swiftlang/swift

global actor annotations can be applied to inheritance clauses

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#86,693 创建于 2026年1月21日

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 (2 评论) (0 反应) (0 负责人)Swift (69,989 star) (10,719 fork)batch import
accepts invalidactor isolationattributesconcurrencygood first issueinheritance clausesswift 6.3type checker

描述

Description

This code is, as far as I understand, meaningless. It should not be accepted, even though I think it is just a no-op. I bet it is now parsed because of isolated conformances but then just silently dropped further down the line.

Reproduction

class Base {
}

class Derived: @MainActor Base {
}

Expected behavior

This should produce an error.

Environment

Apple Swift version 6.3-dev (LLVM d402ab9729f318e, Swift 2de856568572fc0) Target: arm64-apple-macosx26.0

Additional information

No response

贡献者指南

技术栈
swift
领域
backend
议题类型
bug
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
4
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
1-3 hours
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
active
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
understanding of Swift concurrencyknowledge of compiler parsing
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
30
研究方向
Investigate the Swift compiler's parsing of inheritance clauses, specifically how global actor annotations like @MainActor are applied. The issue suggests the annotation is parsed but then silently dropped. Look at the parser code for class declarations (e.g., in lib/Parse/ParseDecl.cpp) and the semantic analysis (e.g., in lib/Sema/TypeCheckDecl.cpp) to see where the error should be emitted. Add a diagnostic to reject such meaningless annotations.