What's New in Swift 6.3 & 6.4

import Foundation
import Testing

// 1. anyAppleOS availability — replaces listing iOS/macOS/tvOS/watchOS/visionOS separately
@available(anyAppleOS 27, *)
func fetchUserProfile(id: String) async throws -> String {
    // Simulated async fetch
    try await Task.sleep(for: .milliseconds(100))
    return "Profile(\(id))"
}

// 2. @diagnose — suppress a specific warning category in one place
// without affecting the rest of the project
struct LegacyBridge {
    @diagnose(.ignore, "deprecated_declaration")
    func callDeprecatedAPI() {
        // Imagine this calls a deprecated API — warning is silenced only here
        print("Using legacy path temporarily")
    }
}

// 3. mapKeyedValues — dictionary transform with access to both key and value
let productPrices: [String: Double] = [
    "apple": 1.20,
    "banana": 0.50,
    "cherry": 3.00
]

// Old way required constructing a new Dictionary by hand:
// var labeled: [String: String] = [:]
// for (key, value) in productPrices { labeled[key] = "\(key): $\(value)" }

// New mapKeyedValues passes both key AND value into the closure:
let labeledPrices: [String: String] = productPrices.mapKeyedValues { key, value in
    "\(key.capitalized): $\(String(format: "%.2f", value))"
}

// 4. Task cancellation shield — perform cleanup even after task is cancelled
func writeDataSafely(data: Data, to url: URL) async throws {
    let task = Task {
        // Cancel the task immediately to simulate cancellation
    }
    task.cancel()

    try await Task.withoutActuallyEscaping(data) { _ in } // illustrative

    await Task.withCancellationShield {
        // Inside here, isCancelled always returns false
        // Safe to finish writing data to avoid file corruption
        print("Completing write despite cancellation: \(data.count) bytes")
    }
}

// 5. Swift Testing — dynamic test cancellation and warning-level issues
@Suite("Product Pricing Tests")
struct PricingTests {
    @Test("Labeled prices are correctly formatted", arguments: ["apple", "banana", "cherry"])
    func testLabeledPrice(product: String) async throws {
        guard productPrices[product] != nil else {
            // Cancel just this argument instead of failing the whole suite
            try await Test.current?.cancel()
            return
        }
        let label = labeledPrices[product]!
        #expect(label.hasPrefix(product.capitalized))
    }

    @Test("Prices are positive")
    func testPositivePrices() {
        for (key, value) in productPrices {
            if value <= 0 {
                // Warning-severity issue — won't block CI
                Issue.record("\(key) has suspicious price \(value)", severity: .warning)
            }
        }
        #expect(productPrices.values.allSatisfy { $0 > 0 })
    }
}