8000 [6.0] [Macro] Compiler error when producing extension macro with `@preconcurrency` attribute · Issue #76745 · swiftlang/swift · GitHub
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[6.0] [Macro] Compiler error when producing extension macro with @preconcurrency attribute #76745

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soumyamahunt opened this issue Sep 27, 2024 · 3 comments
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[6.0] [Macro] Compiler error when producing extension macro with @preconcurrency attribute #76745

soumyamahunt opened this issue Sep 27, 2024 · 3 comments
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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. swift macro Feature → declarations: Swift `macro` declarations

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@soumyamahunt
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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/@_swiftmacro_16MetaCodableTests09SomeActorB00B0fMe.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
@soumyamahunt soumyamahunt added bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. triage needed This issue needs more specific labels labels Sep 27, 2024
@jacbro2021
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@soumyamahunt Were you able to find a work around for this issue? I am having the same problem when creating an extension macro that adds @unchecked Sendable.

@ahoppen ahoppen added swift macro Feature → declarations: Swift `macro` declarations and removed triage needed This issue needs more specific labels labels Apr 23, 2025
@ahoppen
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ahoppen commented Apr 23, 2025

Reduced the issue to the following sample macro.

Test.zip

@DougGregor
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This is fixed for Swift 6.2, via #81249

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bug A deviation from expected or documented behavior. Also: expected but undesirable behavior. swift macro Feature → declarations: Swift `macro` declarations
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@DougGregor @ahoppen @soumyamahunt @jacbro2021
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