fix correctness bugs across core, JsonPath, Xml and FSharp

src/Argon.FSharp.Tests/Argon.FSharp.Tests.fsproj

@@ -9,6 +9,7 @@
 
   <ItemGroup>
     <Compile Include="FSharpListConverterTests.fs" />
+    <Compile Include="NullTokenTests.fs" />
     <PackageReference Include="FSharp.Core" />
     <PackageReference Include="xunit.v3" />
     <PackageReference Include="Microsoft.NET.Test.Sdk" />

src/Argon.FSharp.Tests/NullTokenTests.fs

@@ -0,0 +1,31 @@
+module NullTokenTests
+
+open Argon
+open Xunit
+
+type ListHolder() =
+    member val List: int list = [] with get, set
+    member val After: int = 0 with get, set
+
+type MapHolder() =
+    member val Map: Map<string, int> = Map.empty with get, set
+    member val After: int = 0 with get, set
+
+// Bug: FSharpListConverter.ReadJson had no Null handling, so a JSON null crashed and
+// desynced the reader instead of yielding a null list.
+[<Fact>]
+let ``Deserialize null into FSharp list property`` () =
+    let result =
+        JsonConvert.DeserializeObject<ListHolder>("""{"List": null, "After": 7}""", FSharpListConverter())
+
+    Assert.Null(box result.List)
+    Assert.Equal(7, result.After)
+
+// Bug: FSharpMapConverter.ReadJson had the same missing Null check.
+[<Fact>]
+let ``Deserialize null into FSharp map property`` () =
+    let result =
+        JsonConvert.DeserializeObject<MapHolder>("""{"Map": null, "After": 7}""", FSharpMapConverter())
+
+    Assert.Null(box result.Map)
+    Assert.Equal(7, result.After)

src/Argon.FSharp/FSharpListConverter.cs

@@ -21,6 +21,11 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
 
     public override object? ReadJson(JsonReader reader, Type type, object? existingValue, JsonSerializer serializer)
     {
+        if (reader.TokenType == JsonToken.Null)
+        {
+            return null;
+        }
+
         var genericArgument = type.GetGenericArguments()[0];
         return readList.MakeGenericMethod(genericArgument)
             .Invoke(

src/Argon.FSharp/FSharpMapConverter.cs

@@ -24,6 +24,11 @@ public static void WriteMap<T, K>(JsonWriter writer, FSharpMap<T, K> value, Json
 
     public override object? ReadJson(JsonReader reader, Type type, object? existingValue, JsonSerializer serializer)
     {
+        if (reader.TokenType == JsonToken.Null)
+        {
+            return null;
+        }
+
         var arguments = type.GetGenericArguments();
         return readMap.MakeGenericMethod(arguments[0], arguments[1])
             .Invoke(

src/Argon.JsonPath/FieldMultipleFilter.cs

@@ -17,8 +17,7 @@ public override IEnumerable<JToken> ExecuteFilter(JToken root, IEnumerable<JToke
                     {
                         yield return v;
                     }
-
-                    if (settings?.ErrorWhenNoMatch ?? false)
+                    else if (settings?.ErrorWhenNoMatch ?? false)
                     {
                         throw new JsonException($"Property '{name}' does not exist on JObject.");
                     }

src/Argon.JsonPath/JPath.cs

@@ -553,7 +553,7 @@ bool TryParseValue(out object? value)
             while (currentIndex < expression.Length)
             {
                 currentChar = expression[currentIndex];
-                if (currentChar is ' ' or ')')
+                if (currentChar is ' ' or ')' or '&' or '|')
                 {
                     var numberText = stringBuilder.ToString();
 

src/Argon.JsonPath/PathFilter.cs

@@ -6,7 +6,7 @@ abstract class PathFilter
     {
         if (t is JArray a)
         {
-            if (a.Count <= index)
+            if (index < 0 || a.Count <= index)
             {
                 if (settings.ErrorWhenNoMatch)
                 {

src/Argon.Xml/XmlDocumentWrapper.cs

@@ -21,7 +21,7 @@ public IXmlNode CreateXmlDeclaration(string version, string? encoding, string? s
         new XmlDeclarationWrapper(document.CreateXmlDeclaration(version, encoding, standalone));
 
