Support JsonStringEnumConverter. Fixes #19086 (#20446)

* Fix serializing enums. Fixes #19086

* Add E2E test

src/Components/WebAssembly/Build/src/targets/BuiltInBclLinkerDescriptor.xml

@@ -24,4 +24,15 @@
     <type fullname="WebAssembly.Net.Http.HttpClient.FetchCredentialsOption" />
     <type fullname="WebAssembly.Net.Http.HttpClient.WasmHttpMessageHandler" />
   </assembly>
+
+  <assembly fullname="System.Text.Json">
+    <!-- S.T.J. uses Activator.CreateInstance to instantiate converters, so we need to preserve default constructors.
+    For safety, do this for all converter types, even though most of them are preserved anyway due to being referenced
+    statically. It's only JsonStringEnumConverter that currently isn't referenced statically.
+    The following is a workaround for https://github.com/dotnet/aspnetcore/issues/19086.
+    The underlying issue is reported in the runtime repo at https://github.com/dotnet/runtime/issues/34449 -->
+    <type fullname="System.Text.Json.Serialization.*Converter">
+      <method signature="System.Void .ctor()" />
+    </type>
+  </assembly>
 </linker>

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

@@ -0,0 +1,39 @@
+// 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 BasicTestApp;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure;
+using Microsoft.AspNetCore.Components.E2ETest.Infrastructure.ServerFixtures;
+using Microsoft.AspNetCore.E2ETesting;
+using OpenQA.Selenium;
+using Xunit;
+using Xunit.Abstractions;
+
+namespace Microsoft.AspNetCore.Components.E2ETest.Tests
+{
+    public class JsonSerializationTest : ServerTestBase<ToggleExecutionModeServerFixture<Program>>
+    {
+        public JsonSerializationTest(
+            BrowserFixture browserFixture,
+            ToggleExecutionModeServerFixture<Program> serverFixture,
+            ITestOutputHelper output)
+            : base(browserFixture, serverFixture, output)
+        {
+        }
+
+        protected override void InitializeAsyncCore()
+        {
+            Navigate(ServerPathBase, noReload: _serverFixture.ExecutionMode == ExecutionMode.Client);
+            Browser.MountTestComponent<JsonSerializationCases>();
+            Browser.Exists(By.Id("json-serialization-cases"));
+        }
+
+        [Fact]
+        public void JsonSerializationCasesWork()
+        {
+            Browser.Equal("Lord Smythe", () => Browser.FindElement(By.Id("deserialized-name")).Text);
+            Browser.Equal("68", () => Browser.FindElement(By.Id("deserialized-age")).Text);
+            Browser.Equal("Vexed", () => Browser.FindElement(By.Id("deserialized-mood")).Text);
+        }
+    }
+}

src/Components/test/testassets/BasicTestApp/Index.razor

@@ -46,6 +46,7 @@
         <option value="BasicTestApp.InputEventComponent">Input events</option>
         <option value="BasicTestApp.InteropComponent">Interop component</option>
         <option value="BasicTestApp.InteropOnInitializationComponent">Interop on initialization</option>
+        <option value="BasicTestApp.JsonSerializationCases">JSON serialization</option>
         <option value="BasicTestApp.KeyCasesComponent">Key cases</option>
         <option value="BasicTestApp.KeyPressEventComponent">Key press event</option>
         <option value="BasicTestApp.LaggyTypingComponent">Laggy typing</option>

src/Components/test/testassets/BasicTestApp/JsonSerializationCases.razor

@@ -0,0 +1,35 @@
+@using System.Text.Json
+@using System.Text.Json.Serialization
+
+<h3 id="json-serialization-cases">JSON serialization cases</h3>
+
+<p>
+    Most aspects of System.Text.Json don't need to be tested here, as that's an external library. However some cases
+    are worth verifying under WebAssembly/linking specifically.
+</p>
+
+<p>Name: <strong id="deserialized-name">@deserializedPerson.Name</strong></p>
+<p>Age: <strong id="deserialized-age">@deserializedPerson.Age</strong></p>
+<p>Mood: <strong id="deserialized-mood">@deserializedPerson.Mood</strong></p>
+
+@code {
+    Person deserializedPerson;
+
+    protected override void OnInitialized()
+    {
+        // Round-trip some data
+        var input = new Person { Name = "Lord Smythe", Age = 68, Mood = EmotionalState.Vexed };
+        var serializedJson = JsonSerializer.Serialize(input);
+        deserializedPerson = JsonSerializer.Deserialize<Person>(serializedJson);
+    }
+
+    public class Person
+    {
+        public string Name { get; set; }
+        public int Age { get; set; }
+        public EmotionalState Mood { get; set; }
+    }
+
+    [JsonConverter(typeof(JsonStringEnumConverter))]
+    public enum EmotionalState { Sombre, Vexed, Irate, Tormented }
+}