Separate writing property names out as a new method, for compatibility

src/NodaTime.Serialization.SystemTextJson/NodaConverterBase.cs

@@ -115,16 +115,26 @@ public override void Write(Utf8JsonWriter writer, T value, JsonSerializerOptions
         /// <param name="value">The value to write.</param>
         /// <param name="options">The serializer options to use for any embedded serialization.</param>
         public override void WriteAsPropertyName(Utf8JsonWriter writer, T value, JsonSerializerOptions options) =>
-            WriteJsonImpl(writer, value, options, true);
+            WriteJsonPropertyNameImpl(writer, value, options);
 
         /// <summary>
         /// Implemented by concrete subclasses, this performs the final write operation for a non-null value of type T
         /// to JSON.
         /// </summary>
         /// <param name="writer">The writer to write JSON data to</param>
-        /// <param name="value">The value to serializer</param>
+        /// <param name="value">The value to serialize</param>
         /// <param name="options">The serializer options to use for nested serialization</param>
-        /// <param name="isProperty">Boolean flag to determine which writer method to invoke</param>
-        protected abstract void WriteJsonImpl(Utf8JsonWriter writer, T value, JsonSerializerOptions options, bool isProperty = false);
+        protected abstract void WriteJsonImpl(Utf8JsonWriter writer, T value, JsonSerializerOptions options);
+
+        /// <summary>
+        /// Implemented by concrete subclasses, this performs the final write operation for a non-null value of type T
+        /// to JSON, writing the value as a property name. The default implementation throws <see cref="NotImplementedException"/>
+        /// for compatibility purposes, but all concrete classes within this package override and implement the method fully.
+        /// </summary>
+        /// <param name="writer">The writer to write JSON data to</param>
+        /// <param name="value">The value to serialize</param>
+        /// <param name="options">The serializer options to use for nested serialization</param>
+        protected virtual void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, T value, JsonSerializerOptions options) =>
+            throw new NotImplementedException();
     }
 }

src/NodaTime.Serialization.SystemTextJson/NodaDateIntervalConverter.cs

@@ -73,8 +73,7 @@ protected override DateInterval ReadJsonImpl(ref Utf8JsonReader reader, JsonSeri
         /// <param name="writer">The writer to write JSON to</param>
         /// <param name="value">The date interval to serialize</param>
         /// <param name="options">The serializer options for embedded serialization.</param>
-        /// <param name="isProperty">DateInterval cannot be converted to a scalar string value as such it is not a valid choice for a dictionary key</param>
-        protected override void WriteJsonImpl(Utf8JsonWriter writer, DateInterval value, JsonSerializerOptions options, bool isProperty = false)
+        protected override void WriteJsonImpl(Utf8JsonWriter writer, DateInterval value, JsonSerializerOptions options)
         {
             writer.WriteStartObject();
 
@@ -88,5 +87,15 @@ protected override void WriteJsonImpl(Utf8JsonWriter writer, DateInterval value,
 
             writer.WriteEndObject();
         }
+
+        /// <summary>
+        /// Unconditionally throws an exception, as a DateInterval cannot be serialized as a JSON property name.
+        /// </summary>
+        /// <param name="writer">The writer to write JSON to</param>
+        /// <param name="value">The date interval to serialize</param>
+        /// <param name="options">The serializer options for embedded serialization.</param>
+        /// <exception cref="InvalidOperationException">Always thrown to indicate this is not an appropriate method to call on this type.</exception>
+        protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, DateInterval value, JsonSerializerOptions options) =>
+            throw new JsonException("Cannot serialize a DateInterval as a JSON property name using this converter");
     }
 }

src/NodaTime.Serialization.SystemTextJson/NodaDateTimeZoneConverter.cs

@@ -41,14 +41,16 @@ protected override DateTimeZone ReadJsonImpl(ref Utf8JsonReader reader, JsonSeri
         /// <param name="writer">The writer to write JSON data to.</param>
         /// <param name="value">The value to serialize.</param>
         /// <param name="options">The serialization options to use for nested serialization.</param>
-        /// <param name="isProperty">Conditional to indicate which function to invoke on the writer</param>
-        protected override void WriteJsonImpl(Utf8JsonWriter writer, DateTimeZone value, JsonSerializerOptions options,
-            bool isProperty = false)
-        {
-            if (isProperty) 
-                writer.WritePropertyName(value.Id);
-            else
-                writer.WriteStringValue(value.Id);
-        }
+        protected override void WriteJsonImpl(Utf8JsonWriter writer, DateTimeZone value, JsonSerializerOptions options) =>
+            writer.WriteStringValue(value.Id);
+
+        /// <summary>
+        /// Writes the time zone ID to the writer as a property name
+        /// </summary>
+        /// <param name="writer">The writer to write JSON data to.</param>
+        /// <param name="value">The value to serialize.</param>
+        /// <param name="options">The serialization options to use for nested serialization.</param>
+        protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, DateTimeZone value, JsonSerializerOptions options) =>
+            writer.WritePropertyName(value.Id);
     }
 }

