Upgrade to fully modern stack: Xcode 16 / Swift 6 / iOS 17 / @Observable / Swift Testing

[timfallmk]

Context

The current branch (claude/modernize-legacy-repo-9Z7pQ) targets Xcode 14 / Swift 5.7 / iOS 16 because that was the newest Xcode available at time of writing. This issue tracks the remaining steps to reach the fully modern baseline: Xcode 16+ / Swift 6 / iOS 17+.

All changes are mechanical — no architectural work required. The code is already written correctly; this is mostly about unlocking native language features that were held back by the Xcode 14 constraint.

---

1. Bump Xcode and SDK versions

File: WikiMessage.xcodeproj/project.pbxproj

Setting	Current	Target
IPHONEOS_DEPLOYMENT_TARGET	16.0	17.0
SWIFT_VERSION	5.7	6.0
SWIFT_STRICT_CONCURRENCY	targeted	complete
LastUpgradeCheck	1400	1700 (or current)
LastSwiftUpdateCheck	1400	1700 (or current)
objectVersion	56	77 (or current Xcode value)
compatibilityVersion	"Xcode 14.0"	"Xcode 14.0" ← keep; this is the minimum Xcode to open the project, not the build Xcode

Make all of these changes to all four XCBuildConfiguration blocks (Debug/Release for each target) and the two test target configs.

---

2. Replace ObservableObject with @Observable

@Observable (the Observation framework, iOS 17+) is cleaner than ObservableObject + @Published: no @Published boilerplate, no @StateObject/@EnvironmentObject distinction, and strict concurrency works correctly out of the box.

AppModel.swift

// Before
import Combine
import Messages

final class AppModel: ObservableObject {
    @Published var presentationStyle: MSMessagesAppPresentationStyle = .compact
    @Published var composer: (any MessageComposer)?
    @Published var selectedArticleURL: URL?
}

// After
import Observation
import Messages

@Observable
final class AppModel {
    var presentationStyle: MSMessagesAppPresentationStyle = .compact
    var composer: (any MessageComposer)?
    var selectedArticleURL: URL?
}

SearchModel.swift

// Before
import Combine
final class SearchModel: ObservableObject {
    @Published var query: String = ""
    @Published private(set) var phase: SearchPhase = .idle
    @Published private(set) var recentSearches: [String] = RecentSearchesStore.load()
    ...
}

// After
import Observation
@Observable
final class SearchModel {
    var query: String = ""
    private(set) var phase: SearchPhase = .idle
    private(set) var recentSearches: [String] = RecentSearchesStore.load()
    ...
}

NetworkMonitor.swift

// Before
import Combine
import Network
final class NetworkMonitor: ObservableObject, @unchecked Sendable {
    @Published private(set) var isConnected: Bool = true
    ...
}

// After
import Network
import Observation
@Observable
final class NetworkMonitor: @unchecked Sendable {
    private(set) var isConnected: Bool = true
    ...
}

---

3. Update SwiftUI injection patterns

With @Observable, the environment and state APIs change:

RootView.swift

// Before
@StateObject private var searchModel = SearchModel()
@EnvironmentObject private var appModel: AppModel
// injected via: .environmentObject(searchModel)

// After
@State private var searchModel = SearchModel()
@Environment(AppModel.self) private var appModel
// injected via: .environment(searchModel)

SearchResultsList.swift

// Before
@EnvironmentObject private var searchModel: SearchModel
@EnvironmentObject private var appModel: AppModel

// After
@Environment(SearchModel.self) private var searchModel
@Environment(AppModel.self) private var appModel

MessagesViewController.swift

// Before
let root = RootView().environmentObject(appModel)

// After
let root = RootView().environment(appModel)

---

4. Restore ContentUnavailableView

ContentUnavailableView is iOS 17+ and was replaced with hand-rolled VStack views. Restore the native API:

LoadingView.swift

var body: some View {
    ContentUnavailableView {
        ProgressView().controlSize(.large)
    } description: {
        Text("Searching…").foregroundStyle(.secondary)
    }
}

