Improve Native AOT Support (Closes #1085)

[fdcastel]

Based on #1089. Closes #1085.

This PR implements four of the seven suggestions from #1085 to improve YamlDotNet's Native AOT support via StaticDeserializerBuilder and the YamlDotNet.Analyzers.StaticGenerator source generator.

Changes

1. Better Error Messages for Unregistered Types (Suggestion #5)

Files changed: StaticObjectFactoryFile.cs, ObjectTests.cs

Replaced ArgumentOutOfRangeException with InvalidOperationException in the generated StaticObjectFactory code. The new error message clearly says:

Type 'MyNamespace.MyType' is not registered in the YamlDotNet static context. Add [YamlSerializable(typeof(MyType))] to your static context class.

This replaces the ambiguous "Unknown type: ..." message thrown as ArgumentOutOfRangeException, which was misleading and hard to diagnose.

2. Support required Members in Generated Object Factories (Suggestion #2)

Files changed: StaticObjectFactoryFile.cs, ObjectTests.cs

The source generator now detects C# required properties and fields (C# 11+) and emits object initializer syntax with default! values instead of bare new T(). This prevents CS9035 compile errors when types have required members.

Before (fails):

if (type == typeof(MyType)) return new MyType();

After (works):

if (type == typeof(MyType)) return new MyType() { Name = default!, Value = default! };

3. Support OrderedDictionary<TKey, TValue> in the Static Context (Suggestion #3)

Files changed: SerializableSyntaxReceiver.cs

Added recognition of System.Collections.Generic.OrderedDictionary<TKey, TValue> (.NET 9+) in the source generator's CheckForSupportedGeneric method. The type is now correctly identified as a dictionary, enabling proper code generation for IsDictionary, GetKeyType, GetValueType, and Create methods.

4. Built-in Type Converters for TimeSpan and Uri (Suggestion #4)

Files changed: TimeSpanConverter.cs (new), UriConverter.cs (new), BuilderSkeleton.cs, StaticBuilderSkeleton.cs, SerializerBuilder.cs, StaticSerializerBuilder.cs

Added TimeSpanConverter and UriConverter as built-in IYamlTypeConverter implementations, registered by default in both the regular and static builder skeletons. Both converters support JSON-compatible mode (double-quoted output).

Skipped Suggestions

The following suggestions were intentionally deferred:

• 1. Publish Source Generator NuGet Package: Packaging/release concern, not a code change.
• 6. Roslyn Analyzer for Missing Type Registrations: High-effort analyzer work requiring separate design.
• 7. Document StaticDeserializerBuilder API Parity Gaps: Documentation-only task.

Testing

• All existing tests pass (28 static generator tests on net8.0, 27 on net6.0).
• New tests added:
  • UnregisteredTypeThrowsDescriptiveException — verifies the improved error message
  • RequiredMembersWork — verifies required property round-trip (net8.0 only)
  • TimeSpanConverterTests (9 tests) — unit + round-trip tests
  • UriConverterTests (8 tests) — unit + round-trip tests
• Full solution builds successfully across all target frameworks (net8.0, net6.0, net47, netstandard2.0, netstandard2.1).

Pre-existing Test Failures

4 tests in UnquotedStringTypeDeserialization_RegularNumbers fail due to floating-point precision/locale issues unrelated to this PR. These failures also occur on master.

[fdcastel]

Added: Nullable type support for all built-in type converters

The latest commit (f6eba0e) extends all built-in converters to handle nullable types.

Problem

The converters introduced in this PR (TimeSpanConverter, UriConverter) and other pre-existing ones (GuidConverter, DateTimeConverter, DateTime8601Converter, DateTimeOffsetConverter, DateOnlyConverter, TimeOnlyConverter) only handled the base type — not the nullable counterpart. For example, TimeSpanConverter.Accepts(typeof(TimeSpan?)) returned false, so TimeSpan? properties were not handled by the converter at all.

Changes

All value-type converters (Guid, TimeSpan, DateTime, DateTimeOffset, DateOnly, TimeOnly):

• Accepts() now returns true for Nullable<T> in addition to T
• ReadYaml() returns null when the scalar value is null or empty (following the same string.IsNullOrEmpty pattern from PR Fix NullReferenceException when serializing null System.Type properties #1091)
• WriteYaml() emits an empty scalar for null values instead of throwing NullReferenceException

Reference-type converter (Uri):

• ReadYaml() and WriteYaml() now handle null values (same pattern — Accepts() didn't need changes since Uri is already nullable by nature)

SystemTypeConverter is intentionally excluded — already fixed by PR #1091.

Tests

Added NullableTypeConverterTests.cs with 18 tests covering:

• Accepts() returns true for each Nullable<T> type
• Round-trip (serialize → deserialize) for nullable properties with a value
• Round-trip for nullable properties with null

All existing tests continue to pass.

