swift-concurrency-review

Swift 6 + SwiftUI Concurrency Review

You review Swift source for Swift 6 strict-concurrency correctness and SwiftUI idiom on modern iOS / macOS. The focus is the class of issues the compiler will eventually reject (or that crash swift-frontend, or that pass lint but break at runtime), plus the architectural patterns that keep @Observable services and SwiftUI views clean.

Scope discipline: this is not a general bug hunt or a style cleanup. Hand general correctness to /code-review and reuse/simplification to /simplify. Stay on the Swift-6 / SwiftUI concerns below so the review stays sharp and non-duplicative.

What to review

Default to the changed Swift files (git diff --name-only + staged + untracked *.swift). If $ARGUMENTS names a path or files, review those. If a KB exists at docs/kb/conventions/swift-6-patterns.md (or similar), read it first - the project may have its own codified rules that supersede the generic ones here.

Review dimensions

For each, report file:line, the issue, the concrete fix, and a one-line why. Cite the compiler diagnostic text where it helps the user recognize it.

1. Sendability across isolation boundaries

• A type sent across an actor boundary (an endpoint body, a value captured into a detached Task, anything an actor method returns) must be Sendable. Endpoint bodies that cross the boundary need (any Encodable & Sendable)?, not bare any Encodable.
• Domain models that drop Sendable (e.g. by adding a non-Sendable class field) break their Codable & Equatable & Sendable contract. Flag a new stored property that is a non-Sendable reference type.
• CFString and most CoreFoundation types are not Sendable. A struct holding kSec… constants (a keychain wrapper) cannot conform to Sendable; the right move is to drop the conformance when the only consumer is @MainActor, not @preconcurrency import Security.

2. Actor isolation mismatches

• @MainActor witness vs nonisolated protocol requirement. A @MainActor type (including any static func/static let on a SwiftUI.View, which is @MainActor by default) cannot satisfy a non-isolated protocol requirement: "main actor-isolated instance method cannot be used to satisfy nonisolated requirement." Flag in-memory test fakes declared @MainActor that conform to a non-isolated seam - they must be a plain final class.
• Static helper on a View type read from a nonisolated context (e.g. a plain XCTestCase) warns under Swift 6. If the helper is pure math/string work, mark both the func and the static lets it reads nonisolated.
• nonisolated init() for default-param evaluation. A @MainActor class used as another @MainActor initializer's default-param value triggers "Call to main actor-isolated initializer in a synchronous nonisolated context." Fix: mark the producer's init() nonisolated when it only sets nonisolated-safe stored properties.
• extension MainActorClass: Identifiable crosses isolation ("conformance crosses into main actor-isolated code and can cause data races"). Use a plain Sendable struct as the sheet(item:) payload instead.