write XNA input enums to JSON as strings automatically

Mods often reference Json.NET to do this, so this lets many mods remove Json.NET as a dependency.

release-notes.md

@@ -15,6 +15,7 @@ For mod developers:
 * Added `SaveEvents.AfterReturnToTitle` and `TimeEvents.AfterDayStarted` events.
 * Added a simpler API for console commands (see `helper.ConsoleCommands`).
 * Added `GetPrivateProperty` reflection helper.
+* SMAPI now writes XNA input enums (`Buttons` and `Keys`) to JSON as strings, so mods no longer need to add a `StringEnumConverter` themselves for those.
 * Log files now always use `\r\n` to simplify crossplatform viewing.
 * Several obsolete APIs have been removed (see [deprecation guide](http://canimod.com/guides/updating-a-smapi-mod)),
   and all _notice_-level deprecations have been increased to _info_.

src/StardewModdingAPI/Framework/Serialisation/JsonHelper.cs

@@ -1,5 +1,7 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
+using Microsoft.Xna.Framework.Input;
 using Newtonsoft.Json;
 using StardewModdingAPI.Advanced;
 
@@ -15,7 +17,11 @@ namespace StardewModdingAPI.Framework.Serialisation
         private readonly JsonSerializerSettings JsonSettings = new JsonSerializerSettings
         {
             Formatting = Formatting.Indented,
-            ObjectCreationHandling = ObjectCreationHandling.Replace // avoid issue where default ICollection<T> values are duplicated each time the config is loaded
+            ObjectCreationHandling = ObjectCreationHandling.Replace, // avoid issue where default ICollection<T> values are duplicated each time the config is loaded
+            Converters = new List<JsonConverter>
+            {
+                new SelectiveStringEnumConverter(typeof(Buttons), typeof(Keys))
+            }
         };
 
 

src/StardewModdingAPI/Framework/Serialisation/SelectiveStringEnumConverter.cs

@@ -0,0 +1,35 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Newtonsoft.Json.Converters;
+
+namespace StardewModdingAPI.Framework.Serialisation
+{
+    /// <summary>A variant of <see cref="StringEnumConverter"/> which only converts certain enums.</summary>
+    internal class SelectiveStringEnumConverter : StringEnumConverter
+    {
+        /*********
+        ** Properties
+        *********/
+        /// <summary>The enum type names to convert.</summary>
+        private readonly HashSet<string> Types;
+
+
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Construct an instance.</summary>
+        /// <param name="types">The enum types to convert.</param>
+        public SelectiveStringEnumConverter(params Type[] types)
+        {
+            this.Types = new HashSet<string>(types.Select(p => p.FullName));
+        }
+
+        /// <summary>Get whether this instance can convert the specified object type.</summary>
+        /// <param name="type">The object type.</param>
+        public override bool CanConvert(Type type)
+        {
+            return base.CanConvert(type) && this.Types.Contains(type.FullName);
+        }
+    }
+}

src/StardewModdingAPI/StardewModdingAPI.csproj

@@ -153,6 +153,7 @@
     <Compile Include="Framework\Reflection\PrivateProperty.cs" />
     <Compile Include="Framework\RequestExitDelegate.cs" />
     <Compile Include="Framework\Serialisation\JsonHelper.cs" />
+    <Compile Include="Framework\Serialisation\SelectiveStringEnumConverter.cs" />
     <Compile Include="Framework\Serialisation\SemanticVersionConverter.cs" />
     <Compile Include="ICommandHelper.cs" />
     <Compile Include="IModRegistry.cs" />