Emit diagnostics for unsupported RDG scenarios (#49417)

* Emit diagnostics for unsupported RDG scenarios

* Add test for invalid/valid endpoints

Author: captainsafia

src/Http/Http.Extensions/gen/DiagnosticDescriptors.cs

@@ -90,4 +90,20 @@ internal static class DiagnosticDescriptors
         "Usage",
         DiagnosticSeverity.Error,
         isEnabledByDefault: true);
+
+    public static DiagnosticDescriptor TypeParametersNotSupported { get; } = new(
+        "RDG011",
+        new LocalizableResourceString(nameof(Resources.TypeParametersNotSupported_Title), Resources.ResourceManager, typeof(Resources)),
+        new LocalizableResourceString(nameof(Resources.TypeParametersNotSupported_Message), Resources.ResourceManager, typeof(Resources)),
+        "Usage",
+        DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
+
+    public static DiagnosticDescriptor InaccessibleTypesNotSupported { get; } = new(
+        "RDG012",
+        new LocalizableResourceString(nameof(Resources.InaccessibleTypesNotSupported_Title), Resources.ResourceManager, typeof(Resources)),
+        new LocalizableResourceString(nameof(Resources.InaccessibleTypesNotSupported_Message), Resources.ResourceManager, typeof(Resources)),
+        "Usage",
+        DiagnosticSeverity.Error,
+        isEnabledByDefault: true);
 }

src/Http/Http.Extensions/gen/Resources.resx

@@ -177,4 +177,16 @@
   <data name="InvalidAsParametersNullable_Message" xml:space="preserve">
     <value>The nullable type '{0}' is not supported. Mark the parameter as non-nullable.</value>
   </data>
+  <data name="TypeParametersNotSupported_Title" xml:space="preserve">
+    <value>Type parameters not supported</value>
+  </data>
+  <data name="TypeParametersNotSupported_Message" xml:space="preserve">
+    <value>Endpoints with generic type parameters are not supported. Compile-time endpoint generation will skip this endpoint.</value>
+  </data>
+  <data name="InaccessibleTypesNotSupported_Title" xml:space="preserve">
+    <value>Unable to resolve inaccessible type</value>
+  </data>
+  <data name="InaccessibleTypesNotSupported_Message" xml:space="preserve">
+    <value>Encountered inaccessible type '{0}' while processing endpoint. Compile-time endpoint generation will skip this endpoint.</value>
+  </data>
 </root>

src/Http/Http.Extensions/gen/StaticRouteHandlerModel/Emitters/DiagnosticEmitter.cs

@@ -0,0 +1,48 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis;
+
+namespace Microsoft.AspNetCore.Http.RequestDelegateGenerator.StaticRouteHandlerModel;
+
+internal static class DiagnosticEmitter
+{
+    public static void EmitRequiredDiagnostics(this EndpointResponse response, List<Diagnostic> diagnostics, Location location)
+    {
+        if (response.ResponseType is ITypeParameterSymbol)
+        {
+            diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.TypeParametersNotSupported, location));
+        }
+
+        if (response.ResponseType?.DeclaredAccessibility is Accessibility.Private or Accessibility.Protected)
+        {
+            diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.InaccessibleTypesNotSupported, location));
+        }
+
+        if (response.ResponseType?.IsAnonymousType == true)
+        {
+            diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.UnableToResolveAnonymousReturnType, location));
+        }
+    }
+
+    public static void EmitRequiredDiagnostics(this IParameterSymbol parameterSymbol, List<Diagnostic> diagnostics, Location location)
+    {
+        var typeSymbol = parameterSymbol.Type;
+        if (typeSymbol is ITypeParameterSymbol ||
+            typeSymbol is INamedTypeSymbol &&
+            ((INamedTypeSymbol)typeSymbol).TypeArguments.Any(a => a is ITypeParameterSymbol))
+        {
+            diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.TypeParametersNotSupported, location));
+        }
+
+        if (typeSymbol.DeclaredAccessibility is Accessibility.Private or Accessibility.Protected ||
+            typeSymbol is INamedTypeSymbol &&
+            ((INamedTypeSymbol)typeSymbol).TypeArguments.Any(typeArg =>
+                typeArg.DeclaredAccessibility is Accessibility.Private or Accessibility.Protected))
+        {
+            diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.InaccessibleTypesNotSupported, location, typeSymbol.Name));
+        }
+    }
+}

src/Http/Http.Extensions/gen/StaticRouteHandlerModel/Endpoint.cs

@@ -29,12 +29,7 @@ public Endpoint(IInvocationOperation operation, WellKnownTypes wellKnownTypes, S
         }
 
         Response = new EndpointResponse(method, wellKnownTypes);
-        if (Response.IsAnonymousType)
-        {
-            Diagnostics.Add(Diagnostic.Create(DiagnosticDescriptors.UnableToResolveAnonymousReturnType, Operation.Syntax.GetLocation()));
-            return;
-        }
-
+        Response.EmitRequiredDiagnostics(Diagnostics, Operation.Syntax.GetLocation());
         IsAwaitable = Response?.IsAwaitable == true;
 
         EmitterContext.HasResponseMetadata = Response is { } response && !(response.IsIResult || response.HasNoResponse);
@@ -55,7 +50,13 @@ public Endpoint(IInvocationOperation operation, WellKnownTypes wellKnownTypes, S
 
         for (var i = 0; i < method.Parameters.Length; i++)
         {
-            var parameter = new EndpointParameter(this, method.Parameters[i], wellKnownTypes);
+            var parameterSymbol = method.Parameters[i];
+            parameterSymbol.EmitRequiredDiagnostics(Diagnostics, Operation.Syntax.GetLocation());
+            if (Diagnostics.Count > 0)
+            {
+                continue;
+            }
+            var parameter = new EndpointParameter(this, parameterSymbol, wellKnownTypes);
 
             switch (parameter.Source)
             {
@@ -82,6 +83,7 @@ public Endpoint(IInvocationOperation operation, WellKnownTypes wellKnownTypes, S
         Parameters = parameters;
 
         EmitterContext.RequiresLoggingHelper = !Parameters.All(parameter =>
+            parameter is not null &&
             parameter.Source == EndpointParameterSource.SpecialType ||
             parameter is { IsArray: true, ElementType.SpecialType: SpecialType.System_String, Source: EndpointParameterSource.Query });
     }

src/Http/Http.Extensions/gen/StaticRouteHandlerModel/EndpointResponse.cs

@@ -20,7 +20,6 @@ internal class EndpointResponse
     public bool HasNoResponse { get; set; }
     public bool IsIResult { get; set; }
     public bool IsSerializable { get; set; }
-    public bool IsAnonymousType { get; set; }
     public bool IsEndpointMetadataProvider { get; set; }
     private WellKnownTypes WellKnownTypes { get; init; }
 
@@ -34,7 +33,6 @@ internal EndpointResponse(IMethodSymbol method, WellKnownTypes wellKnownTypes)
         IsIResult = GetIsIResult();
         IsSerializable = GetIsSerializable();
         ContentType = GetContentType();
-        IsAnonymousType = method.ReturnType.IsAnonymousType;
         IsEndpointMetadataProvider = ImplementsIEndpointMetadataProvider(ResponseType, wellKnownTypes);
     }