swiftlang/swift

Error says `@preconcurrency` only applies in inheritance clauses

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#88,338 建立於 2026年4月7日

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@preconcurrencyTypeResolverattributescompilergood first issueswift 6.3type checker

描述

Description

This is not true. The attribute can also be used on declarations such as types, functions, and imports.

Reproduction

let _: @preconcurrency @MainActor() -> Void = {}

error: '@preconcurrency' only applies in inheritance clauses
  83 | 
  84 | let _: @preconcurrency @MainActor() -> Void = {}
     |        `- error: '@preconcurrency' only applies in inheritance clauses
  85 |

Expected behavior

An accurate error message. It might be better to say that @preconcurrency cannot be used on a type attribute instead of enumerating all the valid positions.

Environment

Swift version 6.3-dev (fefcb257b5b5d32)

Additional information

No response

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技術棧
swift
領域
developer experience
議題類型
bug
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
2
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1-3 hours
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fresh
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clear
前置要求
無
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
70
研究方向
Search the Swift compiler source code for the exact error message 'only applies in inheritance clauses' to locate the diagnostic. The message is likely in a diagnostics file (e.g., DiagnosticsFrontend.def). Once found, modify the string to state that @preconcurrency cannot be used on a type attribute, as suggested in the issue. Ensure the fix is consistent with other diagnostic messages. Then update any existing test cases that reference the old error message to expect the new one.