[jeremydmiller]

Fixes #1087

Problem

For an Apply-only event on an aggregate that does not exist yet, the source generator built the aggregate as new T { Required = default!, ... } whenever it had required members. That overwrote initializers like public required List<string> Emails { get; set; } = []; with null, so Apply threw. Marten 8 ran the constructor, so initializers ran. A catch-all Create(object) intended to take control of that case made every Apply-fallback arm unreachable instead (CS8120, an error inside generated code).

Fix

BuildAggregateConstructorExpression:

Aggregate	Before	Now
public parameterless ctor, no required	new T()	new T()
public ctor marked [SetsRequiredMembers]	new T { X = default!, … }	new T()
public ctor, required members	new T { X = default!, … }	(T)Activator.CreateInstance(typeof(T))!
no public parameterless ctor	GetUninitializedObject	unchanged

required is compile-time only, so Activator.CreateInstance runs the constructor and every initializer, as Marten 8 did; with a typeof literal it stays trim/AOT safe. Only paid on the first event for a missing aggregate.

Null-snapshot switch: Apply-fallback arms already matched by an earlier Create for a base type or interface are no longer emitted. Fixes CS8120 for Create(object) and for an interface Create(IDocEvent) + Apply(Renamed) where Renamed : IDocEvent. The Create wins, as in Marten 8, so Create(object _) => null ignores events for documents that don't exist.

Behaviour change: an Apply-only event on a missing aggregate now sees initializer values where it used to see null.

Not in scope (follow-up): Create(IEvent) recognition, and a constructor taking the event as a creation on the projection path.

Tests

• RequiredMemberConstructionTests (generator): 4 tests, all failing on the old generator
• Bug_1087_required_members_on_missing_aggregate (EventTests, real generated evolver): initializers survive, Create(object) => null yields no snapshot, Apply still runs on an existing aggregate; the file does not compile on the old generator
• Generator tests 105/105; EventTests 1646/1646 on net9.0 and net10.0

🤖 Generated with Claude Code

[jeremydmiller]

Merged main, which brought in #1088's fix for the same regression. #1088 copies a required member's initializer into the object initializer when that initializer can be copied safely. This PR builds the aggregate with Activator.CreateInstance(typeof(T)), which runs the constructor and every initializer. That also covers members set with Guid.NewGuid(), with a constant of the aggregate or in the constructor body, so #1088's RequiredMemberValue / IsSelfContained helpers were no longer used and have been removed.

#1088's 13-member fixture is kept in RequiredMemberInitializerTests. Its two tests that checked the generated text now check that the aggregate is built through its constructor, and its nullable-enabled compile test passes unchanged. A new runtime test in EventTests (Bug_1087_required_members_on_missing_aggregate) checks that a Guid.NewGuid() initializer, a constant and a constructor-body assignment survive building a missing aggregate. Against #1088's emitter, that test fails with Token == Guid.Empty.

Thanks to Kenneth Skovhede for #1088 and for that fixture.

🤖 Generated with Claude Code