feat: add TUnit0080 analyzer for missing polyfill types

TUnit.Analyzers.Tests/MissingPolyfillAnalyzerTests.cs

@@ -0,0 +1,51 @@
+using Microsoft.CodeAnalysis.Testing;
+using Verifier = TUnit.Analyzers.Tests.Verifiers.CSharpAnalyzerVerifier<TUnit.Analyzers.MissingPolyfillAnalyzer>;
+
+namespace TUnit.Analyzers.Tests;
+
+public class MissingPolyfillAnalyzerTests
+{
+    [Test]
+    public async Task No_Error_On_Modern_Tfm()
+    {
+        await Verifier
+            .VerifyAnalyzerAsync(
+                """
+                public class MyClass
+                {
+                }
+                """,
+                test =>
+                {
+                    test.TestState.AdditionalReferences.Clear();
+                }
+            );
+    }
+
+    [Test]
+    public async Task Error_When_ModuleInitializerAttribute_Missing()
+    {
+        var net48References = new ReferenceAssemblies(
+            "net48",
+            new PackageIdentity("Microsoft.NETFramework.ReferenceAssemblies.net48", "1.0.3"),
+            System.IO.Path.Combine("ref", "net48"));
+
+        await Verifier
+            .VerifyAnalyzerAsync(
+                """
+                public class MyClass
+                {
+                }
+                """,
+                test =>
+                {
+                    test.ReferenceAssemblies = net48References;
+                    test.TestState.AdditionalReferences.Clear();
+                    test.CompilerDiagnostics = CompilerDiagnostics.None;
+                },
+                Verifier
+                    .Diagnostic(Rules.MissingPolyfillPackage)
+                    .WithArguments("System.Runtime.CompilerServices.ModuleInitializerAttribute")
+            );
+    }
+}

TUnit.Analyzers/AnalyzerReleases.Unshipped.md

@@ -4,6 +4,7 @@ Rule ID | Category | Severity | Notes
 --------|----------|----------|-------
 TUnit0061 | Usage | Error | ClassDataSource type requires parameterless constructor
 TUnit0062 | Usage | Warning | CancellationToken must be the last parameter
+TUnit0073 | Usage | Error | Missing polyfill types required by TUnit
 
 ### Removed Rules
 

TUnit.Analyzers/MissingPolyfillAnalyzer.cs

@@ -0,0 +1,32 @@
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace TUnit.Analyzers;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class MissingPolyfillAnalyzer : ConcurrentDiagnosticAnalyzer
+{
+    private static readonly ImmutableArray<string> RequiredTypes =
+        ImmutableArray.Create("System.Runtime.CompilerServices.ModuleInitializerAttribute");
+
+    public override ImmutableArray<DiagnosticDescriptor> SupportedDiagnostics { get; } =
+        ImmutableArray.Create(Rules.MissingPolyfillPackage);
+
+    protected override void InitializeInternal(AnalysisContext context)
+    {
+        context.RegisterCompilationAction(AnalyzeCompilation);
+    }
+
+    private static void AnalyzeCompilation(CompilationAnalysisContext context)
+    {
+        foreach (var typeName in RequiredTypes)
+        {
+            if (context.Compilation.GetTypeByMetadataName(typeName) is null)
+            {
+                context.ReportDiagnostic(
+                    Diagnostic.Create(Rules.MissingPolyfillPackage, Location.None, typeName));
+            }
+        }
+    }
+}

TUnit.Analyzers/Resources.resx

@@ -525,6 +525,15 @@
     <data name="TUnit0052Title" xml:space="preserve">
         <value>Multiple constructors found without [TestConstructor] attribute</value>
     </data>
+    <data name="TUnit0073Description" xml:space="preserve">
+        <value>TUnit requires certain types (such as ModuleInitializerAttribute) that are not available on older target frameworks. Install the 'Polyfill' NuGet package to provide these types.</value>
+    </data>
+    <data name="TUnit0073MessageFormat" xml:space="preserve">
+        <value>Type '{0}' is required by TUnit but is not available. Install the 'Polyfill' NuGet package: dotnet add package Polyfill</value>
+    </data>
+    <data name="TUnit0073Title" xml:space="preserve">
+        <value>Missing polyfill types required by TUnit</value>
+    </data>
     <data name="TUnit0301Description" xml:space="preserve">
         <value>Tuple types require reflection for property/field access which is not AOT-compatible. Consider using concrete types or value deconstruction.</value>
     </data>

TUnit.Analyzers/Rules.cs

@@ -168,14 +168,20 @@ public static class Rules
     public static readonly DiagnosticDescriptor NoAccessibleConstructor =
         CreateDescriptor("TUnit0061", UsageCategory, DiagnosticSeverity.Error);
 
+    public static readonly DiagnosticDescriptor MissingPolyfillPackage =
+        CreateDescriptor("TUnit0073", UsageCategory, DiagnosticSeverity.Error,
+            customTags: [WellKnownDiagnosticTags.CompilationEnd],
+            helpLinkUri: "https://www.nuget.org/packages/Polyfill");
+
     public static readonly DiagnosticDescriptor GenericTypeNotAotCompatible =
         CreateDescriptor("TUnit0300", UsageCategory, DiagnosticSeverity.Warning);
 
     public static readonly DiagnosticDescriptor TupleNotAotCompatible =
         CreateDescriptor("TUnit0301", UsageCategory, DiagnosticSeverity.Warning);
 
 
-    private static DiagnosticDescriptor CreateDescriptor(string diagnosticId, string category, DiagnosticSeverity severity)
+    private static DiagnosticDescriptor CreateDescriptor(string diagnosticId, string category, DiagnosticSeverity severity,
+        string[]? customTags = null, string? helpLinkUri = null)
     {
         return new DiagnosticDescriptor(
             id: diagnosticId,
@@ -187,7 +193,9 @@ private static DiagnosticDescriptor CreateDescriptor(string diagnosticId, string
             defaultSeverity: severity,
             isEnabledByDefault: true,
             description: new LocalizableResourceString(diagnosticId + "Description", Resources.ResourceManager,
-                typeof(Resources))
+                typeof(Resources)),
+            helpLinkUri: helpLinkUri,
+            customTags: customTags ?? []
         );
     }
 }