Rely on Razors MalformedDirective identification for @page.

aspnet/Razor#1448

src/Microsoft.AspNetCore.Mvc.RazorPages/Infrastructure/PageDirectiveFeature.cs

@@ -50,20 +50,16 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
             var documentIRNode = codeDocument.GetDocumentIntermediateNode();
             if (PageDirective.TryGetPageDirective(documentIRNode, out var pageDirective))
             {
+                if (pageDirective.DirectiveNode is MalformedDirectiveIntermediateNode malformedNode)
+                {
+                    logger.MalformedPageDirective(sourceDocument.FilePath, malformedNode.Diagnostics);
+                }
+
                 template = pageDirective.RouteTemplate;
                 return true;
             }
 
             template = null;
-
-            var visitor = new Visitor();
-            visitor.Visit(documentIRNode);
-            if (visitor.MalformedPageDirective != null)
-            {
-                logger.MalformedPageDirective(sourceDocument.FilePath, visitor.MalformedPageDirective.Diagnostics);
-                return true;
-            }
-
             return false;
         }
 
@@ -76,18 +72,5 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure
                 options.ParseOnlyLeadingDirectives = true;
             }
         }
-
-        private class Visitor : IntermediateNodeWalker
-        {
-            public MalformedDirectiveIntermediateNode MalformedPageDirective { get; private set; }
-
-            public override void VisitMalformedDirective(MalformedDirectiveIntermediateNode node)
-            {
-                if (node.Descriptor == PageDirective.Directive)
-                {
-                    MalformedPageDirective = node;
-                }
-            }
-        }
     }
 }