fix the default API version in rest client issue. (Azure#51827)

* fix the default api version in rest client issue.

* fix unit tests.

* remove debug code commited by accident.

* address review comments.

* refine.

* fix ut.

Author: haiyuazhang

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/src/ManagementInputLibrary.cs

@@ -74,6 +74,9 @@ private InputNamespace BuildInputNamespaceInternal()
 
         private IReadOnlyDictionary<InputModelType, string> ResourceUpdateModelToResourceNameMap => _resourceUpdateModelToResourceNameMap ??= BuildResourceUpdateModelToResourceNameMap();
 
+        // If there're multiple API versions in the input namespace, use the last one as the default.
+        internal string DefaultApiVersion => InputNamespace.ApiVersions.Last();
+
         private IReadOnlyDictionary<InputModelType, string> BuildResourceUpdateModelToResourceNameMap()
         {
             Dictionary<InputModelType, string> map = new();

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/src/Providers/MockableResourceProvider.cs

@@ -85,8 +85,7 @@ private static Dictionary<InputClient, RestClientInfo> BuildRestClientInfos(IRea
                     ResourceHelpers.GetRestClientPropertyName(restClientProvider.Name),
                     new ExpressionPropertyBody(
                         restClientField.Assign(
-                            // TODO -- need to add apiVersion here in the future https://github.com/Azure/azure-sdk-for-net/issues/51791
-                            New.Instance(restClientProvider.Type, clientDiagnosticsProperty, thisResource.Pipeline(), thisResource.Endpoint(), Null),
+                            New.Instance(restClientProvider.Type, clientDiagnosticsProperty, thisResource.Pipeline(), thisResource.Endpoint(), Literal(ManagementClientGenerator.Instance.InputLibrary.DefaultApiVersion)),
                             nullCoalesce: true)),
                     enclosingType);
 

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/src/Providers/ResourceClientProvider.cs

@@ -239,7 +239,8 @@ private ConstructorProvider BuildResourceIdentifierConstructor()
             foreach (var (inputClient, clientInfo) in _clientInfos)
             {
                 bodyStatements.Add(clientInfo.DiagnosticsField.Assign(New.Instance(typeof(ClientDiagnostics), Literal(Type.Namespace), _resourceTypeField.As<ResourceType>().Namespace(), thisResource.Diagnostics())).Terminate());
-                bodyStatements.Add(clientInfo.RestClientField.Assign(New.Instance(clientInfo.RestClientProvider.Type, clientInfo.DiagnosticsField, thisResource.Pipeline(), thisResource.Endpoint(), apiVersion)).Terminate());
+                var effectiveApiVersion = apiVersion.NullCoalesce(Literal(ManagementClientGenerator.Instance.InputLibrary.DefaultApiVersion));
+                bodyStatements.Add(clientInfo.RestClientField.Assign(New.Instance(clientInfo.RestClientProvider.Type, clientInfo.DiagnosticsField, thisResource.Pipeline(), thisResource.Endpoint(), effectiveApiVersion)).Terminate());
             }
 
             bodyStatements.Add(Static(Type).As<ArmResource>().ValidateResourceId(idParameter).Terminate());

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/src/Providers/ResourceCollectionClientProvider.cs

@@ -16,6 +16,7 @@
 using Microsoft.TypeSpec.Generator.Providers;
 using Microsoft.TypeSpec.Generator.Snippets;
 using Microsoft.TypeSpec.Generator.Statements;
+using Microsoft.TypeSpec.Generator.Expressions;
 using System;
 using System.Collections;
 using System.Collections.Generic;
@@ -178,7 +179,8 @@ private ConstructorProvider BuildResourceIdentifierConstructor()
             foreach (var (inputClient, clientInfo) in _clientInfos)
             {
                 bodyStatements.Add(clientInfo.DiagnosticsField.Assign(New.Instance(typeof(ClientDiagnostics), Literal(Type.Namespace), _resourceTypeExpression.Namespace(), thisCollection.Diagnostics())).Terminate());
-                bodyStatements.Add(clientInfo.RestClientField.Assign(New.Instance(clientInfo.RestClientProvider.Type, clientInfo.DiagnosticsField, thisCollection.Pipeline(), thisCollection.Endpoint(), apiVersion)).Terminate());
+                var effectiveApiVersion = apiVersion.NullCoalesce(Literal(ManagementClientGenerator.Instance.InputLibrary.DefaultApiVersion));
+                bodyStatements.Add(clientInfo.RestClientField.Assign(New.Instance(clientInfo.RestClientProvider.Type, clientInfo.DiagnosticsField, thisCollection.Pipeline(), thisCollection.Endpoint(), effectiveApiVersion)).Terminate());
             }
 
             bodyStatements.Add(Static(Type).As<ArmCollection>().ValidateResourceId(idParameter).Terminate());

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/src/Snippets/ResourceMethodSnippets.cs

@@ -3,7 +3,6 @@
 
 using Azure.Core;
 using Azure.Core.Pipeline;
-using Azure.Generator.Management.Providers;
 using Azure.Generator.Management.Visitors;
 using Microsoft.TypeSpec.Generator.Expressions;
 using Microsoft.TypeSpec.Generator.Primitives;

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/test/Providers/TestData/ResourceClientProviderTests/Verify_ConstructorWithId.cs

@@ -1,4 +1,4 @@
 this.TryGetApiVersion(ResourceType, out string responseTypeApiVersion);
 _testClientClientDiagnostics = new global::Azure.Core.Pipeline.ClientDiagnostics("Samples", ResourceType.Namespace, this.Diagnostics);
-_testClientRestClient = new global::Samples.TestClient(_testClientClientDiagnostics, this.Pipeline, this.Endpoint, responseTypeApiVersion);
+_testClientRestClient = new global::Samples.TestClient(_testClientClientDiagnostics, this.Pipeline, this.Endpoint, (responseTypeApiVersion ?? "2023-01-01"));
 global::Samples.ResponseTypeResource.ValidateResourceId(id);

eng/packages/http-client-csharp-mgmt/generator/Azure.Generator.Management/test/TestHelpers/ManagementMockHelpers.cs

@@ -34,7 +34,7 @@ public static Mock<ManagementClientGenerator> LoadMockPlugin(
             HttpMessageApi? httpMessageApi = null,
             string? primaryNamespace = null)
         {
-            IReadOnlyList<string> inputNsApiVersions = apiVersions?.Invoke() ?? [];
+            IReadOnlyList<string> inputNsApiVersions = apiVersions?.Invoke() ?? ["2023-01-01"];
             IReadOnlyList<InputLiteralType> inputNsLiterals = inputLiterals?.Invoke() ?? [];
             IReadOnlyList<InputEnumType> inputNsEnums = inputEnums?.Invoke() ?? [];
             IReadOnlyList<InputClient> inputNsClients = clients?.Invoke() ?? [];