Add source generator discovery for natural key aggregates

src/JasperFx.Events.SourceGenerator/AggregateAnalyzer.cs

@@ -89,6 +89,8 @@ internal sealed class CandidateInfo
     public List<ITypeSymbol> DiscoveredPublishedTypes { get; set; } = new();
     // SelfAggregatingEvolve-specific
     public EvolveMethodInfo? EvolveMethod { get; set; }
+    // Natural key discovery
+    public bool HasNaturalKey { get; set; }
 }
 
 internal static class AggregateAnalyzer
@@ -209,7 +211,8 @@ internal static class AggregateAnalyzer
             AggregateType = classSymbol,
             IdentityType = idType,
             Methods = methods,
-            HasDefaultConstructor = HasParameterlessConstructor(classSymbol)
+            HasDefaultConstructor = HasParameterlessConstructor(classSymbol),
+            HasNaturalKey = HasNaturalKeyProperty(classSymbol)
         };
     }
 
@@ -242,7 +245,8 @@ internal static class AggregateAnalyzer
             AggregateType = classSymbol,
             IdentityType = idType,
             HasDefaultConstructor = HasParameterlessConstructor(classSymbol),
-            EvolveMethod = evolveMethod
+            EvolveMethod = evolveMethod,
+            HasNaturalKey = HasNaturalKeyProperty(classSymbol)
         };
     }
 
@@ -1069,6 +1073,17 @@ private static bool HasParameterlessConstructor(INamedTypeSymbol type)
         return constructors.Any(c => c.Parameters.Length == 0 && c.DeclaredAccessibility == Accessibility.Public);
     }
 
+    /// <summary>
+    /// Checks if the type has a property marked with [NaturalKey] attribute
+    /// </summary>
+    private static bool HasNaturalKeyProperty(INamedTypeSymbol type)
+    {
+        return type.GetMembers()
+            .OfType<IPropertySymbol>()
+            .Any(p => p.GetAttributes()
+                .Any(a => a.AttributeClass?.Name is "NaturalKeyAttribute" or "NaturalKey"));
+    }
+
     /// <summary>
     /// Checks if the type has an explicitly declared parameterless constructor (not implicit).
     /// Used to avoid generating a duplicate constructor in partial classes.

src/JasperFx.Events.SourceGenerator/EvolverCodeEmitter.cs

@@ -406,6 +406,10 @@ public static string EmitSelfAggregatingEvolver(CandidateInfo info)
 
         // Assembly attributes must precede namespace declarations
         sb.AppendLine($"[assembly: global::JasperFx.Events.Aggregation.GeneratedEvolver(typeof({aggregateFullName}), typeof({GetFullyQualifiedEvolverName(info, evolverName)}))]");
+        if (info.HasNaturalKey)
+        {
+            sb.AppendLine($"[assembly: global::JasperFx.Events.Aggregation.NaturalKeyAggregate(typeof({aggregateFullName}))]");
+        }
         sb.AppendLine();
 
         var ns = info.ClassSymbol.ContainingNamespace;
@@ -455,6 +459,10 @@ public static string EmitSelfAggregatingEvolveEvolver(CandidateInfo info)
 
         // Assembly attribute for discovery
         sb.AppendLine($"[assembly: global::JasperFx.Events.Aggregation.GeneratedEvolver(typeof({aggregateFullName}), typeof({GetFullyQualifiedEvolverName(info, evolverName)}))]");
+        if (info.HasNaturalKey)
+        {
+            sb.AppendLine($"[assembly: global::JasperFx.Events.Aggregation.NaturalKeyAggregate(typeof({aggregateFullName}))]");
+        }
         sb.AppendLine();
 
         var ns = info.ClassSymbol.ContainingNamespace;

src/JasperFx.Events.SourceGenerator/JasperFx.Events.SourceGenerator.csproj

@@ -12,7 +12,7 @@
         <IsRoslynComponent>true</IsRoslynComponent>
         <Description>Source generator for Fast Aggregate Projections for Marten and future JasperFx Event Stores</Description>
         <PackageId>JasperFx.Events.SourceGenerator</PackageId>
-        <Version>1.3.0</Version>
+        <Version>1.4.0</Version>
         <IncludeBuildOutput>false</IncludeBuildOutput>
         <DevelopmentDependency>true</DevelopmentDependency>
     </PropertyGroup>

src/JasperFx.Events/Aggregation/NaturalKeyAggregateAttribute.cs

@@ -0,0 +1,18 @@
+namespace JasperFx.Events.Aggregation;
+
+/// <summary>
+/// Assembly-level attribute emitted by the source generator to indicate that a self-aggregating
+/// type has a [NaturalKey] property. This allows event store implementations (e.g., Marten)
+/// to auto-register the snapshot projection and natural key infrastructure at startup,
+/// without requiring the user to explicitly call Projections.Snapshot&lt;T&gt;(Inline).
+/// </summary>
+[AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true)]
+public class NaturalKeyAggregateAttribute : Attribute
+{
+    public NaturalKeyAggregateAttribute(Type aggregateType)
+    {
+        AggregateType = aggregateType;
+    }
+
+    public Type AggregateType { get; }
+}

src/JasperFx.Events/JasperFx.Events.csproj

@@ -3,7 +3,7 @@
     <PropertyGroup>
         <Description>Foundational Event Store Abstractions and Projections for the Critter Stack</Description>
         <PackageId>JasperFx.Events</PackageId>
-        <Version>1.24.1</Version>
+        <Version>1.24.2</Version>
     </PropertyGroup>
 
     <ItemGroup>

src/JasperFx/JasperFx.csproj

@@ -3,7 +3,7 @@
         <Description>Foundational helpers and command line support used by JasperFx and the Critter Stack projects</Description>
         <AssemblyName>JasperFx</AssemblyName>
         <PackageId>JasperFx</PackageId>
-        <Version>1.21.4</Version>
+        <Version>1.21.5</Version>
     </PropertyGroup>
 
     <ItemGroup Condition="'$(TargetFramework)' == 'net8.0'">