Fix V4 Apple Pay button customization API (#321)

## What?

Ports the relevant Apple Pay customization fix from the legacy V3 checkout sheet kit into the V4 Swift SDK.

- Replaces the V4 Apple Pay customization API with PassKit-native modifiers:
  - `.applePayButtonType(_:)`
  - `.applePayButtonStyle(_:)`
- Stores and passes `PKPaymentButtonType` / `PKPaymentButtonStyle` directly through the Apple Pay button stack.
- Removes the V3-only SwiftUI wrapper conversion path from V4.
- Includes the Apple Pay button type in the SwiftUI identity so dynamic type changes recreate the underlying `PKPaymentButton`.
- Updates Swift samples, README usage, and the Swift API baseline.

## Why?

The V3 patch needed backwards-compatible shims for deprecated Apple Pay customization APIs. V4 does not need that compatibility layer, so this keeps only the V4-relevant fix: using native PassKit values directly and ensuring the button identity reflects both style and type.

## Validation

- [x] `shadowenv exec -- env CURRENT_SIMULATOR_UUID=E8D7913B-0229-4D36-9B22-455726BEDA9E /opt/dev/bin/dev swift test ApplePayButtonCustomizationTests`
- [x] `shadowenv exec -- /opt/dev/bin/dev swift api check`
- [x] `shadowenv exec -- /opt/dev/bin/dev swift lint`
- [x] `shadowenv exec -- env CURRENT_SIMULATOR_UUID=E8D7913B-0229-4D36-9B22-455726BEDA9E /opt/dev/bin/dev swift test`
- [x] `shadowenv exec -- env CURRENT_SIMULATOR_UUID=E8D7913B-0229-4D36-9B22-455726BEDA9E /opt/dev/bin/dev swift build packages`
- [x] Branch-built iOS sample smoke with `agent-device`: built and installed `CheckoutKitSwiftDemo.app`, opened first product, verified enabled/hittable `Buy with Apple Pay` button rendered.

Smoke screenshot saved locally at `/tmp/checkout-kit-agent-device/v4-checkoutkit-demo-apple-pay-product.png`.

Author: kieran-osgood-shopify

platforms/swift/README.md

@@ -392,8 +392,8 @@ import ShopifyAcceleratedCheckouts
 
 AcceleratedCheckoutButtons(cartID: cartID)
   .wallets([.shopPay, .applePay])
-  .applePayLabel(.buy)
-  .applePayStyle(.automatic)
+  .applePayButtonType(.buy)
+  .applePayButtonStyle(.automatic)
   .cornerRadius(8)
   .onRenderStateChange { state in
     // loading, rendered, or error(reason:)

platforms/swift/Samples/CheckoutKitSwiftDemo/CheckoutKitSwiftDemo/Sources/Scenes/Cart/CartView.swift

@@ -41,7 +41,7 @@ struct CartView: View {
                     if let cartID = cartManager.cart?.id {
                         if #available(iOS 16, *) {
                             AcceleratedCheckoutButtons(cartID: cartID)
-                                .applePayStyle(applePayStyle.style)
+                                .applePayButtonStyle(applePayStyle.style)
                                 .onFail { error in
                                     print("[AcceleratedCheckout] Failed: \(error)")
                                 }

platforms/swift/Samples/CheckoutKitSwiftDemo/CheckoutKitSwiftDemo/Sources/Scenes/ProductView.swift

@@ -116,7 +116,7 @@ struct ProductView: View {
                             if #available(iOS 16, *) {
                                 AcceleratedCheckoutButtons(variantID: variant.id, quantity: 1)
                                     .wallets([.applePay])
-                                    .applePayStyle(applePayStyle.style)
+                                    .applePayButtonStyle(applePayStyle.style)
                                     .onFail { error in
                                         print("[AcceleratedCheckout] Failed: \(error)")
                                     }

platforms/swift/Samples/CheckoutKitSwiftDemo/CheckoutKitSwiftDemo/Sources/Scenes/SettingsView.swift

@@ -328,7 +328,7 @@ enum ApplePayStyleOption: String, CaseIterable {
     }
 
     @available(iOS 16.0, *)
-    var style: PayWithApplePayButtonStyle {
+    var style: PKPaymentButtonStyle {
         switch self {
         case .automatic: return .automatic
         case .black: return .black

platforms/swift/Samples/ShopifyAcceleratedCheckoutsApp/ShopifyAcceleratedCheckoutsApp/Views/Components/ButtonSet.swift

@@ -19,7 +19,7 @@ struct ButtonSet: View {
                     renderState: $cartRenderState
                 ) {
                     AcceleratedCheckoutButtons(cartID: cartID)
-                        .applePayLabel(.plain)
+                        .applePayButtonType(.plain)
                         .onFail { error in
                             print("❌ Checkout failed: \(error)")
                         }
@@ -43,8 +43,8 @@ struct ButtonSet: View {
                         variantID: productVariant.id,
                         quantity: firstVariantQuantity
                     )
-                    .applePayStyle(.whiteOutline)
-                    .applePayLabel(.buy)
+                    .applePayButtonStyle(.whiteOutline)
+                    .applePayButtonType(.buy)
                     .cornerRadius(24)
                     .wallets([.applePay, .shopPay])
                     .onFail { error in

platforms/swift/Sources/ShopifyAcceleratedCheckouts/Wallets/AcceleratedCheckoutButtons.swift

