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 let`s 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. ### 3. Banned legacy patterns (project rules on modern stacks) - `import Combine`, `ObservableObject`, `@Published` - replace with `@Observable` + `@State`/`@Environment`. Flag any reintroduction. - `DispatchQueue.main.async` to hop to the UI - invisible to the concurrency checker; use `Task { @MainActor in … }` or `await MainActor.run`. - `@unchecked Sendable`, `nonisolated(unsafe)`, `MainActor.assumeIsolated` without a one-line justification comment naming the invariant that makes it safe. These are escape hatches, not defaults. ### 4. Force-unwraps and unsafe boundaries - `URL(string: "…")!` and other force-unwraps (SwiftLint `force_unwrapping`). Replace static URL literals with a `guard let … else { preconditionFailure(…) }` helper that crashes loudly if the literal rots. - `try!` on `ModelContainer(...)` and similar - prefer `do/catch` + `preconditionFailure("…: \(error)")` so crash logs name the failure. - Boundary input (`[String: Any]`, raw JSON) leaking past the networking layer instead of being decoded into typed models immediately. ### 5. SwiftData `#Predicate` macro limits - `#Predicate` rejects `Optional<Date>` nil-coalescing combined with other clauses ("cannot convert … to closure result type 'any StandardPredicateExpression<Bool>'"). Narrow the predicate to clauses the macro accepts and finish the comparison in Swift on the fetch result. - `#Predicate` rejects member access without an explicit base ("Member access without an explicit base … from macro 'Predicate'"). Write `Date.distantFuture`, not `.distantFuture`. - Upserts that insert `Cached.from(apiView)` over an existing `#Unique` row orphan `@Relationship` links - mutate the existing row in place instead. - A "never touch unread/starred" protection rule must be encoded **in** the predicate, not implied by the primary AND-chain, or protected rows get deleted when the implication does not hold. ### 6. Toolchain crash hazards - **`Binding(get: instanceMethod, set: instanceMethod)` referencing `@MainActor` methods** crashes `swift-frontend` on Swift 6.3.x (`report_fatal_error` in `SyncCallEmission::setArgs`). Lint passes; only `xcodebuild` shows it. Fix: closure literals `Binding(get: { … }, set: { newValue in … })`. ### 7. Cross-platform SwiftUI guards - iOS-only view modifiers on a file that also compiles for macOS must be wrapped in `#if os(iOS)` at the smallest scope: `.keyboardType`, `.textInputAutocapitalization`, `.navigationBarTitleDisplayMode`, `.tabViewBottomAccessory`. (`.textContentType`, `.autocorrectionDisabled`, `.scrollDismissesKeyboard` are cross-platform - do not over-guard.) - `.windowResizability(.contentMinSize)` does nothing without a paired `.frame(minWidth:minHeight:)`, both under `#if os(macOS)`. - `import UIKit` on a cross-platform file belongs inside `#if os(iOS)`. ### 8. SwiftUI architecture - Views importing from sibling views; views doing I/O or orchestrating other views (views should be leaves consuming injected state and emitting intents). - Hardcoded colors/hex in views instead of theme tokens via `@Environment`. - `@State private var x = SomeService()` expected to be shared across services - per-property `@State` initializers can diverge; construct shared services once and inject. ## Output ``` Swift 6 / SwiftUI Review — 4 files App/Services/AuthService.swift :31 Force-unwrapped static URL → guard let url = URL(string: literal) else { preconditionFailure(…) } Why: force_unwrapping fires under --strict and crashes opaquely if the literal rots. :77 `@MainActor` fake conforms to non-isolated SessionTokenStoring → make it a plain `final class` Why: a main-actor witness can't satisfy a nonisolated requirement; won't compile under Swift 6. App/Views/ReaderView.swift :120 `.keyboardType(.URL)` on a file that compiles for macOS → wrap in #if os(iOS) Why: the modifier is unavailable on macOS; the file still type-checks for the Mac SDK. Clean: App/Models/Article.swift, App/App.swift Summary: 3 findings across 2 files. Run /swift-verify to confirm against the compiler. ``` This is a report-only review. Do not edit files. Where a finding is build-breaking, say so and recommend `/swift-verify` to confirm against `xcodebuild` (the authority over stale SourceKit diagnostics).