/swift-concurrency-expert

name: swift-concurrency-expert
description: "Swift concurrency review/fix: compiler errors, Sendable, isolation, remediation."

Swift Concurrency Expert

_Attribution: copied from @Dimillian’s `Dimillian/Skills` (2025-12-31)._

Overview

Review and fix Swift Concurrency issues in Swift 6.2+ codebases by applying actor isolation, Sendable safety, and modern concurrency patterns with minimal behavior changes.

Workflow

1. Triage the issue

• Capture the exact compiler diagnostics and the offending symbol(s).
• Identify the current actor context (`@MainActor`, `actor`, `nonisolated`) and whether a default actor isolation mode is enabled.
• Confirm whether the code is UI-bound or intended to run off the main actor.

2. Apply the smallest safe fix

Prefer edits that preserve existing behavior while satisfying data-race safety.

Common fixes:

• **UI-bound types**: annotate the type or relevant members with `@MainActor`.
• **Protocol conformance on main actor types**: make the conformance isolated (e.g., `extension Foo: @MainActor SomeProtocol`).
• **Global/static state**: protect with `@MainActor` or move into an actor.
• **Background work**: move expensive work into a `@concurrent` async function on a `nonisolated` type or use an `actor` to guard mutable state.
• **Sendable errors**: prefer immutable/value types; add `Sendable` conformance only when correct; avoid `@unchecked Sendable` unless you can prove thread safety.

Reference material

• See `references/swift-6-2-concurrency.md` for Swift 6.2 changes, patterns, and examples.
• See `references/swiftui-concurrency-tour-wwdc.md` for SwiftUI-specific concurrency guidance.