Ensure @typeparam directive descriptor is always set (#33456)

* Ensure @typeparam directive descriptor is always set
* Set fallback RazorLang value for test scenarios

Author: captainsafia

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentConstrainedTypeParamDirective.cs

@@ -0,0 +1,32 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNetCore.Razor.Language.Components
+{
+    internal class ComponentConstrainedTypeParamDirective
+    {
+        public static DirectiveDescriptor Directive = DirectiveDescriptor.CreateDirective(
+            "typeparam",
+            DirectiveKind.SingleLine,
+            builder =>
+            {
+                builder.AddMemberToken(ComponentResources.TypeParamDirective_Token_Name, ComponentResources.TypeParamDirective_Token_Description);
+                builder.AddOptionalGenericTypeConstraintToken(ComponentResources.TypeParamDirective_Constraint_Name, ComponentResources.TypeParamDirective_Constraint_Description);
+                builder.Usage = DirectiveUsage.FileScopedMultipleOccurring;
+                builder.Description = ComponentResources.TypeParamDirective_Description;
+            });
+
+        public static RazorProjectEngineBuilder Register(RazorProjectEngineBuilder builder)
+        {
+            if (builder == null)
+            {
+                throw new ArgumentNullException(nameof(builder));
+            }
+
+            builder.AddDirective(Directive, FileKinds.Component, FileKinds.ComponentImport);
+            return builder;
+        }
+    }
+}

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentDocumentClassifierPass.cs

@@ -100,7 +100,12 @@ protected override void OnDocumentStructureCreated(
             {
                 @class.BaseType = ComponentsApi.ComponentBase.FullTypeName;
 
-                var typeParamReferences = documentNode.FindDirectiveReferences(ComponentTypeParamDirective.Directive);
+                // Constrained type parameters are only supported in Razor language versions v6.0
+                var razorLanguageVersion = codeDocument.GetParserOptions()?.Version ?? RazorLanguageVersion.Latest;
+                var directiveType = razorLanguageVersion.CompareTo(RazorLanguageVersion.Version_6_0) >= 0
+                    ? ComponentConstrainedTypeParamDirective.Directive
+                    : ComponentTypeParamDirective.Directive;
+                var typeParamReferences = documentNode.FindDirectiveReferences(directiveType);
                 for (var i = 0; i < typeParamReferences.Count; i++)
                 {
                     var typeParamNode = (DirectiveIntermediateNode)typeParamReferences[i].Node;

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentTypeParamDirective.cs

@@ -7,45 +7,23 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
 {
     internal class ComponentTypeParamDirective
     {
-        public static DirectiveDescriptor Directive;
+        public static DirectiveDescriptor Directive = DirectiveDescriptor.CreateDirective(
+            "typeparam",
+            DirectiveKind.SingleLine,
+            builder =>
+            {
+                builder.AddMemberToken(ComponentResources.TypeParamDirective_Token_Name, ComponentResources.TypeParamDirective_Token_Description);
+                builder.Usage = DirectiveUsage.FileScopedMultipleOccurring;
+                builder.Description = ComponentResources.TypeParamDirective_Description;
+            });
 
-        public static RazorProjectEngineBuilder Register(RazorProjectEngineBuilder builder, bool supportConstraints)
+        public static RazorProjectEngineBuilder Register(RazorProjectEngineBuilder builder)
         {
             if (builder == null)
             {
                 throw new ArgumentNullException(nameof(builder));
             }
 
-            if (Directive == null)
-            {
-                // Do nothing and assume the first registration wins. In real life this directive is only ever registered once.
-                if (supportConstraints)
-                {
-                    Directive = DirectiveDescriptor.CreateDirective(
-                        "typeparam",
-                        DirectiveKind.SingleLine,
-                        builder =>
-                        {
-                            builder.AddMemberToken(ComponentResources.TypeParamDirective_Token_Name, ComponentResources.TypeParamDirective_Token_Description);
-                            builder.AddOptionalGenericTypeConstraintToken(ComponentResources.TypeParamDirective_Constraint_Name, ComponentResources.TypeParamDirective_Constraint_Description);
-                            builder.Usage = DirectiveUsage.FileScopedMultipleOccurring;
-                            builder.Description = ComponentResources.TypeParamDirective_Description;
-                        });
-                }
-                else
-                {
-                    Directive = DirectiveDescriptor.CreateDirective(
-                        "typeparam",
-                        DirectiveKind.SingleLine,
-                        builder =>
-                        {
-                            builder.AddMemberToken(ComponentResources.TypeParamDirective_Token_Name, ComponentResources.TypeParamDirective_Token_Description);
-                            builder.Usage = DirectiveUsage.FileScopedMultipleOccurring;
-                            builder.Description = ComponentResources.TypeParamDirective_Description;
-                        });
-                }
-            }
-
             builder.AddDirective(Directive, FileKinds.Component, FileKinds.ComponentImport);
             return builder;
         }

src/Razor/Microsoft.AspNetCore.Razor.Language/src/RazorProjectEngine.cs

@@ -222,12 +222,16 @@ private static void AddComponentFeatures(RazorProjectEngineBuilder builder, Razo
             ComponentLayoutDirective.Register(builder);
             ComponentPageDirective.Register(builder);
 
-            // Unconditionally enable the feature for the time being until we flow the SDK with the flow version
-            // into the repository.
-            ComponentTypeParamDirective.Register(
-                builder,
-                supportConstraints: true);
-                //supportConstraints: razorLanguageVersion.CompareTo(RazorLanguageVersion.Version_6_0) >= 0);
+
+
+            if (razorLanguageVersion.CompareTo(RazorLanguageVersion.Version_6_0) >= 0)
+            {
+                ComponentConstrainedTypeParamDirective.Register(builder);
+            }
+            else
+            {
+                ComponentTypeParamDirective.Register(builder);
+            }
 
             if (razorLanguageVersion.CompareTo(RazorLanguageVersion.Version_5_0) >= 0)
             {