TOML

Serialize an ID

When the project references Meziantou.Framework.Toml, the generator adds a TOML converter to each ID and registers it with [TomlConverter]. It writes the value of the ID:

public sealed record OrderLine(ProductId ProductId, ProjectId ProjectId, int Quantity);

var line = new OrderLine(ProductId.FromGuid(new Guid("0f8fad5b-d9cb-469f-a165-70867728950e")), ProjectId.FromInt32(42), Quantity: 3);

var toml = Meziantou.Framework.Toml.TomlSerializer.Serialize(line);
Assert.Equal("""
    ProductId = "0f8fad5b-d9cb-469f-a165-70867728950e"
    ProjectId = 42
    Quantity = 3

    """, toml);

var deserialized = Meziantou.Framework.Toml.TomlSerializer.Deserialize<OrderLine>(toml);
Assert.Equal(line, deserialized);

How values are written

The TOML type of the value depends on the underlying type:

Underlying type	TOML value
`bool`	A boolean.
`byte`, `sbyte`, `short`, `ushort`, `int`, `uint`, `long`	An integer. Reading a value out of the range of the type throws a TomlException.
`ulong`, `Int128`, `UInt128`, `BigInteger`	An integer when the value fits in a TOML integer (a signed 64-bit integer), a string otherwise. Both are read.
`Half`, `float`, `double`	A float. Integers are read too.
`decimal`	A float with all the digits of the value. Integers are read too.
`string`, `Guid`, `ObjectId`	A string.
`DateTime`	An offset date-time with `Z` for a UTC value, with the offset of the machine for a local value, and a local date-time otherwise. A `Z` offset is read as a UTC value, another offset as a local value, and a local date-time or a local date as an unspecified value.
`DateTimeOffset`	An offset date-time. A local date-time, date or time cannot be read.

TOML has no null value. The serializer omits a property whose value is null, and the converter throws a TomlException when it is asked to write a null ID or an ID whose string value is null.

The keys of a TOML dictionary are strings: an ID cannot be the key of a dictionary.

Source generation and Native AOT

A source-generated TomlSerializerContext does not see the [TomlConverter] attribute that this generator adds to the ID: the TOML source generator cannot see the code of other source generators.

[Meziantou.Framework.Toml.Serialization.TomlSerializable(typeof(OrderLine))]
internal sealed partial class OrderTomlContext : Meziantou.Framework.Toml.Serialization.TomlSerializerContext;

Register the generated converters in options whose TypeInfoResolver is the context, and get the metadata of the type from these options:

// The generated converters are public: register them in options that use the context
var options = new Meziantou.Framework.Toml.TomlSerializerOptions
{
    TypeInfoResolver = OrderTomlContext.Default,
    Converters = [new ProductId.ProductIdTomlConverter(), new ProjectId.ProjectIdTomlConverter()],
};
var typeInfo = (Meziantou.Framework.Toml.TomlTypeInfo<OrderLine>)options.TypeInfoResolver.GetTypeInfo(typeof(OrderLine), options)!;

var line = new OrderLine(ProductId.FromGuid(new Guid("0f8fad5b-d9cb-469f-a165-70867728950e")), ProjectId.FromInt32(42), Quantity: 3);
var toml = Meziantou.Framework.Toml.TomlSerializer.Serialize(line, typeInfo);
Assert.Equal("""
    ProductId = "0f8fad5b-d9cb-469f-a165-70867728950e"
    ProjectId = 42
    Quantity = 3

    """, toml);

var deserialized = Meziantou.Framework.Toml.TomlSerializer.Deserialize(toml, typeInfo);
Assert.Equal(line, deserialized);

Add one converter per ID type that the serialized types contain.