Add DateTimeSerializer

RELEASE-NOTES.md

@@ -40,6 +40,7 @@ END TEMPLATE-->
 ### New features
 
 * You can use `Subs.CVar()` from an entity systems to subscribe to CVar changes. This is more convenient than `IConfigurationManager.OnValueChanged` as it automatically unsubscribes on system shutdown.
+* There is now a built-in type serializer for `DateTime`, so you can put `DateTime`s in your data fields.
 
 ### Bugfixes
 

Robust.Shared/Serialization/TypeSerializers/Implementations/DateTimeSerializer.cs

@@ -0,0 +1,65 @@
+using System;
+using System.Globalization;
+using JetBrains.Annotations;
+using Robust.Shared.IoC;
+using Robust.Shared.Serialization.Manager;
+using Robust.Shared.Serialization.Manager.Attributes;
+using Robust.Shared.Serialization.Markdown;
+using Robust.Shared.Serialization.Markdown.Validation;
+using Robust.Shared.Serialization.Markdown.Value;
+using Robust.Shared.Serialization.TypeSerializers.Interfaces;
+
+namespace Robust.Shared.Serialization.TypeSerializers.Implementations;
+
+/// <summary>
+/// Implements serialization for <see cref="DateTime"/>.
+/// </summary>
+/// <remarks>
+/// Serialization is implemented with <see cref="DateTimeStyles.RoundtripKind"/> and the "o" format specifier.
+/// </remarks>
+[TypeSerializer]
+public sealed class DateTimeSerializer : ITypeSerializer<DateTime, ValueDataNode>, ITypeCopyCreator<DateTime>
+{
+    public ValidationNode Validate(
+        ISerializationManager serializationManager,
+        ValueDataNode node,
+        IDependencyCollection dependencies,
+        ISerializationContext? context = null)
+    {
+        return DateTime.TryParse(node.Value, null, DateTimeStyles.RoundtripKind, out _)
+            ? new ValidatedValueNode(node)
+            : new ErrorNode(node, "Failed parsing DateTime");
+    }
+
+    public DateTime Read(
+        ISerializationManager serializationManager,
+        ValueDataNode node,
+        IDependencyCollection dependencies,
+        SerializationHookContext hookCtx,
+        ISerializationContext? context = null,
+        ISerializationManager.InstantiationDelegate<DateTime>? instanceProvider = null)
+    {
+        return DateTime.Parse(node.Value, null, DateTimeStyles.RoundtripKind);
+    }
+
+    public DataNode Write(
+        ISerializationManager serializationManager,
+        DateTime value,
+        IDependencyCollection dependencies,
+        bool alwaysWrite = false,
+        ISerializationContext? context = null)
+    {
+        return new ValueDataNode(value.ToString("o"));
+    }
+
+    [MustUseReturnValue]
+    public DateTime CreateCopy(
+        ISerializationManager serializationManager,
+        DateTime source,
+        IDependencyCollection dependencies,
+        SerializationHookContext hookCtx,
+        ISerializationContext? context = null)
+    {
+        return source;
+    }
+}

Robust.UnitTesting/Shared/Serialization/TypeSerializers/DateTimeSerializerTest.cs

@@ -0,0 +1,31 @@
+using System;
+using System.Globalization;
+using NUnit.Framework;
+using Robust.Shared.Serialization.Manager;
+using Robust.Shared.Serialization.Markdown.Value;
+using Robust.Shared.Serialization.TypeSerializers.Implementations;
+
+namespace Robust.UnitTesting.Shared.Serialization.TypeSerializers;
+
+[TestFixture]
+[TestOf(typeof(DateTimeSerializer))]
+internal sealed class DateTimeSerializerTest : SerializationTest
+{
+    [Test]
+    public void WriteTest()
+    {
+        var dateTime = DateTime.UtcNow;
+        var result = Serialization.WriteValueAs<ValueDataNode>(dateTime);
+
+        var parsed = DateTime.Parse(result.Value, null, DateTimeStyles.RoundtripKind);
+        Assert.That(parsed, Is.EqualTo(dateTime));
+    }
+
+    [Test]
+    public void ReadTest()
+    {
+        var result = Serialization.Read<DateTime>(new ValueDataNode("2020-07-10 15:00:00.000"));
+
+        Assert.That(result, Is.EqualTo(new DateTime(2020, 07, 10, 15, 0, 0)));
+    }
+}