swiftlang/swift

`isolated` keyword incorrectly permitted in inheritance clause

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#83,538 opened on Aug 5, 2025

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 (1 comment) (0 reactions) (1 assignee)Swift (69,989 stars) (10,719 forks)batch import
accepts invalidactor isolationcompilerconcurrencygood first issueinheritance clausestype checker

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

Tech stack
swift
Domain
tooling
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.
under 1 hour
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
blocked
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Swift syntax basicsCompiler parsing conceptsSwift proposal SE 0470
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the Swift compiler's parsing of inheritance clauses in `lib/Parse`. Locate where `isolated` is accepted as a protocol conformance keyword. Check commit history for any partial removal of SE 0470 syntax. The issue may require a simple removal of a token or a case in the parser. Review the assignee's work if any.