[http-client-csharp] Switch scaffolding to generate .slnx instead of .sln (#10234)

Fixes #4065
Fixes #10233

Per latest .NET guidelines, new projects should use the XML-based
`.slnx` solution format rather than the legacy `.sln` format.

### Changes

- **`NewProjectScaffolding.cs`**: Replace `.sln` generation with
`.slnx`. The verbose GUIDs-and-config `.sln` content is replaced with
the minimal XML format. Cleanup in `Execute()` now handles both `.sln`
(backward compat) and `.slnx`.
- **`CommandLineOptions.cs`**: Updated help text to reference `slnx`.
- **Test projects**: Regenerated all 72 test project solution files as
`.slnx`.

Generated `.slnx` output:

```xml
<Solution>
  <Project Path="src\PackageName.csproj" />
</Solution>
```

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: ArcturusZhang <10554446+ArcturusZhang@users.noreply.github.com>
Co-authored-by: Dapeng Zhang <dapzhang@microsoft.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: 3 people

cspell.yaml

@@ -247,6 +247,7 @@ words:
   - sfixed
   - shiki
   - sint
+  - slnx
   - snakeyaml
   - srnagar
   - ssdlrs

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/Primitives/NewProjectScaffolding.cs

@@ -9,12 +9,11 @@
 
 namespace Microsoft.TypeSpec.Generator.Primitives
 {
-    //TODO Need to define the rest of the extensibility points https://github.com/microsoft/typespec/issues/4065
     public class NewProjectScaffolding
     {
         public async Task<bool> Execute()
         {
-            //clean up old sln and csproj files
+            //clean up old sln, slnx and csproj files
             foreach (var file in Directory.GetFiles(CodeModelGenerator.Instance.Configuration.OutputDirectory, "*.csproj", SearchOption.AllDirectories))
             {
                 File.Delete(file);
@@ -23,14 +22,29 @@ public async Task<bool> Execute()
             {
                 File.Delete(file);
             }
+            foreach (var file in Directory.GetFiles(CodeModelGenerator.Instance.Configuration.OutputDirectory, "*.slnx", SearchOption.TopDirectoryOnly))
+            {
+                File.Delete(file);
+            }
 
             await WriteSolutionFiles();
 
             await WriteProjectFiles();
 
+            await WriteAdditionalFiles();
+
             return true;
         }
 
+        /// <summary>
+        /// Override this method to write additional files during new project scaffolding.
+        /// This is called after the solution and project files have been written.
+        /// </summary>
+        protected virtual Task WriteAdditionalFiles()
+        {
+            return Task.CompletedTask;
+        }
+
         private async Task WriteProjectFiles()
         {
             await File.WriteAllBytesAsync(
@@ -46,7 +60,7 @@ private string NormalizeLineEndings(string content)
         private async Task WriteSolutionFiles()
         {
             await File.WriteAllBytesAsync(
-                Path.Combine(CodeModelGenerator.Instance.Configuration.OutputDirectory, $"{CodeModelGenerator.Instance.Configuration.PackageName}.sln"),
+                Path.Combine(CodeModelGenerator.Instance.Configuration.OutputDirectory, $"{CodeModelGenerator.Instance.Configuration.PackageName}.slnx"),
                 Encoding.UTF8.GetBytes(NormalizeLineEndings(GetSolutionFileContent())));
         }
 
@@ -95,59 +109,11 @@ protected virtual string GetSourceProjectFileContent()
 