[fdcastel]

Updated PR — New features added

This PR is now rebased on top of feature/add-net9-net10-targets (#1089) to take advantage of the .NET 9/10 target framework support.

Summary of changes

1. Improve error messages for unregistered types in static context

Clear, actionable error messages when a type is missing from the static context, instead of cryptic ArgumentOutOfRangeException.

2. Support required members in generated object factories

The source generator now correctly handles C# 11 required properties/fields in [YamlSerializable] types.

3. Support OrderedDictionary<TKey, TValue> in the static context

The static generator recognizes OrderedDictionary<TKey, TValue> (introduced in .NET 9) as a dictionary type, generating correct factory, accessor, and type inspector code.

4. Built-in type converters for TimeSpan and Uri

New TimeSpanConverter and UriConverter that handle serialization/deserialization with proper formatting control, similar to the existing DateTimeConverter.

5. Handle nullable types in all built-in type converters

All built-in converters (DateTimeConverter, DateTimeOffsetConverter, GuidConverter, TimeSpanConverter, UriConverter, DateOnlyConverter, TimeOnlyConverter) now correctly accept and unwrap Nullable<T> during deserialization instead of throwing.

6. IParsable<T> support in ScalarNodeDeserializer

Types with a static Parse(string, IFormatProvider) method — including all IParsable<T> implementations (.NET 7+) — are now automatically deserialized from YAML scalars without needing a custom IYamlTypeConverter. This is especially important for the static/AOT deserialization path where the NullTypeConverter cannot perform type conversions.

7. Roslyn diagnostic YDNG001 for unregistered types

The source generator now emits a compile-time warning when a property or field on a [YamlSerializable] type references a type that is not registered in the static context. The diagnostic checks types recursively, handles nullable types, skips well-known BCL primitives, and walks generic collection type arguments.

Test results

All tests pass on net8.0, net9.0, and net10.0 (1890 passing; the 4 locale-dependent UnquotedStringTypeDeserialization_RegularNumbers failures are pre-existing on master).

[fdcastel]

I’m keeping all the changes in this PR for now, but feel free to suggest any modifications or ask me to split them into smaller PRs.

[EdwardCooke]

I merged in your other branches and now this one has conflicts. If you can get to them quickly I can merge them in in a few hours. Otherwise I'll probably create a branch from this PR and fix them in my repository and close this PR

[EdwardCooke]

Oh yeah, if you can remove net9.0 and net6.0 since those frameworks are EOL now that would be great.

[fdcastel]

I merged in your other branches and now this one has conflicts. If you can get to them quickly I can merge them in in a few hours. Otherwise I'll probably create a branch from this PR and fix them in my repository and close this PR

Working on it... 👍🏻

[fdcastel]

Merged latest master into this branch to resolve conflicts.

Conflict Summary

5 files had conflicts, all in YamlDotNet/Serialization/Converters/ — caused by the ScalarConverterBase<T> extraction from PR #1090 overlapping with the nullable type handling added in this PR.

Conflicting files:

• DateOnlyConverter.cs
• DateTime8601Converter.cs
• DateTimeConverter.cs
• DateTimeOffsetConverter.cs
• TimeOnlyConverter.cs

Resolution

Instead of keeping per-converter Accepts() overrides for nullable support, I moved the nullable type check into ScalarConverterBase<T>.Accepts():

public bool Accepts(Type type)
{
    return type == typeof(T) || Nullable.GetUnderlyingType(type) == typeof(T);
}

This gives all converters inheriting from ScalarConverterBase<T> automatic nullable type support without method hiding.

For ReadYaml and WriteYaml, the resolution combines both sides:

• Uses ConsumeScalarValue(parser) helper from master's refactoring
• Keeps the null/empty value checks needed for nullable type support
• Keeps the null guard in WriteYaml (emitting empty scalar for null values)

Verification

• Build succeeds across all 7 target frameworks (0 warnings, 0 errors)
• All 201 converter tests pass
• All 31 static generator tests pass

[fdcastel]

Oh yeah, if you can remove net9.0 and net6.0 since those frameworks are EOL now that would be great.

Doing...

[fdcastel]

Done — removed net9.0 and net6.0 from all projects (commit 45f94da).

Files updated:

• YamlDotNet/YamlDotNet.csproj: net10.0;net8.0;netstandard2.0;netstandard2.1;net47
• YamlDotNet.Test/YamlDotNet.Test.csproj: net10.0;net8.0;net47
• YamlDotNet.Fsharp.Test/YamlDotNet.Fsharp.Test.fsproj: net8.0;net47
• appveyor.yml: removed Release-Net60 and Release-Net90 artifact entries
• Dockerfile / Dockerfile.NonEnglish: removed net6.0 build and test steps

All 1972 tests pass on net8.0.