[6.0] [Macro] Compiler error when producing extension macro with `@preconcurrency` attribute

[soumyamahunt]

Description

If an extension macro produces an extension that declares conformance to a protocol with @preconcurrency attribute. The compiler gives error:

'preconcurrency' attribute only applies in inheritance clauses

But inlining the macro expansion, code is compiled without any error.

For example let's suppose @Codable is an extension macro that produces Decodable conformance to actor, i.e.

@Codable
actor SomeActorCodable {
    @CodedIn("deeply", "nested1")
    let value1: String
    @CodedIn("deeply", "nested2")
    var value2: String?
    @CodedIn("deeply", "nested3")
    var value3: String!
}

produces an extension declaration

extension SomeActorCodable: @preconcurrency Decodable {
}

Compiler shows following error for produced expansion:

Showing All Messages /var/folders/r6/gctp971x7bgg0sgxjqy8z7s00000gq/T/swift-generated-sources/@__swiftmacro16MetaCodableTests09SomeActorB00B0fMe.swift:1:29: 'preconcurrency' attribute only applies in inheritance clauses

Reproduction

1. Add MetaCodable swift package: https://github.com/SwiftyLab/MetaCodable targeting branch swift-testing.

2. Add an actor declaration with @Codable macro attached, i.e.

   @Codable
   actor SomeActorCodable {
       @CodedIn("deeply", "nested1")
       let value1: String
       @CodedIn("deeply", "nested2")
       var value2: String?
       @CodedIn("deeply", "nested3")
       var value3: String!
   }

3. See the error when macro expanded during compile/build.

Expected behavior

Macro expansion should be accepted.

Environment

swift-driver version: 1.115 Apple Swift version 6.0 (swiftlang-6.0.0.9.10 clang-1600.0.26.2) Target: x86_64-apple-macosx14.0

Additional information

No response