         protected virtual string GetSolutionFileContent()
         {
-            string slnContent = @"Microsoft Visual Studio Solution File, Format Version 12.00
-# Visual Studio Version 17
-VisualStudioVersion = 17.0.31903.59
-MinimumVisualStudioVersion = 10.0.40219.1
-";
-            slnContent += @"Project(""{{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}}"") = ""{0}"", ""src\{0}.csproj"", ""{{28FF4005-4467-4E36-92E7-DEA27DEB1519}}""
-EndProject
-";
-            slnContent += @"Global
-	GlobalSection(SolutionConfigurationPlatforms) = preSolution
-		Debug|Any CPU = Debug|Any CPU
-		Release|Any CPU = Release|Any CPU
-	EndGlobalSection
-	GlobalSection(ProjectConfigurationPlatforms) = postSolution
-		{{B0C276D1-2930-4887-B29A-D1A33E7009A2}}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{{B0C276D1-2930-4887-B29A-D1A33E7009A2}}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{{B0C276D1-2930-4887-B29A-D1A33E7009A2}}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{{B0C276D1-2930-4887-B29A-D1A33E7009A2}}.Release|Any CPU.Build.0 = Release|Any CPU
-		{{8E9A77AC-792A-4432-8320-ACFD46730401}}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{{8E9A77AC-792A-4432-8320-ACFD46730401}}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{{8E9A77AC-792A-4432-8320-ACFD46730401}}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{{8E9A77AC-792A-4432-8320-ACFD46730401}}.Release|Any CPU.Build.0 = Release|Any CPU
-";
-            slnContent += @"		{{A4241C1F-A53D-474C-9E4E-075054407E74}}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{{A4241C1F-A53D-474C-9E4E-075054407E74}}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{{A4241C1F-A53D-474C-9E4E-075054407E74}}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{{A4241C1F-A53D-474C-9E4E-075054407E74}}.Release|Any CPU.Build.0 = Release|Any CPU
-		{{FA8BD3F1-8616-47B6-974C-7576CDF4717E}}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{{FA8BD3F1-8616-47B6-974C-7576CDF4717E}}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{{FA8BD3F1-8616-47B6-974C-7576CDF4717E}}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{{FA8BD3F1-8616-47B6-974C-7576CDF4717E}}.Release|Any CPU.Build.0 = Release|Any CPU
-		{{85677AD3-C214-42FA-AE6E-49B956CAC8DC}}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{{85677AD3-C214-42FA-AE6E-49B956CAC8DC}}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{{85677AD3-C214-42FA-AE6E-49B956CAC8DC}}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{{85677AD3-C214-42FA-AE6E-49B956CAC8DC}}.Release|Any CPU.Build.0 = Release|Any CPU
-		{{28FF4005-4467-4E36-92E7-DEA27DEB1519}}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{{28FF4005-4467-4E36-92E7-DEA27DEB1519}}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{{28FF4005-4467-4E36-92E7-DEA27DEB1519}}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{{28FF4005-4467-4E36-92E7-DEA27DEB1519}}.Release|Any CPU.Build.0 = Release|Any CPU
-		{{1F1CD1D4-9932-4B73-99D8-C252A67D4B46}}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
-		{{1F1CD1D4-9932-4B73-99D8-C252A67D4B46}}.Debug|Any CPU.Build.0 = Debug|Any CPU
-		{{1F1CD1D4-9932-4B73-99D8-C252A67D4B46}}.Release|Any CPU.ActiveCfg = Release|Any CPU
-		{{1F1CD1D4-9932-4B73-99D8-C252A67D4B46}}.Release|Any CPU.Build.0 = Release|Any CPU
-	EndGlobalSection
-	GlobalSection(SolutionProperties) = preSolution
-		HideSolutionNode = FALSE
-	EndGlobalSection
-	GlobalSection(ExtensibilityGlobals) = postSolution
-		SolutionGuid = {{A97F4B90-2591-4689-B1F8-5F21FE6D6CAE}}
-	EndGlobalSection
-EndGlobal
-";
-            return string.Format(slnContent, CodeModelGenerator.Instance.Configuration.PackageName);
+            return string.Format(
+                @"<Solution>
+  <Project Path=""src\{0}.csproj"" />
+</Solution>
+", CodeModelGenerator.Instance.Configuration.PackageName);
         }
     }
 }

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/src/StartUp/CommandLineOptions.cs

@@ -18,7 +18,7 @@ internal class CommandLineOptions
         private const string CmdLineOutputDirectoryOptionHelpText = "The path to the directory containing the input files to the generator including the code model file and the configuration file for the generator.";
         private const string CmdLineDebugOptionHelpText = "Attempt to attach the debugger on execute.";
         private const string CmdLineGeneratorOptionHelpText = "The name of the generator to execute.";
-        private const string CmdLineNewProjectOptionHelpText = "Indicates if the generator should create the project files such as csproj, sln, etc.";
+        private const string CmdLineNewProjectOptionHelpText = "Indicates if the generator should create the project files such as csproj, slnx, etc.";
 
         /// <summary>
         /// The command line option to specify the path to the directory containing the input files to the generator.

