swift-concurrency

The swift-concurrency skill helps developers review, diagnose, fix, and write concurrent Swift code for Swift 6.3 and newer. It focuses on resolving compiler diagnostics related to concurrency, including Sendable conformance issues, actor isolation violations, strict concurrency errors, and migration challenges when adopting modern Swift concurrency features. The skill emphasizes applying the smallest safe fix that preserves existing behavior while ensuring data-race safety and compliance with Swift's concurrency model.

Its capabilities include diagnosing concurrency problems through a structured triage workflow, applying actor isolation correctly, enforcing Sendable safety, and adopting modern language features such as approachable concurrency and default MainActor isolation. The skill covers key concurrency topics including structured concurrency, task cancellation, actor reentrancy, AsyncSequence and AsyncStream usage, observable types and concurrency interactions, synchronization primitives, and common concurrency mistakes. It also provides guidance for adopting features such as @MainActor isolation, @concurrent functions, nonisolated(nonsending), Task.immediate, actor-based architectures, and migration from legacy concurrency approaches to Swift 6 strict concurrency.

This skill is intended for Swift developers, application engineers, and teams modernizing codebases to Swift 6.2+ and Swift 6.3+. It is particularly useful when working on UI-bound applications, actor-based systems, asynchronous workflows, and codebases transitioning from earlier concurrency models. The skill supports both troubleshooting existing compiler errors and designing new concurrency-safe architectures that align with modern Swift best practices.