     public IXmlNode CreateXmlDocumentType(string name, string? publicId, string? systemId, string? internalSubset) =>
-        new XmlDocumentTypeWrapper(document.CreateDocumentType(name, publicId, systemId, null));
+        new XmlDocumentTypeWrapper(document.CreateDocumentType(name, publicId, systemId, internalSubset));
 
     public IXmlNode CreateProcessingInstruction(string target, string data) =>
         new XmlNodeWrapper(document.CreateProcessingInstruction(target, data));

src/Argon.Xml/XmlNodeConverter.cs

@@ -295,6 +295,19 @@ void WriteGroupedNodes(JsonWriter writer, XmlNamespaceManager manager, bool writ
 
         if (writeArray)
         {
+            // Comments share the name "#comment" and cannot be array values. Write each as an
+            // inline JSON comment (which round-trips back to XML comments) instead of an empty
+            // array that silently drops the comment text.
+            if (groupedNodes[0].NodeType == XmlNodeType.Comment)
+            {
+                foreach (var node in groupedNodes)
+                {
+                    writer.WriteComment(node.Value);
+                }
+
+                return;
+            }
+
             if (writePropertyName)
             {
                 writer.WritePropertyName(elementNames);
@@ -614,16 +627,16 @@ void DeserializeValue(JsonReader reader, IXmlDocument document, XmlNamespaceMana
             switch (propertyName)
             {
                 case textName:
-                    currentNode.AppendChild(document.CreateTextNode(ConvertTokenToXmlValue(reader)!));
+                    currentNode.AppendChild(document.CreateTextNode(ConvertTokenToXmlValue(reader) ?? ""));
                     return;
                 case cDataName:
-                    currentNode.AppendChild(document.CreateCDataSection(ConvertTokenToXmlValue(reader)!));
+                    currentNode.AppendChild(document.CreateCDataSection(ConvertTokenToXmlValue(reader) ?? ""));
                     return;
                 case whitespaceName:
-                    currentNode.AppendChild(document.CreateWhitespace(ConvertTokenToXmlValue(reader)!));
+                    currentNode.AppendChild(document.CreateWhitespace(ConvertTokenToXmlValue(reader) ?? ""));
                     return;
                 case significantWhitespaceName:
-                    currentNode.AppendChild(document.CreateSignificantWhitespace(ConvertTokenToXmlValue(reader)!));
+                    currentNode.AppendChild(document.CreateSignificantWhitespace(ConvertTokenToXmlValue(reader) ?? ""));
                     return;
                 default:
                     // processing instructions and the xml declaration start with ?
@@ -874,9 +887,15 @@ void ReadArrayElements(JsonReader reader, IXmlDocument document, string property
 
         if (count == 1 && WriteArrayAttribute)
         {
+            // Match on the decoded local name and namespace (not the raw JSON property name),
+            // otherwise prefixed or XML-encoded names never match and a single-element nested
+            // array loses its json:Array marker on round-trip.
+            XmlUtils.GetQualifiedNameParts(propertyName, out var qualifiedPrefix, out var localName);
+            var ns = qualifiedPrefix.IsNullOrEmpty() ? manager.DefaultNamespace : manager.LookupNamespace(qualifiedPrefix);
+
             foreach (var childNode in nestedArrayElement.ChildNodes)
             {
-                if (childNode is IXmlElement element && element.LocalName == propertyName)
+                if (childNode is IXmlElement element && element.LocalName == localName && element.NamespaceUri == ns)
                 {
                     AddJsonArrayAttribute(element, document);
                     break;

src/Argon/JsonConvert.cs

@@ -245,8 +245,8 @@ public static string ToString(Guid value)
     public static string ToString(TimeSpan value)
     {
         Span<char> destination = stackalloc char[26];
-        value.TryFormat(destination, out _, ['c']);
-        return ToString(destination, '"');
+        value.TryFormat(destination, out var charsWritten, ['c']);
+        return ToString(destination[..charsWritten], '"');
     }
 