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/Primitives/NewProjectScaffoldingTests.cs

@@ -0,0 +1,122 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System.IO;
+using System.Threading.Tasks;
+using Microsoft.TypeSpec.Generator.Primitives;
+using NUnit.Framework;
+
+namespace Microsoft.TypeSpec.Generator.Tests.Primitives
+{
+    internal class NewProjectScaffoldingTests
+    {
+        private string _outputDir = null!;
+
+        [SetUp]
+        public void SetUp()
+        {
+            _outputDir = Path.Combine(Path.GetTempPath(), Path.GetRandomFileName());
+            Directory.CreateDirectory(_outputDir);
+            Directory.CreateDirectory(Path.Combine(_outputDir, "src"));
+
+            MockHelpers.LoadMockGenerator(
+                outputPath: _outputDir,
+                configuration: "{\"package-name\": \"TestPackage\"}");
+        }
+
+        [TearDown]
+        public void TearDown()
+        {
+            if (Directory.Exists(_outputDir))
+            {
+                Directory.Delete(_outputDir, true);
+            }
+        }
+
+        [Test]
+        public async Task Execute_WritesSlnxAndCsprojFiles()
+        {
+            var scaffolding = new NewProjectScaffolding();
+            var result = await scaffolding.Execute();
+
+            Assert.IsTrue(result);
+            Assert.IsTrue(File.Exists(Path.Combine(_outputDir, "TestPackage.slnx")));
+            Assert.IsTrue(File.Exists(Path.Combine(_outputDir, "src", "TestPackage.csproj")));
+        }
+
+        [Test]
+        public async Task Execute_CleansUpOldSlnFiles()
+        {
+            // Create old .sln file
+            var oldSlnPath = Path.Combine(_outputDir, "OldProject.sln");
+            await File.WriteAllTextAsync(oldSlnPath, "old content");
+
+            var scaffolding = new NewProjectScaffolding();
+            await scaffolding.Execute();
+
+            Assert.IsFalse(File.Exists(oldSlnPath));
+        }
+
+        [Test]
+        public async Task Execute_CleansUpOldSlnxFiles()
+        {
+            // Create old .slnx file
+            var oldSlnxPath = Path.Combine(_outputDir, "OldProject.slnx");
+            await File.WriteAllTextAsync(oldSlnxPath, "old content");
+
+            var scaffolding = new NewProjectScaffolding();
+            await scaffolding.Execute();
+
+            Assert.IsFalse(File.Exists(oldSlnxPath));
+        }
+
+        [Test]
+        public async Task Execute_CallsWriteAdditionalFiles()
+        {
+            var scaffolding = new TestScaffolding();
+            var result = await scaffolding.Execute();
+
+            Assert.IsTrue(result);
+            Assert.IsTrue(scaffolding.WriteAdditionalFilesCalled);
+        }
+
+        [Test]
+        public async Task WriteAdditionalFiles_CanEmitCustomFiles()
+        {
+            var ciYmlPath = Path.Combine(_outputDir, "ci.yml");
+            var scaffolding = new FileWritingScaffolding(ciYmlPath, "name: CI");
+            await scaffolding.Execute();
+
+            Assert.IsTrue(File.Exists(ciYmlPath));
+            Assert.AreEqual("name: CI", await File.ReadAllTextAsync(ciYmlPath));
+        }
+
+        private class TestScaffolding : NewProjectScaffolding
+        {
+            public bool WriteAdditionalFilesCalled { get; private set; }
+
+            protected override Task WriteAdditionalFiles()
+            {
+                WriteAdditionalFilesCalled = true;
+                return Task.CompletedTask;
+            }
+        }
+
+        private class FileWritingScaffolding : NewProjectScaffolding
+        {
+            private readonly string _filePath;
+            private readonly string _content;
+
+            public FileWritingScaffolding(string filePath, string content)
+            {
+                _filePath = filePath;
+                _content = content;
+            }
+
+            protected override async Task WriteAdditionalFiles()
+            {
+                await File.WriteAllTextAsync(_filePath, _content);
+            }
+        }
+    }
+}

packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/SampleTypeSpec.sln

@@ -0,0 +1,3 @@
+<Solution>
+  <Project Path="src\SampleTypeSpec.csproj" />
+</Solution>

packages/http-client-csharp/generator/TestProjects/Local/Sample-TypeSpec/SampleTypeSpec.slnx

@@ -0,0 +1,3 @@
+<Solution>
+  <Project Path="src\Authentication.ApiKey.csproj" />
+</Solution>