Add ScanForTypesAttribute as dedicated attribute for custom type handling

[Copilot]

GenerateServiceRegistrationsAttribute with CustomHandler set was awkward — registration-specific properties (Lifetime, AsSelf, AsImplementedInterfaces, KeySelector) are meaningless in that context, and the attribute name itself is misleading since the handler may not register anything.

Changes

• New ScanForTypesAttribute — contains all filtering properties (AssignableTo, TypeNameFilter, AttributeFilter, etc.) and Handler, but none of the registration-specific ones
• CustomHandler on GenerateServiceRegistrationsAttribute marked [Obsolete("Use ScanForTypesAttribute instead.", error: false)] — still functional
• New diagnostics:
  • DI0013 — ScanForTypesAttribute used without Handler set
  • DI0014 — ScanForTypesAttribute and GenerateServiceRegistrationsAttribute used on the same method
• Second incremental generator provider wired up for the new attribute, sharing the existing FindServicesToRegister / source generation pipeline
• Version bumped to 3.0

Migration

// Before (deprecated)
[GenerateServiceRegistrations(AssignableTo = typeof(IEndpoint), CustomHandler = nameof(IEndpoint.MapEndpoint))]
public static partial IEndpointRouteBuilder MapEndpoints(this IEndpointRouteBuilder endpoints);

// After
[ScanForTypes(AssignableTo = typeof(IEndpoint), Handler = nameof(IEndpoint.MapEndpoint))]
public static partial IEndpointRouteBuilder MapEndpoints(this IEndpointRouteBuilder endpoints);

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Create separate attribute for custom handling</issue_title>
<issue_description>Existing GenerateServiceRegistrations attribute becomes a bit messy. When CustomHandler is specified, properties like AsSelf, Lifetime, etc become incompatible.
Also, naming GenerateServiceRegistrations becomes incorrect, as CustomHandler does not nessesary does anything regarding registrations.

We should add a separate attribute, which only applies to CustomHandler. It should contain all filtering properties, but nothing related to service registration.
Existing CustomHandler on GenerateServiceRegistrations attribute should be marked as Obsolete (but functional for now).</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes Create separate attribute for custom handling #52

---

📱 Kick off Copilot coding agent tasks wherever you are with GitHub Mobile, available on iOS and Android.

[Dreamescaper]

@copilot
Bump major version in version.json

[Copilot]

@copilot
Bump major version in version.json

Done in f138be0 — bumped version from 2.4 to 3.0.

[Dreamescaper]

@copilot
I suggest to rename GenerateServiceHandler to ScanForTypes (we'll add other functionality later, like returning found types as a collection).
Also, CustomHandler -> Handler (no point specifying that it is custom now when it is separate from registration attribute).

Let me know if you have other naming suggestions.

[Copilot]

@copilot
I suggest to rename GenerateServiceHandler to ScanForTypes (we'll add other functionality later, like returning found types as a collection).
Also, CustomHandler -> Handl...

Done in dfd4989:

• GenerateServiceHandlerAttribute → ScanForTypesAttribute
• CustomHandler property on the new attribute → Handler

The [Obsolete] on GenerateServiceRegistrationsAttribute.CustomHandler now points to ScanForTypesAttribute. The AttributeModel reads "Handler" first, then falls back to "CustomHandler" so both the new and legacy attributes work correctly.

[Dreamescaper]

@copilot
Merge lastest main and fix the build.

[Copilot]

@copilot
Merge lastest main and fix the build.

Done in 2291b64. Merged latest main (the "Use Embedded API" commit) and fixed ScanForTypesAttribute to use [Embedded] instead of [Conditional("CODE_ANALYSIS")], plus updated the three new ScanForTypes test assertions from GeneratedTrees[1] to GeneratedTrees[2] to account for the extra EmbeddedAttribute generated tree. All 82 tests pass and the Playground project builds cleanly.