aspnetcore/src/Microsoft.AspNetCore.Razor.Language/Extensions/DesignTimeDirectivePass.cs

// 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 Microsoft.AspNetCore.Razor.Language.Intermediate;

namespace Microsoft.AspNetCore.Razor.Language.Extensions
{
    internal class DesignTimeDirectivePass : IntermediateNodePassBase, IRazorDirectiveClassifierPass
    {
        internal const string DesignTimeVariable = "__o";

        // This needs to run after other directive classifiers. Any DirectiveToken that is not removed 
        // by the previous classifiers will have auto-generated design time support.
        public override int Order => DefaultFeatureOrder;

        protected override void ExecuteCore(RazorCodeDocument codeDocument, DocumentIntermediateNode documentNode)
        {
            var walker = new DesignTimeHelperWalker();
            walker.VisitDocument(documentNode);
        }

        internal class DesignTimeHelperWalker : IntermediateNodeWalker
        {
            private DesignTimeDirectiveIntermediateNode _directiveNode;

            public override void VisitClassDeclaration(ClassDeclarationIntermediateNode node)
            {
                node.Children.Insert(0, new CSharpCodeIntermediateNode()
                {
                    Children =
                    {
                        new IntermediateToken()
                        {
                            Kind = TokenKind.CSharp,
                            Content = "#pragma warning disable 0414",
                        }
                    }
                });
                node.Children.Insert(1, new CSharpCodeIntermediateNode()
                {
                    Children =
                    {
                        new IntermediateToken()
                        {
                            Kind = TokenKind.CSharp,
                            Content = $"private static {typeof(object).FullName} {DesignTimeVariable} = null;",
                        }
                    }
                });
                node.Children.Insert(2, new CSharpCodeIntermediateNode()
                {
                    Children =
                    {
                        new IntermediateToken()
                        {
                            Kind = TokenKind.CSharp,
                            Content = "#pragma warning restore 0414",
                        }
                    }
                });

                _directiveNode = new DesignTimeDirectiveIntermediateNode();

                VisitDefault(node);

                node.Children.Insert(0, _directiveNode);
            }

            public override void VisitDirectiveToken(DirectiveTokenIntermediateNode node)
            {
                _directiveNode.Children.Add(node);
            }
        }
    }
}