swiftlang/swift

`isolated` keyword incorrectly permitted in inheritance clause

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#83,538 opened on Aug 5, 2025

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accepts invalidactor isolationcompilerconcurrencygood first issueinheritance clausestype checker

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Description

The following compiles but shouldn't since isolated is no longer the syntax for SE-0470:

protocol P {}
struct S: isolated P {}

Contributor guide

Research direction
Investigate the parser's handling of inheritance clauses in Swift's compiler. Look for where 'isolated' is incorrectly allowed and ensure it is only permitted in specific contexts as per Swift evolution proposals.
Tech stack
swift
Domain
toolingdeveloper experience
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GitSwift
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
70