Fix field naming and upgrade MTG (Azure#50732)

* Fix field naming and upgrade MTG

* regen

* missed regen

Author: JoshLove-msft

eng/Packages.Data.props

@@ -450,7 +450,7 @@
 
   <PropertyGroup>
     <TestProxyVersion>1.0.0-dev.20250501.1</TestProxyVersion>
-    <UnbrandedGeneratorVersion>1.0.0-alpha.20250618.1</UnbrandedGeneratorVersion>
+    <UnbrandedGeneratorVersion>1.0.0-alpha.20250619.2</UnbrandedGeneratorVersion>
     <AzureGeneratorVersion>1.0.0-alpha.20250527.2</AzureGeneratorVersion>
   </PropertyGroup>
 </Project>

eng/packages/http-client-csharp/generator/Azure.Generator/src/Properties/launchSettings.json

@@ -50,6 +50,11 @@
       "commandName": "Executable",
       "executablePath": "dotnet"
     },
+    "http-azure-resource-manager-large-header": {
+      "commandLineArgs": "$(SolutionDir)/../dist/generator/Microsoft.TypeSpec.Generator.dll $(SolutionDir)/TestProjects/Spector/http/azure/resource-manager/large-header -g AzureStubGenerator",
+      "commandName": "Executable",
+      "executablePath": "dotnet"
+    },
     "http-azure-special-headers-client-request-id": {
       "commandLineArgs": "$(SolutionDir)/../dist/generator/Microsoft.TypeSpec.Generator.dll $(SolutionDir)/TestProjects/Spector/http/azure/special-headers/client-request-id -g AzureStubGenerator",
       "commandName": "Executable",

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

@@ -84,7 +84,7 @@ public CollectionResultDefinition(ClientProvider client, InputPagingServiceMetho
                 var field = new FieldProvider(
                     FieldModifiers.Private | FieldModifiers.ReadOnly,
                     parameter.Type,
-                    $"_{parameter.Name}",
+                    $"_{parameter.Name.ToVariableName()}",
                     this);
                 fields.Add(field);
                 if (field.Name == "_context")

eng/packages/http-client-csharp/generator/Azure.Generator/test/Providers/CollectionResultDefinitions/NextLinkTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
+using System.Collections.Generic;
 using Azure.Generator.Providers;
 using Azure.Generator.Tests.Common;
 using Azure.Generator.Tests.TestHelpers;
@@ -153,6 +154,42 @@ public void NextLinkInBodyMultipleClients()
             Assert.IsNotNull(felineClientCollectionResult);
         }
 
+        [Test]
+        public void UsesValidFieldIdentifierNames()
+        {
+            MockHelpers.LoadMockPlugin();
+            var inputModel = InputFactory.Model("cat", properties:
+            [
+                InputFactory.Property("color", InputPrimitiveType.String, isRequired: true),
+            ]);
+            var pagingMetadata = InputFactory.NextLinkPagingMetadata("cats", "nextCat", InputResponseLocation.Body);
+            var response = InputFactory.OperationResponse(
+                [200],
+                InputFactory.Model(
+                    "page",
+                    properties:
+                    [
+                        InputFactory.Property("cats", InputFactory.Array(inputModel)),
+                        InputFactory.Property("nextCat", InputPrimitiveType.Url)
+                    ]));
+            IReadOnlyList<InputParameter> parameters =
+            [
+                InputFactory.Parameter("$foo", InputPrimitiveType.String, isRequired: true,
+                    location: InputRequestLocation.Header)
+            ];
+            var operation = InputFactory.Operation("getCats", responses: [response], parameters: parameters);
+            var inputServiceMethod = InputFactory.PagingServiceMethod("getCats", operation,
+                pagingMetadata: pagingMetadata, parameters: parameters);
+            var catClient = InputFactory.Client("catClient", methods: [inputServiceMethod], clientNamespace: "Cats");
+            var clientProvider = AzureClientGenerator.Instance.TypeFactory.CreateClient(catClient);
+            var modelType = AzureClientGenerator.Instance.TypeFactory.CreateModel(inputModel);
+            var collectionResultDefinition =
+                new CollectionResultDefinition(clientProvider!, inputServiceMethod, modelType!.Type, false);
+            var fields = collectionResultDefinition.Fields;
+
+            Assert.IsTrue(fields.Any(f => f.Name == "_foo"));
+        }
+
         private static void CreatePagingOperation(InputResponseLocation responseLocation)
         {
             var inputModel = InputFactory.Model("cat", properties: