206,8 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(IsGeneratorLibrary)' == 'true'">
-    <PackageReference Update="Microsoft.TypeSpec.Generator.ClientModel" Version="1.0.0-alpha.20250507.1" />
-    <PackageReference Update="Microsoft.TypeSpec.Generator.Input" Version="1.0.0-alpha.20250507.1" />
+    <PackageReference Update="Microsoft.TypeSpec.Generator.ClientModel" Version="1.0.0-alpha.20250508.3" />
+    <PackageReference Update="Microsoft.TypeSpec.Generator.Input" Version="1.0.0-alpha.20250508.3" />
     <PackageReference Update="Azure.Generator" Version="1.0.0-alpha.20250429.2" />
     <PackageReference Update="System.ClientModel" Version="1.4.0" />
   </ItemGroup>

eng/packages/http-client-csharp/generator/Azure.Generator/src/AzureClientGenerator.cs

@@ -51,5 +51,6 @@ protected override void Configure()
         AddSharedSourceDirectory(sharedSourceDirectory);
         AddVisitor(new NamespaceVisitor());
         AddVisitor(new DistributedTracingVisitor());
+        AddVisitor(new PipelinePropertyVisitor());
     }
 }

eng/packages/http-client-csharp/generator/Azure.Generator/src/Visitors/PipelinePropertyVisitor.cs

@@ -0,0 +1,28 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using Azure.Core.Pipeline;
+using Microsoft.TypeSpec.Generator.ClientModel;
+using Microsoft.TypeSpec.Generator.Primitives;
+using Microsoft.TypeSpec.Generator.Providers;
+
+namespace Azure.Generator.Visitors
+{
+    /// <summary>
+    /// Makes the Pipeline property virtual for consistency and backwards compatibility with existing
+    /// Azure libraries.
+    /// </summary>
+    internal class PipelinePropertyVisitor : ScmLibraryVisitor
+    {
+        protected override PropertyProvider? VisitProperty(PropertyProvider property)
+        {
+            if (property.Type.Equals(typeof(HttpPipeline)))
+            {
+                // Add the virtual modifier for the HttpPipeline property for backwards compatibility.
+                property.Update(modifiers: property.Modifiers | MethodSignatureModifiers.Virtual);
+            }
+
+            return property;
+        }
+    }
+}