chore: add ListWithStringFallback converters and JSON roundtrip test

src/Docfx.App/Config/ListWithStringFallback.cs

@@ -6,7 +6,8 @@ namespace Docfx;
 /// <summary>
 /// ListWithStringFallback.
 /// </summary>
-[Newtonsoft.Json.JsonConverter(typeof(ListWithStringFallbackConverter))]
+[Newtonsoft.Json.JsonConverter(typeof(ListWithStringFallbackConverter.NewtonsoftJsonConverter))]
+[System.Text.Json.Serialization.JsonConverter(typeof(ListWithStringFallbackConverter.SystemTextJsonConverter))]
 internal class ListWithStringFallback : List<string>
 {
     /// <summary>

src/Docfx.App/Config/ListWithStringFallbackConverter.NewtonsoftJson.cs

@@ -0,0 +1,72 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+
+namespace Docfx;
+
+
+internal partial class ListWithStringFallbackConverter
+{
+    /// <summary>
+    /// JsonConverter for <see cref="ListWithStringFallback"/>.
+    /// </summary>
+    internal class NewtonsoftJsonConverter : JsonConverter
+    {
+        /// <inheritdoc/>
+        public override bool CanConvert(Type objectType)
+        {
+            return objectType == typeof(FileMapping);
+        }
+
+        /// <inheritdoc/>
+        public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+        {
+            var model = new ListWithStringFallback();
+            var value = reader.Value;
+            IEnumerable<JToken> jItems;
+            if (reader.TokenType == JsonToken.StartArray)
+            {
+                jItems = JArray.Load(reader);
+            }
+            else if (reader.TokenType == JsonToken.StartObject)
+            {
+                jItems = JContainer.Load(reader);
+            }
+            else if (reader.TokenType == JsonToken.String)
+            {
+                jItems = JRaw.Load(reader);
+            }
+            else
+            {
+                jItems = JObject.Load(reader);
+            }
+
+            if (jItems is JValue)
+            {
+                model.Add(jItems.ToString());
+            }
+            else
+            {
+                foreach (var item in jItems)
+                {
+                    model.Add(item.ToString());
+                }
+            }
+
+            return model;
+        }
+
+        /// <inheritdoc/>
+        public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+        {
+            writer.WriteStartArray();
+            foreach (var item in (ListWithStringFallback)value)
+            {
+                serializer.Serialize(writer, item);
+            }
+            writer.WriteEndArray();
+        }
+    }
+}

src/Docfx.App/Config/ListWithStringFallbackConverter.SystemTextJson.cs

@@ -0,0 +1,56 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using System.IO;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+using YamlDotNet.Serialization;
+
+namespace Docfx;
+
+
+internal partial class ListWithStringFallbackConverter
+{
+    /// <summary>
+    /// JsonConverter for <see cref="ListWithStringFallback"/>.
+    /// </summary>
+    internal class SystemTextJsonConverter : JsonConverter<ListWithStringFallback>
+    {
+        public override ListWithStringFallback Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            var tokenType = reader.TokenType;
+            switch (tokenType)
+            {
+                case JsonTokenType.String:
+                    {
+                        var value = reader.GetString();
+                        return new ListWithStringFallback([value]);
+                    }
+                case JsonTokenType.StartArray:
+                    {
+                        var items = JsonSerializer.Deserialize<string[]>(ref reader, options);
+                        return new ListWithStringFallback(items);
+                    }
+                case JsonTokenType.StartObject:
+                    {
+                        using var document = JsonDocument.ParseValue(ref reader);
+                        JsonElement root = document.RootElement;
+                        var values = root.EnumerateObject().Select(x=>x.ToString());
+                        return new ListWithStringFallback(values);
+                    }
+                default:
+                    throw new NotSupportedException($"TokenType({reader.TokenType}) is not supported.");
+            }
+        }
+
+        public override void Write(Utf8JsonWriter writer, ListWithStringFallback value, JsonSerializerOptions options)
+        {
+            writer.WriteStartArray();
+            foreach (var item in value)
+            {
+                writer.WriteStringValue(item);
+            }
+            writer.WriteEndArray();
+        }
+    }
+}

src/Docfx.App/Config/ListWithStringFallbackConverter.cs

@@ -6,63 +6,7 @@
 
 namespace Docfx;
 
-/// <summary>
-/// JsonConverter for <see cref="ListWithStringFallback"/>.
-/// </summary>
-internal class ListWithStringFallbackConverter : JsonConverter
-{
-    /// <inheritdoc/>
-    public override bool CanConvert(Type objectType)
-    {
-        return objectType == typeof(FileMapping);
-    }
-
-    /// <inheritdoc/>
-    public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
-    {
-        var model = new ListWithStringFallback();
-        var value = reader.Value;
-        IEnumerable<JToken> jItems;
-        if (reader.TokenType == JsonToken.StartArray)
-        {
-            jItems = JArray.Load(reader);
-        }
-        else if (reader.TokenType == JsonToken.StartObject)
-        {
-            jItems = JContainer.Load(reader);
-        }
-        else if (reader.TokenType == JsonToken.String)
-        {
-            jItems = JRaw.Load(reader);
-        }
-        else
-        {
-            jItems = JObject.Load(reader);
-        }
-
-        if (jItems is JValue)
-        {
-            model.Add(jItems.ToString());
-        }
-        else
-        {
-            foreach (var item in jItems)
-            {
-                model.Add(item.ToString());
-            }
-        }
 
-        return model;
-    }
-
-    /// <inheritdoc/>
-    public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
-    {
-        writer.WriteStartArray();
-        foreach (var item in (ListWithStringFallback)value)
-        {
-            serializer.Serialize(writer, item);
-        }
-        writer.WriteEndArray();
-    }
+internal partial class ListWithStringFallbackConverter
+{
 }

src/Docfx.Common/Json/JsonUtility.cs

@@ -99,6 +99,7 @@ private static bool IsSupported()
 
                 // Intermediate types for tests. it's expected to be removed later (And return true by default).
                 case "Docfx.FileMapping":
+                case "Docfx.ListWithStringFallback":
                 case "Docfx.Plugins.MarkdownServiceProperties":
                     return true;
 

test/docfx.Tests/SerializationTests/JsonSerializationTest.ListWithStringFallback.cs

@@ -0,0 +1,22 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+
+using Docfx;
+using Docfx.Common;
+using FluentAssertions;
+
+namespace docfx.Tests;
+
+public partial class JsonSerializationTest
+{
+    [Theory]
+    [TestData<ListWithStringFallback>]
+    public void JsonSerializationTest_ListWithStringFallback(string path)
+    {
+        // Arrange
+        var model = TestData.Load<ListWithStringFallback>(path);
+
+        // Act/Assert
+        ValidateJsonRoundTrip(model);
+    }
+}

test/docfx.Tests/SerializationTests/TestData/ListWithStringFallback/ListWithStringFallback_01.json

@@ -0,0 +1 @@
+"string_item1"

test/docfx.Tests/SerializationTests/TestData/ListWithStringFallback/ListWithStringFallback_02.json

@@ -0,0 +1,5 @@
+[
+  "array_item_01",
+  "array_item_02",
+  "array_item_03"
+]

test/docfx.Tests/SerializationTests/TestData/ListWithStringFallback/ListWithStringFallback_03.json

@@ -0,0 +1,5 @@
+{
+  "object_item_01": "1",
+  "object_item_02": "2",
+  "object_item_03": "3"
+}