Feature Detection

The unified generator doesn’t have a configuration file. Instead it asks the Roslyn compilation: “is this marker type reachable?”. If yes, the corresponding feature is activated for this build. If no, the generator stays silent — no stale code, no useless files.

This is the composition-by-presence principle in action: add a NuGet, the generator notices; remove it, the generated code disappears.

Mechanism

// Pragmatic.SourceGenerator/Core/FeatureDetector.cs (verbatim shape)
internal static class FeatureDetector
{
    public static DetectedFeatures Detect(Compilation compilation) => new()
    {
        HasActions = TypeExists(compilation, "Pragmatic.Actions.Attributes.DomainActionAttribute"),
        HasEndpoints = TypeExists(compilation, "Pragmatic.Endpoints.Attributes.EndpointAttribute"),
        HasPersistenceEFCore = TypeExists(compilation, "Pragmatic.Persistence.EFCore.PragmaticDbContextAttribute"),
        HasMessaging = TypeExists(compilation, "Pragmatic.Messaging.Attributes.MessageHandlerAttribute"),
        HasJobs = TypeExists(compilation, "Pragmatic.Jobs.Attributes.RecurringJobAttribute"),
        HasResult = TypeExists(compilation, "Pragmatic.Result.IError"),
        // … ~32 flags total + EfCoreProvider
    };

    private static bool TypeExists(Compilation compilation, string fullyQualifiedName)
        => compilation.GetTypeByMetadataName(fullyQualifiedName) is not null;
}

Detect runs once per compilation and returns an immutable DetectedFeatures record. Each flag is read by the generator pipelines to decide whether to run — e.g. JobsFeature (which is actually registered unconditionally) and MessagingFeature only emit when their marker type resolves.

Generic markers use backtick arity

Generic attributes resolve under their CLR metadata name, so MapFromAttribute<TSource> is detected as Pragmatic.Mapping.Attributes.MapFromAttribute`1 — note the `1 suffix and the .Attributes sub-namespace. Dropping either makes the lookup miss.

The flags

A representative subset of the ~32 flags. The complete, authoritative list — including the exact marker FQNs — lives in DetectedFeatures.cs and FeatureDetector.cs. FQNs below are copied verbatim from FeatureDetector.cs.

Flag	Marker type (FQN)	Module
HasActions	Pragmatic.Actions.Attributes.DomainActionAttribute	Pragmatic.Actions
HasValidation	Pragmatic.Validation.Attributes.ValidationAttribute	Pragmatic.Validation
HasCaching	Pragmatic.Caching.Attributes.CacheableAttribute	Pragmatic.Caching
HasMapping	Pragmatic.Mapping.Attributes.MapFromAttribute`1	Pragmatic.Mapping
HasEndpoints	Pragmatic.Endpoints.Attributes.EndpointAttribute	Pragmatic.Endpoints
HasPersistence	Pragmatic.Persistence.Query.Attributes.QueryAttribute`2	Pragmatic.Persistence
HasPersistenceEFCore	Pragmatic.Persistence.EFCore.PragmaticDbContextAttribute	Pragmatic.Persistence.EFCore
HasPatch	Pragmatic.Patch.Attributes.GeneratePatchAttribute`1	Pragmatic.Patch
HasComposition	(detected by CompositionDetector)	Pragmatic.Composition(.Host)
HasI18n	Pragmatic.Internationalization.Attributes.TranslationKeysAttribute	Pragmatic.Internationalization
HasResult	Pragmatic.Result.IError	Pragmatic.Result
HasConfiguration	Pragmatic.Configuration.ConfigurationAttribute	Pragmatic.Configuration
HasResilience	Pragmatic.Resilience.Attributes.ResiliencePolicyAttribute	Pragmatic.Resilience
HasIdentityAspNetCore	Pragmatic.Identity.Authorization.PragmaticPermissionRequirement	Pragmatic.Identity (ASP.NET Core)
HasIdentityPersistence	Pragmatic.Identity.Persistence.Entities.IdentityUserBase`1	Pragmatic.Identity.Persistence
HasAuthorization	Pragmatic.Authorization.PragmaticBuilderAuthorizationExtensions	Pragmatic.Authorization
HasMultiTenancy	Pragmatic.MultiTenancy.ITenantContext	Pragmatic.MultiTenancy
HasFeatureFlags	Pragmatic.FeatureFlags.FeatureFlagServiceCollectionExtensions	Pragmatic.FeatureFlags
HasDiscovery	Pragmatic.Discovery.Abstractions.IDiscoveryService	Pragmatic.Discovery
HasTemporal	Pragmatic.Temporal.Clock.SystemClock	Pragmatic.Temporal
HasEventsEFCore	Pragmatic.Events.EFCore.DomainEventsInterceptor	Pragmatic.Events.EFCore
HasMessaging	Pragmatic.Messaging.Attributes.MessageHandlerAttribute	Pragmatic.Messaging
HasMessagingEFCore	Pragmatic.Messaging.EFCore.Outbox.OutboxInterceptor	Pragmatic.Messaging.EFCore
HasMessagingChannels	Pragmatic.Messaging.Channels.ChannelTransport	Pragmatic.Messaging.Channels
HasMessagingRabbitMq	Pragmatic.Messaging.RabbitMQ.RabbitMqTransport	Pragmatic.Messaging.RabbitMQ
HasMessagingAuditing	Pragmatic.Messaging.Auditing.IAuditStore	Pragmatic.Messaging.Auditing
HasMessagingSagas	Pragmatic.Messaging.Saga.ISagaRepository`1	Pragmatic.Messaging (sagas)
HasMessagingJobs	Pragmatic.Messaging.Jobs.PublishMessageJob	Pragmatic.Messaging.Jobs
HasJobs	Pragmatic.Jobs.Attributes.RecurringJobAttribute	Pragmatic.Jobs
HasMigrations	Pragmatic.Migrations.Schema.SchemaVersion	Pragmatic.Migrations
HasComments	Pragmatic.Comments.HasCommentsAttribute	Pragmatic.Comments (Traits)
HasControlPlane	Pragmatic.ControlPlane.IControlPlane	Pragmatic.ControlPlane
HasNotifications	Pragmatic.Notifications.INotificationService	Pragmatic.Notifications
IsHostMode / IsHostCompositionMode	(entry-point + Composition.Host ref)	host detection