     /// <summary>

src/Argon/JsonConverter.cs

@@ -65,7 +65,7 @@ public sealed override void WriteJson(JsonWriter writer, object value, JsonSeria
             throw new JsonSerializationException($"Converter cannot read JSON with the specified existing value. {typeof(T)} is required.");
         }
 
-        if (reader.Value is null)
+        if (reader.TokenType is JsonToken.Null or JsonToken.Undefined)
         {
             return null;
         }

src/Argon/JsonReader.cs

@@ -1028,7 +1028,7 @@ protected void SetNoneToken()
     /// </summary>
     protected void SetUndefinedToken()
     {
-        tokenType = JsonToken.Null;
+        tokenType = JsonToken.Undefined;
         value = null;
         SetPostValueState(false);
     }

src/Argon/JsonSerializer.cs

@@ -129,12 +129,15 @@ public virtual IContractResolver? ContractResolver
 
     public JsonContract ResolveContract(Type type)
     {
-        if (contractResolver == null)
+        // Read through the virtual ContractResolver property so that subclasses
+        // (e.g. JsonSerializerProxy handed to converters) can redirect resolution.
+        var resolver = ContractResolver;
+        if (resolver == null)
         {
             return DefaultContractResolver.Instance.ResolveContract(type);
         }
 
-        return contractResolver.ResolveContract(type);
+        return resolver.ResolveContract(type);
     }
 
     /// <summary>

src/Argon/JsonTextReader.cs

@@ -2171,9 +2171,15 @@ object ParseNumberNaN(ReadType readType, bool matched)
     /// </summary>
     public override void Close()
     {
+        if (CurrentState == State.Closed)
+        {
+            return;
+        }
+
         base.Close();
 
         BufferUtils.ReturnBuffer(charBuffer);
+        charBuffer = [];
 
         if (CloseInput)
         {

src/Argon/JsonTextWriter.cs

@@ -459,7 +459,7 @@ public override void WriteValue(ushort value)
     public override void WriteValue(char value)
     {
         InternalWriteValue(JsonToken.String);
-        WriteValueInternal(JsonConvert.ToString(value));
+        WriteEscapedString([value], QuoteValue);
     }
 
     /// <summary>

src/Argon/JsonWriter.cs

@@ -796,10 +796,7 @@ public virtual void WriteValue(StringBuilder? value)
             return;
         }
 
-        foreach (var chunk in value.GetChunks())
-        {
-            WriteValue(chunk.Span);
-        }
+        WriteValue(value.ToString());
     }
 
     /// <summary>

src/Argon/Linq/JContainer.cs

@@ -402,8 +402,10 @@ internal bool TryAddInternal(int index, object? content, bool skipParentCheck)
             var multiIndex = index;
             foreach (var c in enumerable)
             {
-                TryAddInternal(multiIndex, c, skipParentCheck);
-                multiIndex++;
+                if (TryAddInternal(multiIndex, c, skipParentCheck))
+                {
+                    multiIndex++;
+                }
             }
 
             return true;

src/Argon/Linq/JObject.cs

@@ -458,7 +458,10 @@ public bool TryGetValue(string propertyName, [NotNullWhen(true)] out JToken? val
         return true;
     }
 
-    ICollection<JToken?> IDictionary<string, JToken?>.Values => throw new NotImplementedException();
+    ICollection<JToken?> IDictionary<string, JToken?>.Values =>
+        Properties()
+            .Select(_ => (JToken?) _.Value)
+            .ToList();
 
     #endregion
 

src/Argon/Linq/JValue.cs

@@ -176,13 +176,13 @@ static int CompareBigInteger(BigInteger i1, object i2)
         // check for fraction if result is two numbers are equal
         if (i2 is decimal d1)
         {
-            return 0m.CompareTo(Math.Abs(d1 - Math.Truncate(d1)));
+            return 0m.CompareTo(d1 - Math.Truncate(d1));
         }
 
         if (i2 is double or float)
         {
             var d = Convert.ToDouble(i2, InvariantCulture);
-            return 0d.CompareTo(Math.Abs(d - Math.Truncate(d)));
+            return 0d.CompareTo(d - Math.Truncate(d));
         }
 
         return result;
@@ -759,14 +759,33 @@ public override void WriteTo(JsonWriter writer, params IList<JsonConverter> conv
         throw MiscellaneousUtils.CreateArgumentOutOfRangeException(nameof(Type), valueType, "Unexpected token type.");
     }
 