src/NodaTime.Serialization.SystemTextJson/NodaIntervalConverter.cs

@@ -64,8 +64,7 @@ protected override Interval ReadJsonImpl(ref Utf8JsonReader reader, JsonSerializ
         /// <param name="writer">The writer to write JSON to</param>
         /// <param name="value">The interval to serialize</param>
         /// <param name="options">The serializer options for embedded serialization.</param>
-        /// <param name="isProperty">Interval cannot be converted to a scalar string value as such it is not a valid choice for a dictionary key</param>
-        protected override void WriteJsonImpl(Utf8JsonWriter writer, Interval value, JsonSerializerOptions options, bool isProperty = false)
+        protected override void WriteJsonImpl(Utf8JsonWriter writer, Interval value, JsonSerializerOptions options)
         {
             writer.WriteStartObject();
 
@@ -83,5 +82,15 @@ protected override void WriteJsonImpl(Utf8JsonWriter writer, Interval value, Jso
             }
             writer.WriteEndObject();
         }
+
+        /// <summary>
+        /// Unconditionally throws an exception, as an Interval cannot be serialized as a JSON property name.
+        /// </summary>
+        /// <param name="writer">The writer to write JSON to</param>
+        /// <param name="value">The date interval to serialize</param>
+        /// <param name="options">The serializer options for embedded serialization.</param>
+        /// <exception cref="InvalidOperationException">Always thrown to indicate this is not an appropriate method to call on this type.</exception>
+        protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, Interval value, JsonSerializerOptions options) =>
+            throw new JsonException("Cannot serialize an Interval as a JSON property name using this converter");
     }
 }

src/NodaTime.Serialization.SystemTextJson/NodaIsoDateIntervalConverter.cs

@@ -59,15 +59,18 @@ protected override DateInterval ReadJsonImpl(ref Utf8JsonReader reader, JsonSeri
         /// <param name="writer">The writer to write JSON to</param>
         /// <param name="value">The date interval to serialize</param>
         /// <param name="options">The serializer options for embedded serialization.</param>
-        /// <param name="isProperty">Conditional to indicate which function to invoke on the writer</param>
-        protected override void WriteJsonImpl(Utf8JsonWriter writer, DateInterval value, JsonSerializerOptions options, bool isProperty = false)
+        protected override void WriteJsonImpl(Utf8JsonWriter writer, DateInterval value, JsonSerializerOptions options)
         {
             var pattern = LocalDatePattern.Iso;
             var text = $"{pattern.Format(value.Start)}/{pattern.Format(value.End)}";
-            if (isProperty)
-                writer.WritePropertyName(text);
-            else
-                writer.WriteStringValue(text);
+            writer.WriteStringValue(text);
+        }
+
+        protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, DateInterval value, JsonSerializerOptions options)
+        {
+            var pattern = LocalDatePattern.Iso;
+            var text = $"{pattern.Format(value.Start)}/{pattern.Format(value.End)}";
+            writer.WritePropertyName(text);
         }
     }
 }

src/NodaTime.Serialization.SystemTextJson/NodaIsoIntervalConverter.cs

@@ -49,15 +49,18 @@ protected override Interval ReadJsonImpl(ref Utf8JsonReader reader, JsonSerializ
         /// <param name="writer">The writer to write JSON to</param>
         /// <param name="value">The interval to serialize</param>
         /// <param name="options">The serializer options for embedded serialization.</param>
-        /// <param name="isProperty">Interval cannot be converted to a scalar string value as such it is not a valid choice for a dictionary key</param>
-        protected override void WriteJsonImpl(Utf8JsonWriter writer, Interval value, JsonSerializerOptions options, bool isProperty = false)
+        protected override void WriteJsonImpl(Utf8JsonWriter writer, Interval value, JsonSerializerOptions options)
         {
             var pattern = InstantPattern.ExtendedIso;
             var text = $"{(value.HasStart ? pattern.Format(value.Start) : "")}/{(value.HasEnd ? pattern.Format(value.End) : "")}";
-            if (isProperty)
-                writer.WritePropertyName(text);
-            else
-                writer.WriteStringValue(text);
+            writer.WriteStringValue(text);
+        }
+
+        protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, Interval value, JsonSerializerOptions options)
+        {
+            var pattern = InstantPattern.ExtendedIso;
+            var text = $"{(value.HasStart ? pattern.Format(value.Start) : "")}/{(value.HasEnd ? pattern.Format(value.End) : "")}";
+            writer.WritePropertyName(text);
         }
     }
 }

src/NodaTime.Serialization.SystemTextJson/NodaPatternConverter.cs

@@ -2,9 +2,9 @@
 // Use of this source code is governed by the Apache License 2.0,
 // as found in the LICENSE.txt file.
 