EF Core provider detection

Beyond the boolean flags, FeatureDetector resolves an EfCoreProvider enum so the persistence templates can emit provider-specific SQL. It probes the referenced EF Core provider assemblies in priority order:

Probe (marker type)	Result
Microsoft.EntityFrameworkCore.NpgsqlDbContextOptionsBuilderExtensions	PostgreSql
Microsoft.EntityFrameworkCore.SqlServerDbContextOptionsBuilderExtensions	SqlServer
Microsoft.EntityFrameworkCore.SqliteDbContextOptionsBuilderExtensions	Sqlite
(none of the above)	Generic

PostgreSQL wins over SQL Server, which wins over SQLite — so a project referencing more than one provider resolves to the highest-priority match.

Why a marker type instead of assembly name?

Three reasons, in order of importance:

1. Meta-packages don’t break detection. If a Pragmatic.Composition meta-package pulls in Pragmatic.Composition.Host plus Pragmatic.Actions, detection by assembly name would produce duplicate triggers. Detection by type fires exactly once per real type, independent of how you got there.
2. Renames are decoupled. If a module is ever renamed at the assembly level, the type-level marker can stay stable — detection keeps working until the real API moves.
3. Fast at compile time. GetTypeByMetadataName is one of the cheapest Roslyn lookups. No reflection walk, no assembly enumeration.

Cross-feature composition

Detection is not binary-only: when multiple features are active, they can compose. Example:

• HasActions and HasPersistenceEFCore → the Action template can emit LoadEntity invocations that go through the generated repository.
• HasMessaging and HasPersistenceEFCore → the Messaging template emits an outbox that uses the DbContext from the persistence feature.
• HasAuthorization and HasActions → the Action invoker gets a permission check filter automatically.

These cross-feature enrichers live in the top-level Compositions/ folder of the generator and run after the per-feature transforms.

Adding a detection probe

When you add a new feature:

Core/DetectedFeatures.cs

public bool HasMyFeature { get; init; }

// Core/FeatureDetector.cs — inside the Detect(...) object initializer
HasMyFeature = TypeExists(compilation, "Pragmatic.MyFeature.SomeMarkerType"),

The rest of the generator pipeline can then guard its work on detected.HasMyFeature. Tests cover the matrix of “feature absent” vs “feature present” to ensure the generator produces zero output when the module is not referenced.

Debugging detection

If a feature is unexpectedly silent:

1. Open obj/Generated/ and check whether any _Infra.*.Registration.g.cs was emitted for that feature. If missing, the flag was false.
2. Verify the project file references the module NuGet (not just a transitive via meta-package — meta-packages work too, but check the graph with dotnet list package --include-transitive).
3. Ensure the marker type name matches the current FeatureDetector.cs — types get renamed occasionally across minor versions.