In RazorCompiler, have BuildRenderTree overrides call base implementation

src/Microsoft.AspNetCore.Blazor.Build/Core/RazorCompilation/Engine/BlazorLoweringPhase.cs

@@ -1,6 +1,7 @@
 // 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.Blazor.Components;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.CodeGeneration;
 using Microsoft.AspNetCore.Razor.Language.Intermediate;
@@ -28,10 +29,33 @@ namespace Microsoft.AspNetCore.Blazor.Build.Core.RazorCompilation.Engine
         {
             var writer = BlazorComponentDocumentWriter.Create(_codegenOptions);
             var documentNode = codeDocument.GetDocumentIntermediateNode();
+            ConvertToBlazorPrimaryMethod(documentNode);
             var csharpDoc = writer.WriteDocument(codeDocument, documentNode);
             codeDocument.SetCSharpDocument(csharpDoc);
         }
 
+        private void ConvertToBlazorPrimaryMethod(DocumentIntermediateNode documentNode)
+        {
+            // Replaces the default "ExecuteAsync" method with Blazor's "BuildRenderTree".
+            // Note that DefaultDocumentWriter's VisitMethodDeclaration is hardcoded to
+            // emit methods with no parameters, so there's no way of setting the parameters
+            // from here. We inject the parameter later in RazorCompiler.
+            var primaryMethod = documentNode.FindPrimaryMethod();
+            primaryMethod.ReturnType = "void";
+            primaryMethod.MethodName = nameof(BlazorComponent.BuildRenderTree);
+            primaryMethod.Modifiers.Clear();
+            primaryMethod.Modifiers.Add("public");
+            primaryMethod.Modifiers.Add("override");
+
+            var line = new CSharpCodeIntermediateNode();
+            line.Children.Add(new IntermediateToken
+            {
+                Kind = TokenKind.CSharp,
+                Content = $"base.{primaryMethod.MethodName}(builder);" + Environment.NewLine
+            });
+            primaryMethod.Children.Insert(0, line);
+        }
+
         /// <summary>
         /// Creates <see cref="DocumentWriter"/> instances that are configured to use
         /// <see cref="BlazorCodeTarget"/>.

src/Microsoft.AspNetCore.Blazor.Build/Core/RazorCompilation/RazorCompiler.cs

@@ -102,9 +102,13 @@ namespace Microsoft.AspNetCore.Blazor.Build.Core.RazorCompilation
                 engine.Process(codeDoc);
                 var csharpDocument = codeDoc.GetCSharpDocument();
                 var generatedCode = csharpDocument.GeneratedCode;
+
+                // Add parameters to the primary method via string manipulation because
+                // DefaultDocumentWriter's VisitMethodDeclaration can't emit parameters
+                var primaryMethodSource = $"public override void {nameof(BlazorComponent.BuildRenderTree)}";
                 generatedCode = generatedCode.Replace(
-                    "public async override global::System.Threading.Tasks.Task ExecuteAsync()",
+                    $"{primaryMethodSource}()",
-                    $"public override void {nameof(BlazorComponent.BuildRenderTree)}({typeof(RenderTreeBuilder).FullName} builder)");
+                    $"{primaryMethodSource}({typeof(RenderTreeBuilder).FullName} builder)");
 
                 resultOutput.WriteLine(generatedCode);