Add legacy TypeConverter support from System.ComponentModel

This shouldn't be needed in newer ASP.NET Core since the IParsable<T>/IFormattable is the only requirement nowadays. But might be useful in other scenarios.

src/StructId.FunctionalTests/Functional.cs

@@ -24,6 +24,19 @@ public record User(UserId Id, string Name, Wallet Wallet);
 
 public class FunctionalTests(ITestOutputHelper output)
 {
+    [Fact]
+    public void TypeConverters()
+    {
+        var id = ProductId.New();
+        var converter = TypeDescriptor.GetConverter(id);
+
+        Assert.True(converter.CanConvertTo(typeof(string)));
+        Assert.True(converter.CanConvertFrom(typeof(string)));
+
+        var id2 = (ProductId?)converter.ConvertFromString(converter.ConvertToString(id)!);
+        Assert.Equal(id, id2);
+    }
+
     [Fact]
     public void JsonConversion()
     {

src/StructId.FunctionalTests/UlidTests.cs

@@ -1,4 +1,5 @@
 using System.Collections.Concurrent;
+using System.ComponentModel;
 using System.Data;
 using System.Text.Json;
 using Dapper;
@@ -69,6 +70,19 @@ public UlidToStringConverter(ConverterMappingHints? mappingHints = null)
 
 public class UlidTests
 {
+    [Fact]
+    public void TypeConverters()
+    {
+        var id = UlidId.New();
+        var converter = TypeDescriptor.GetConverter(id);
+
+        Assert.True(converter.CanConvertTo(typeof(string)));
+        Assert.True(converter.CanConvertFrom(typeof(string)));
+
+        var id2 = (UlidId?)converter.ConvertFromString(converter.ConvertToString(id)!);
+        Assert.Equal(id, id2);
+    }
+
     [Fact]
     public void JsonConversion()
     {

src/StructId/Templates/TypeConverter.cs

@@ -0,0 +1,55 @@
+// <auto-generated/>
+#nullable enable
+
+using System;
+using System.ComponentModel;
+using System.Globalization;
+using StructId;
+
+[TStructId]
+[TypeConverter(typeof(TSelf.StringConverter))]
+file readonly partial record struct TSelf(string Value)
+{
+    partial class StringConverter : TypeConverter
+    {
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
+            => sourceType == typeof(string) || sourceType == typeof(TSelf);
+
+        /// <inheritdoc />
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
+        {
+            if (value == null)
+                return default(TSelf);
+
+            if (value is string typedValue)
+                return TSelf.New(typedValue);
+
+            throw new ArgumentException($"Cannot convert '{value}' to {nameof(TSelf)}", nameof(value));
+        }
+
+        /// <inheritdoc />
+        public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destinationType) 
+            => destinationType == typeof(string) || destinationType == typeof(TSelf);
+
+        /// <inheritdoc />
+        public override object? ConvertTo(ITypeDescriptorContext? context, CultureInfo? culture, object? value, Type destinationType)
+        {
+            if (value != null)
+            {
+                if (destinationType == typeof(string))
+                    return ((TSelf)value).Value;
+
+                if (destinationType == typeof(TSelf))
+                    return value;
+            }
+
+            throw new InvalidOperationException($"Cannot convert '{value}' to '{destinationType}'");
+        }
+    }
+}
+
+file partial record struct TSelf : INewable<TSelf, string>
+{
+    public static TSelf New(string value) => throw new NotImplementedException();
+}

src/StructId/Templates/TypeConverterT.cs

@@ -0,0 +1,64 @@
+// <auto-generated/>
+#nullable enable
+
+using System;
+using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
+using System.Globalization;
+using StructId;
+
+[TStructId]
+[TypeConverter(typeof(TSelf.StringConverter))]
+file readonly partial record struct TSelf(/*!string*/ TValue Value)
+{
+    partial class StringConverter : TypeConverter
+    {
+        /// <inheritdoc />
+        public override bool CanConvertFrom(ITypeDescriptorContext? context, Type sourceType)
+            => sourceType == typeof(string) || sourceType == typeof(TSelf);
+
+        /// <inheritdoc />
+        public override object? ConvertFrom(ITypeDescriptorContext? context, CultureInfo? culture, object value)
+        {
+            if (value == null)
+                return default(TSelf);
+
+            if (value is string typedValue)
+                return TSelf.New(TValue.Parse(typedValue, culture));
+
+            throw new ArgumentException($"Cannot convert '{value}' to {nameof(TSelf)}", nameof(value));
+        }
+
+        /// <inheritdoc />
+        public override bool CanConvertTo(ITypeDescriptorContext? context, Type? destinationType) 
+            => destinationType == typeof(string) || destinationType == typeof(TSelf);
+
+        /// <inheritdoc />
+        public override object? ConvertTo(ITypeDescriptorContext? context, CultureInfo? culture, object? value, Type destinationType)
+        {
+            if (value != null)
+            {
+                if (destinationType == typeof(string))
+                    return ((TSelf)value).Value.ToString(null, culture);
+
+                if (destinationType == typeof(TSelf))
+                    return value;
+            }
+
+            throw new InvalidOperationException($"Cannot convert '{value}' to '{destinationType}'");
+        }
+    }
+}
+
+file partial record struct TSelf : INewable<TSelf, TValue>
+{
+    public static TSelf New(TValue value) => throw new NotImplementedException();
+}
+
+// This will be removed when applying the template to each user-defined struct id.
+file struct TValue : IParsable<TValue>, IFormattable
+{
+    public static TValue Parse(string s, IFormatProvider? provider) => throw new NotImplementedException();
+    public static bool TryParse([NotNullWhen(true)] string? s, IFormatProvider? provider, [MaybeNullWhen(false)] out TValue result) => throw new NotImplementedException();
+    public string ToString(string? format, IFormatProvider? formatProvider) => throw new NotImplementedException();
+}