-    internal override int GetDeepHashCode()
+    // Numeric JValues of the same JTokenType are equal by numeric value regardless of the
+    // backing CLR type (int vs long, decimal vs double, BigInteger). Hash a canonical double
+    // so GetHashCode stays consistent with Equals for exact numeric values. Values that are
+    // only approximately equal cannot share a hash - that is inherent to the approximate float
+    // comparison used by Equals.
+    int GetValueHashCode()
     {
-        var valueHashCode = value?.GetHashCode() ?? 0;
+        if (value == null)
+        {
+            return 0;
+        }
 
-        // GetHashCode on an enum boxes so cast to int
-        return ((int) valueType).GetHashCode() ^ valueHashCode;
+        if (valueType is JTokenType.Integer or JTokenType.Float)
+        {
+            var d = value is BigInteger bigInteger
+                ? (double) bigInteger
+                : Convert.ToDouble(value, InvariantCulture);
+            return d.GetHashCode();
+        }
+
+        return value.GetHashCode();
     }
 
+    internal override int GetDeepHashCode() =>
+        // GetHashCode on an enum boxes so cast to int
+        ((int) valueType).GetHashCode() ^ GetValueHashCode();
+
     static bool ValuesEquals(JValue v1, JValue v2) =>
         v1 == v2 || (v1.valueType == v2.valueType && Compare(v1.valueType, v1.value, v2.value) == 0);
 
@@ -804,15 +823,8 @@ public override bool Equals(object? obj)
     /// <returns>
     /// A hash code for the current <see cref="Object" />.
     /// </returns>
-    public override int GetHashCode()
-    {
-        if (value == null)
-        {
-            return 0;
-        }
-
-        return value.GetHashCode();
-    }
+    public override int GetHashCode() =>
+        GetValueHashCode();
 
     /// <summary>
     /// Returns a <see cref="String" /> that represents this instance.

src/Argon/Serialization/DefaultContractResolver.cs

@@ -37,7 +37,6 @@ public class DefaultContractResolver : IContractResolver
         new EncodingConverter(),
         new PathInfoConverter(),
         new RegexConverter(),
-        new EncodingConverter(),
         new TimeZoneInfoConverter(),
         new VersionConverter(),
         new StringWriterConverter()
@@ -690,7 +689,9 @@ protected virtual IList<JsonProperty> CreateProperties(Type type, MemberSerializ
 
         if (needsSort)
         {
-            list.Sort(static (a, b) => (a.Order ?? -1).CompareTo(b.Order ?? -1));
+            // OrderBy is a stable sort, so properties without an explicit Order keep
+            // their declaration order. List.Sort (introsort) is unstable above 16 items.
+            return list.OrderBy(_ => _.Order ?? -1).ToList();
         }
 
         return list;

src/Argon/Serialization/JsonSerializerInternalWriter.cs

@@ -912,7 +912,7 @@ static IEnumerable<DictionaryEntry> Items(IDictionary values)
         {
             if (contract.DictionaryKeyType == typeof(string))
             {
-                foreach (var entry in Items(values).OrderBy(_ => ((string) _.Key, StringComparer.OrdinalIgnoreCase)))
+                foreach (var entry in Items(values).OrderBy(_ => (string) _.Key, StringComparer.OrdinalIgnoreCase))
                 {
                     SerializeDictionaryItem(writer, contract, member, entry.Key, entry.Value, keyContract, underlying);
                 }

src/Argon/Serialization/JsonSerializerProxy.cs

@@ -67,6 +67,8 @@ public override IContractResolver? ContractResolver
         set => serializer.ContractResolver = value;
     }
 
+    public override List<JsonConverter> Converters => serializer.Converters;
+
     public override MissingMemberHandling? MissingMemberHandling
     {
         get => serializer.MissingMemberHandling;