fix: Adjust HR invocations to internal APIs

Use existing envvars to detect HR, use async initial HR for blazor-hotreload.js

Author: jeromelaban

src/Uno.Wasm.Bootstrap/ts/Uno/WebAssembly/HotReloadSupport.ts

@@ -33,7 +33,7 @@ namespace Uno.WebAssembly.Bootstrap {
 
 			// Take the place of the internal .NET for WebAssembly APIs for metadata updates coming
 			// from the "BrowserLink" feature.
-			const bootstrapContext = this._context;
+			const browserToolsVariable = (<any>this._context).config.environmentVariables['ASPNETCORE-BROWSER-TOOLS'];
 
 			(function (Blazor) {
 				Blazor._internal = {
@@ -45,21 +45,11 @@ namespace Uno.WebAssembly.Bootstrap {
 
 					applyExisting: async function (): Promise<void> {
 
-						var hotreloadConfigResponse = await fetch(`/_framework/unohotreload`);
-
-						var modifiableAssemblies = hotreloadConfigResponse.headers.get('DOTNET-MODIFIABLE-ASSEMBLIES');
-						var aspnetCoreBrowserTools = hotreloadConfigResponse.headers.get('ASPNETCORE-BROWSER-TOOLS');
-
-						if (modifiableAssemblies) {
-							bootstrapContext.MONO.mono_wasm_setenv('DOTNET_MODIFIABLE_ASSEMBLIES', modifiableAssemblies);
-						}
-
-						// To uncomment once https://github.com/dotnet/aspnetcore/issues/37357#issuecomment-941237000 is released
-						// if (aspnetCoreBrowserTools == "true")
+						if (browserToolsVariable == "true")
 						{
 							try {
 								var m = <any>await import(`/_framework/blazor-hotreload.js`);
-								m.receiveHotReload();
+								await m.receiveHotReloadAsync();
 							}
 							catch (e) {
 								console.error(`Failed to apply initial metadata delta ${e}`);
@@ -80,7 +70,7 @@ namespace Uno.WebAssembly.Bootstrap {
 			})((<any>window).Blazor || ((<any>window).Blazor = {}));
 
 			// Apply pending updates caused by a browser refresh
-			(<any>window).Blazor._internal.initialize(bootstrapContext.BINDING);
+			(<any>window).Blazor._internal.initialize();
 			await (<any>window).Blazor._internal.applyExisting();
 		}
 	}

src/Uno.Wasm.Sample/Program.cs

@@ -21,6 +21,11 @@
 using System.Globalization;
 using System.Runtime.InteropServices.JavaScript;
 using System.Threading.Tasks;
+using System.Reflection.Metadata;
+using Uno.Wasm.Sample;
+using System.Linq;
+
+[assembly: MetadataUpdateHandler(typeof(MyHandler))]
 
 namespace Uno.Wasm.Sample
 { 
@@ -81,6 +86,11 @@ static void Main(string[] args)
 			}, null, 5000, 5000);
 		}
 	}
+	public static class MyHandler
+	{
+		internal static void ClearCache(Type[]? types) => Console.WriteLine("MyHandler.ClearCache");
+		internal static void UpdateApplication(Type[]? types) => Console.WriteLine($"MyHandler.UpdateApplication {types.Length} types: {string.Join(", ", types.Select(t => t.Name	))}");
+	}
 
 #if NET7_0_OR_GREATER
 	public static partial class Imports