[Blazor] Pass environment to runtime config only when defined (dotnet#62418)

Author: maraf

src/Components/Web.JS/src/Platform/Mono/MonoPlatform.ts

@@ -138,9 +138,12 @@ function prepareRuntimeConfig(options: Partial<WebAssemblyStartOptions>, onConfi
   const config: MonoConfig = {
     maxParallelDownloads: 1000000, // disable throttling parallel downloads
     enableDownloadRetry: false, // disable retry downloads
-    applicationEnvironment: options.environment,
   };
 
+  if (options.environment) {
+    config.applicationEnvironment = options.environment;
+  }
+
   const onConfigLoaded = async (loadedConfig: MonoConfig) => {
     if (!loadedConfig.environmentVariables) {
       loadedConfig.environmentVariables = {};

src/Components/test/E2ETest/Tests/WebAssemblyEnvironmentTest.cs

@@ -0,0 +1,32 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.Globalization;
+using GlobalizationWasmApp;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
+using Microsoft.AspNetCore.E2ETesting;
+using OpenQA.Selenium;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Components.E2ETest.Tests;
+
+public class WebAssemblyEnvironmentTest : ServerTestBase<ToggleExecutionModeServerFixture<Program>>
+{
+    public WebAssemblyEnvironmentTest(
+        BrowserFixture browserFixture,
+        ToggleExecutionModeServerFixture<Program> serverFixture,
+        ITestOutputHelper output)
+        : base(browserFixture, serverFixture, output)
+    {
+    }
+
+    [Fact]
+    public void WebAssemblyEnvironment_Works()
+    {
+        Navigate($"{ServerPathBase}/");
+
+        // Verify that the environment gets detected as 'Staging'.
+        Browser.Equal("Staging", () => Browser.FindElement(By.Id("environment")).Text);
+    }
+}

src/Components/test/testassets/GlobalizationWasmApp/App.razor

@@ -6,3 +6,5 @@
 <p>DateTime: <span id="dateTime">@(new DateTime(2020, 09, 02))</span></p>
 
 <p>Localized string: <span id="localizedString">@Loc["Hello"]</span></p>
+
+<WebAssemblyEnvironment />

src/Components/test/testassets/GlobalizationWasmApp/GlobalizationWasmApp.csproj

@@ -7,6 +7,8 @@
 
     <!-- Resx generation on Resources.resx only -->
     <GenerateResxSource>false</GenerateResxSource>
+
+    <WasmApplicationEnvironmentName>Staging</WasmApplicationEnvironmentName>
   </PropertyGroup>
 
   <PropertyGroup Condition="'$(TestTrimmedOrMultithreadingApps)' == 'true'">

src/Components/test/testassets/GlobalizationWasmApp/WebAssemblyEnvironment.razor

@@ -0,0 +1,3 @@
+@inject Microsoft.AspNetCore.Components.WebAssembly.Hosting.IWebAssemblyHostEnvironment HostEnvironment
+
+<div id="environment">@HostEnvironment.Environment</div>