Add IsAzureArm to distinguish MPG and DPG (#47374)

eng/Packages.Data.props

@@ -254,7 +254,7 @@
   </ItemGroup>
 
   <ItemGroup Condition="'$(IsGeneratorLibrary)' == 'true'">
-    <PackageReference Update="Microsoft.Generator.CSharp.ClientModel" Version="1.0.0-alpha.20241121.2" />
+    <PackageReference Update="Microsoft.Generator.CSharp.ClientModel" Version="1.0.0-alpha.20241128.1" />
   </ItemGroup>
 
   <!--

eng/packages/http-client-csharp/emitter/src/emitter.ts

@@ -5,11 +5,14 @@ import { EmitContext } from "@typespec/compiler";
 
 import {
   $onEmit as $OnMGCEmit,
-  NetEmitterOptions
+  NetEmitterOptions,
+  setSDKContextOptions
 } from "@typespec/http-client-csharp";
+import { azureSDKContextOptions } from "./sdk-context-options.js";
 
 export async function $onEmit(context: EmitContext<NetEmitterOptions>) {
   context.options["plugin-name"] = "AzureClientPlugin";
   context.options["emitter-extension-path"] = import.meta.url;
+  setSDKContextOptions(azureSDKContextOptions);
   await $OnMGCEmit(context);
 }

eng/packages/http-client-csharp/emitter/src/sdk-context-options.ts

@@ -0,0 +1,14 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License. See License.txt in the project root for license information.
+
+import { CreateSdkContextOptions } from "@azure-tools/typespec-client-generator-core";
+
+export const azureSDKContextOptions: CreateSdkContextOptions = {
+    versioning: {},
+    additionalDecorators: [
+        // https://github.com/Azure/typespec-azure/blob/main/packages/typespec-client-generator-core/README.md#usesystemtextjsonconverter
+        "Azure\\.ClientGenerator\\.Core\\.@useSystemTextJsonConverter",
+        // https://github.com/Azure/typespec-azure/blob/main/packages/typespec-azure-resource-manager/README.md#armprovidernamespace
+        "Azure\\.ResourceManager\\.@armProviderNamespace"
+    ]
+};

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

@@ -4,9 +4,11 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.Generator.CSharp;
 using Microsoft.Generator.CSharp.ClientModel;
+using Microsoft.Generator.CSharp.Input;
 using System;
 using System.ComponentModel.Composition;
 using System.IO;
+using System.Linq;
 
 namespace Azure.Generator;
 
@@ -56,4 +58,9 @@ public override void Configure()
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 """;
+
+    /// <summary>
+    /// Identify if the input is generated for Azure ARM.
+    /// </summary>
+    internal Lazy<bool> IsAzureArm => new Lazy<bool>(() => InputLibrary.InputNamespace.Clients.Any(c => c.Decorators.Any(d => d.Name.Equals("Azure.ResourceManager.@armProviderNamespace"))));
 }