Moved all extension methods into extension blocks (#1155)

app/Tests/Analyzers/ClassicExtensionMethodAnalyzerTests.cs

@@ -0,0 +1,69 @@
+using AIStudio.Tests.Models.Generation;
+
+using Microsoft.CodeAnalysis;
+
+using SourceCodeRules.StyleAnalyzers;
+
+namespace AIStudio.Tests.Analyzers;
+
+/// <summary>
+/// Checks that extension methods are declared in extension blocks, not with a this parameter.
+/// </summary>
+/// <remarks>
+/// AI Studio declares all its extension members in extension blocks, one per receiver. MWAIS0016 refuses the
+/// classic form while compiling, except for a method with a params parameter: for a member of an extension
+/// block, the compiler of the .NET 10.0.1xx SDK warns about every argument passed one by one to a params
+/// parameter (CS8620, dotnet/roslyn#80024).
+/// </remarks>
+[TestFixture]
+public sealed class ClassicExtensionMethodAnalyzerTests
+{
+    [TestCase("public static string Label(this Meeting meeting) => meeting.Name;", "Label", TestName = "A public extension method")]
+    [TestCase("private static string Label(this Meeting meeting) => meeting.Name;", "Label", TestName = "A private extension method")]
+    [TestCase("public static string Label(this Meeting meeting, string prefix) => prefix + meeting.Name;", "Label", TestName = "An extension method with further parameters")]
+    [TestCase("public static T Echo<T>(this T value) where T : class => value;", "Echo", TestName = "A generic extension method")]
+    [TestCase("public static void Bump(this ref int value) => value++;", "Bump", TestName = "An extension method with a ref receiver")]
+    [TestCase("public static System.Threading.Tasks.Task<string> LabelAsync(this Meeting meeting) => System.Threading.Tasks.Task.FromResult(meeting.Name);", "LabelAsync", TestName = "An asynchronous extension method")]
+    public async Task AClassicExtensionMethodIsRefused(string member, string name)
+    {
+        var reported = await AnalyzeAsync(member);
+
+        using (Assert.EnterMultipleScope())
+        {
+            Assert.That(reported, Has.Count.EqualTo(1));
+            Assert.That(reported.FirstOrDefault()?.Id, Is.EqualTo("MWAIS0016"));
+            Assert.That(reported.FirstOrDefault()?.GetMessage(), Does.Contain($"'{name}'"));
+        }
+    }
+
+    [TestCase("extension(Meeting meeting) { public string Label() => meeting.Name; }", TestName = "A member of an extension block")]
+    [TestCase("extension<T>(T value) where T : class { public T Echo() => value; }", TestName = "A member of a generic extension block")]
+    [TestCase("public static string Label(Meeting meeting) => meeting.Name;", TestName = "A static method without a this parameter")]
+    [TestCase("public static string Label(this Meeting meeting, params string[] prefixes) => string.Concat(prefixes) + meeting.Name;", TestName = "An extension method with a params parameter")]
+    public async Task AnythingElseIsLeftAlone(string member)
+    {
+        var reported = await AnalyzeAsync(member);
+
+        Assert.That(reported, Is.Empty);
+    }
+
+    private static async Task<IReadOnlyList<Diagnostic>> AnalyzeAsync(string member)
+    {
+        var source =
+            $$"""
+              namespace Sample;
+
+              public sealed class Meeting
+              {
+                  public string Name { get; set; } = "Kickoff";
+              }
+
+              public static class MeetingExtensions
+              {
+                  {{member}}
+              }
+              """;
+
+        return await CompilationHarness.AnalyzeAsync(source, new ClassicExtensionMethodAnalyzer());
+    }
+}