Added custom deserialization for old features so that they don't totally break the load

IPA.Loader/JsonConverters/FeaturesFieldConverter.cs

@@ -0,0 +1,31 @@
+using IPA.Logging;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Linq;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace IPA.JsonConverters
+{
+    internal class FeaturesFieldConverter : JsonConverter<Dictionary<string, JObject>>
+    {
+        public override Dictionary<string, JObject> ReadJson(JsonReader reader, Type objectType, Dictionary<string, JObject> existingValue, bool hasExistingValue, JsonSerializer serializer)
+        {
+            if (reader.TokenType == JsonToken.StartArray)
+            {
+                _ = serializer.Deserialize<string[]>(reader);
+                Logger.features.Warn("Encountered old features used. They no longer do anything, please move to the new format.");
+                return existingValue;
+            }
+
+            return serializer.Deserialize<Dictionary<string, JObject>>(reader);
+        }
+
+        public override void WriteJson(JsonWriter writer, Dictionary<string, JObject> value, JsonSerializer serializer)
+        {
+            serializer.Serialize(writer, value);
+        }
+    }
+}

IPA.Loader/Loader/PluginManifest.cs

@@ -40,7 +40,7 @@ namespace IPA.Loader
         [JsonProperty("conflictsWith", Required = Required.DisallowNull, ItemConverterType = typeof(SemverRangeConverter))]
         public Dictionary<string, Range> Conflicts = new Dictionary<string, Range>();
 
-        [JsonProperty("features", Required = Required.DisallowNull)]
+        [JsonProperty("features", Required = Required.DisallowNull), JsonConverter(typeof(FeaturesFieldConverter))]
         public Dictionary<string, JObject> Features = new Dictionary<string, JObject>();
 
         [JsonProperty("loadBefore", Required = Required.DisallowNull)]