+using NodaTime.Text;
 using System;
 using System.Text.Json;
-using NodaTime.Text;
 
 namespace NodaTime.Serialization.SystemTextJson
 {
@@ -61,15 +61,24 @@ protected override T ReadJsonImpl(ref Utf8JsonReader reader, JsonSerializerOptio
         /// <param name="writer">The writer to write JSON data to</param>
         /// <param name="value">The value to serialize</param>
         /// <param name="options">The serializer options to use for nested serialization</param>
-        /// <param name="isProperty">Conditional to indicate which function to invoke on the writer</param>
-        protected override void WriteJsonImpl(Utf8JsonWriter writer, T value, JsonSerializerOptions options, bool isProperty = false)
+        protected override void WriteJsonImpl(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
+        {
+            validator?.Invoke(value);
+            var text = pattern.Format(value);
+            writer.WriteStringValue(text);
+        }
+
+        /// <summary>
+        /// Writes the formatted value to the writer.
+        /// </summary>
+        /// <param name="writer">The writer to write JSON data to.</param>
+        /// <param name="value">The value to serialize.</param>
+        /// <param name="options">The serialization options to use for nested serialization.</param>
+        protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, T value, JsonSerializerOptions options)
         {
             validator?.Invoke(value);
             var text = pattern.Format(value);
-            if (isProperty)
-                writer.WritePropertyName(text);
-            else
-                writer.WriteStringValue(text);
+            writer.WritePropertyName(text);
         }
     }
 }

src/NodaTime.Serialization.Test/SystemTextJson/NodaConverterBaseTest.cs

@@ -75,10 +75,11 @@ protected override int ReadJsonImpl(ref Utf8JsonReader reader, JsonSerializerOpt
                 return int.Parse(reader.GetString());
             }
 
-            protected override void WriteJsonImpl(Utf8JsonWriter writer, int value, JsonSerializerOptions options, bool isProperty = false)
-            {
+            protected override void WriteJsonImpl(Utf8JsonWriter writer, int value, JsonSerializerOptions options) =>
                 writer.WriteStringValue(value.ToString());
-            }
+
+            protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, int value, JsonSerializerOptions options) =>
+                writer.WritePropertyName(value.ToString());
         }
 
         private class TestStringConverter : NodaConverterBase<string>
@@ -88,10 +89,11 @@ protected override string ReadJsonImpl(ref Utf8JsonReader reader, JsonSerializer
                 return reader.GetString();
             }
 
-            protected override void WriteJsonImpl(Utf8JsonWriter writer, string value, JsonSerializerOptions options, bool isProperty = false)
-            {
+            protected override void WriteJsonImpl(Utf8JsonWriter writer, string value, JsonSerializerOptions options) =>
                 writer.WriteStringValue(value);
-            }
+
+            protected override void WriteJsonPropertyNameImpl(Utf8JsonWriter writer, string value, JsonSerializerOptions options) =>
+                writer.WritePropertyName(value);
         }
     }
 }

src/NodaTime.Serialization.Test/SystemTextJson/NodaDateIntervalConverterTest.cs

@@ -4,6 +4,7 @@
 
 using NodaTime.Serialization.SystemTextJson;
 using NUnit.Framework;
+using System.Collections.Generic;
 using System.Text.Json;
 using static NodaTime.Serialization.Test.SystemText.TestHelper;
 
@@ -165,6 +166,16 @@ public void Deserialize_CaseInsensitive_CamelCase()
             Assert.AreEqual(expectedInterval, intervalCamelCase);
         }
 
+        [Test]
+        public void CannotUseDateIntervalAsPropertyName()
+        {
+            var obj = new Dictionary<DateInterval, string>
+            {
+                {  new DateInterval(new LocalDate(2012, 1, 2), new LocalDate(2013, 6, 7)), "Test" }
+            };
+            Assert.Throws<JsonException>(() => JsonSerializer.Serialize(obj, options));
+        }
+
         public class TestObject
         {
             public DateInterval Interval { get; set; }

src/NodaTime.Serialization.Test/SystemTextJson/NodaIntervalConverterTest.cs

@@ -2,6 +2,7 @@
 // Use of this source code is governed by the Apache License 2.0,
 // as found in the LICENSE.txt file.
 
+using System.Collections.Generic;
 using System.Text.Json;
 using NodaTime.Serialization.SystemTextJson;
 using NUnit.Framework;
@@ -171,6 +172,16 @@ public void Deserialize_CaseInsensitive_CamelCase()
             Assert.AreEqual(expectedInterval, intervalCamelCase);
         }
 
+        [Test]
+        public void CannotUseIntervalAsPropertyName()
+        {
+            var obj = new Dictionary<Interval, string>
+            {
+                {  new Interval(NodaConstants.UnixEpoch, NodaConstants.UnixEpoch), "Test" }
+            };
+            Assert.Throws<JsonException>(() => JsonSerializer.Serialize(obj, options));
+        }
+
         public class TestObject
         {
             public Interval Interval { get; set; }