EmptyResultsView.swift

var body: some View {
    ContentUnavailableView.search(text: query)
}

ErrorView.swift

var body: some View {
    ContentUnavailableView {
        Label("Something went wrong", systemImage: "exclamationmark.triangle")
    } description: {
        Text(error.localizedDescription)
    } actions: {
        Button("Try Again", action: retry).buttonStyle(.bordered)
    }
}

The idle state in SearchResultsList.swift can similarly be replaced:

case .idle:
    ContentUnavailableView(
        "Search Wikipedia",
        systemImage: "magnifyingglass",
        description: Text("Type to search for articles.")
    )

---

5. Switch tests to Swift Testing

Swift Testing (@Suite, @Test, #expect) is built into Xcode 16+ and is the modern replacement for XCTestCase. All four test files need updating.

Pattern (apply to all four files)

// Before (XCTest)
import XCTest
@testable import WikiMessage_MessagesExtension

final class SummaryDTOTests: XCTestCase {
    func testDecodesTitle() throws {
        let dto = try decoder.decode(SummaryDTO.self, from: fixture())
        XCTAssertEqual(dto.title, "Albert_Einstein")
        XCTAssertEqual(dto.displayTitle, "Albert Einstein")
    }
}

// After (Swift Testing)
import Testing
import Foundation
@testable import WikiMessage_MessagesExtension

@Suite("SummaryDTO decoding")
struct SummaryDTOTests {
    @Test func decodesTitle() throws {
        let dto = try decoder.decode(SummaryDTO.self, from: fixture())
        #expect(dto.title == "Albert_Einstein")
        #expect(dto.displayTitle == "Albert Einstein")
    }
}

XCTAssertEqual(a, b) → #expect(a == b)
XCTAssertTrue(x) → #expect(x)
XCTAssertNil(x) → #expect(x == nil)
XCTAssertNotNil(x) → #expect(x != nil)
XCTFail("msg") → Issue.record("msg")
XCTAssertThrowsError → await #expect(throws: SomeError.self) { ... }

Also update WikipediaServiceTests to use #expect(throws:) for the error propagation test:

@Test func propagatesHTTPErrors() async throws {
    MockURLProtocol.handler = { _ in MockURLProtocol.response(statusCode: 404, data: Data(), url: ...) }
    await #expect(throws: HTTPClient.HTTPError.self) {
        _ = try await makeService().search(query: "anything")
    }
}

---

6. Update CI

File: .github/workflows/ci.yml

# Before
runs-on: macos-13
xcode-version: "14"
destination: "platform=iOS Simulator,name=iPhone 14,OS=latest"

# After
runs-on: macos-latest
xcode-version: latest-stable
destination: "platform=iOS Simulator,name=iPhone 16,OS=latest"

---

7. Notes and gotchas

• @retroactive on extension URL: @retroactive Identifiable is still valid and required in Swift 6 — no change needed.
• SWIFT_STRICT_CONCURRENCY = complete will surface any remaining actor-isolation warnings. Most will be in MessagesViewController (a UIViewController subclass whose lifecycle methods are implicitly @MainActor in Xcode 16 but may need explicit annotation). Expect to add a handful of @MainActor annotations.
• actor WikipediaService and actor HTTPClient are already Swift 6 correct — no changes needed there.
• MessageComposer protocol conformance (LiveMessageComposer: MessageComposer) may need @MainActor adjustments once strict concurrency is on — check the insert(_:) call site.
• The @Observable macro requires import Observation, not import Combine. Remove the Combine imports from the model files.
• Fixture JSON loading in tests: Bundle(for: type(of: self)) is an XCTestCase pattern. With Swift Testing, use Bundle.module if the tests are in a Swift package, or Bundle(for: MockURLProtocol.self) (class reference, works in both).

---

Acceptance criteria

• Project compiles clean with zero errors and zero warnings under Xcode 16+, Swift 6 strict concurrency
• All WikiMessageExtensionTests tests pass using Swift Testing
• CI passes on macos-latest with xcode-version: latest-stable
• Extension runs on an iOS 17+ simulator: search returns results, tapping a result inserts a message
• No force-unwraps or try! introduced