feat: add TUnit0080 analyzer for missing polyfill types

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
+TUnit0080 | Usage | Error | Missing polyfill types required by TUnit
 
 ### Removed Rules
 

TUnit.Analyzers/MissingPolyfillAnalyzer.cs

@@ -0,0 +1,34 @@
+using System.Collections.Immutable;
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Diagnostics;
+
+namespace TUnit.Analyzers;
+
+[DiagnosticAnalyzer(LanguageNames.CSharp)]
+public class MissingPolyfillAnalyzer : ConcurrentDiagnosticAnalyzer
+{
+    private static readonly string[] RequiredTypes =
+    [
+        "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="TUnit0080Description" 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="TUnit0080MessageFormat" 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="TUnit0080Title" 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

@@ -168,6 +168,9 @@ public static class Rules
     public static readonly DiagnosticDescriptor NoAccessibleConstructor =
         CreateDescriptor("TUnit0061", UsageCategory, DiagnosticSeverity.Error);
 
+    public static readonly DiagnosticDescriptor MissingPolyfillPackage =
+        CreateDescriptor("TUnit0080", UsageCategory, DiagnosticSeverity.Error);
+
     public static readonly DiagnosticDescriptor GenericTypeNotAotCompatible =
         CreateDescriptor("TUnit0300", UsageCategory, DiagnosticSeverity.Warning);