@@ -26,9 +26,9 @@ public struct AcceleratedCheckoutButtons: View {
     var cornerRadius: CGFloat?
     var clientContainer: CheckoutProtocolClientContainer = .init()
 
-    /// The Apple Pay button label style
-    private var applePayLabel: PayWithApplePayButtonLabel = .plain
-    private var applePayStyle: PayWithApplePayButtonStyle = .automatic
+    /// The Apple Pay button type
+    private var applePayButtonType: PKPaymentButtonType = .plain
+    private var applePayButtonStyle: PKPaymentButtonStyle = .automatic
 
     @State private var shopSettings: ShopSettings?
     @State private var currentRenderState: RenderState = .loading {
@@ -37,10 +37,9 @@ public struct AcceleratedCheckoutButtons: View {
         }
     }
 
-    /// Initializes an Apple Pay button with a cart ID
+    /// Initializes accelerated checkout buttons with a cart ID
     /// - Parameters:
     ///   - cartID: The cart ID to checkout (must start with gid://shopify/Cart/)
-    ///   - label: The label to display on the Apple Pay button
     public init(cartID: String) {
         identifier = .cart(cartID: cartID).parse()
         if case let .invariant(reason) = identifier {
@@ -49,11 +48,10 @@ public struct AcceleratedCheckoutButtons: View {
         }
     }
 
-    /// Initializes an Apple Pay button with a variant ID
+    /// Initializes accelerated checkout buttons with a variant ID
     /// - Parameters:
     ///  - variantID: The variant ID to checkout (must start with gid://shopify/ProductVariant/)
     ///  - quantity: The quantity of the variant to checkout
-    ///  - label: The label to display on the Apple Pay button
     public init(variantID: String, quantity: Int) {
         identifier = .variant(variantID: variantID, quantity: quantity).parse()
         if case let .invariant(reason) = identifier {
@@ -73,10 +71,10 @@ public struct AcceleratedCheckoutButtons: View {
                                 identifier: identifier,
                                 eventHandlers: eventHandlers,
                                 cornerRadius: cornerRadius,
-                                style: applePayStyle,
+                                buttonType: applePayButtonType,
+                                buttonStyle: applePayButtonStyle,
                                 client: clientContainer.client
                             )
-                            .label(applePayLabel)
                         case .shopPay:
                             ShopPayButton(
                                 identifier: identifier,
@@ -127,15 +125,15 @@ public struct AcceleratedCheckoutButtons: View {
 
 @available(iOS 16.0, *)
 extension AcceleratedCheckoutButtons {
-    public func applePayStyle(_ color: PayWithApplePayButtonStyle) -> AcceleratedCheckoutButtons {
+    public func applePayButtonType(_ type: PKPaymentButtonType) -> AcceleratedCheckoutButtons {
         var view = self
-        view.applePayStyle = color
+        view.applePayButtonType = type
         return view
     }
 
-    public func applePayLabel(_ label: PayWithApplePayButtonLabel) -> AcceleratedCheckoutButtons {
+    public func applePayButtonStyle(_ style: PKPaymentButtonStyle) -> AcceleratedCheckoutButtons {
         var view = self
-        view.applePayLabel = label
+        view.applePayButtonStyle = style
         return view
     }
 

platforms/swift/Sources/ShopifyAcceleratedCheckouts/Wallets/ApplePay/ApplePayButton.swift

@@ -23,11 +23,11 @@ struct ApplePayButton: View {
     /// The event handlers for checkout events
     private let eventHandlers: EventHandlers
 
-    /// The Apple Pay button label style
-    private var label: PayWithApplePayButtonLabel = .plain
+    /// The Apple Pay button type
+    private let buttonType: PKPaymentButtonType
 
     /// The Apple Pay button style
-    private var style: PayWithApplePayButtonStyle = .automatic
+    private let buttonStyle: PKPaymentButtonStyle
 
     /// The corner radius for the button
     private let cornerRadius: CGFloat?
@@ -38,13 +38,15 @@ struct ApplePayButton: View {
         identifier: CheckoutIdentifier,
         eventHandlers: EventHandlers = EventHandlers(),
         cornerRadius: CGFloat?,
-        style: PayWithApplePayButtonStyle = .automatic,
+        buttonType: PKPaymentButtonType = .plain,
+        buttonStyle: PKPaymentButtonStyle = .automatic,
         client: (any CheckoutCommunicationProtocol)? = nil
     ) {
         self.identifier = identifier.parse()
         self.eventHandlers = eventHandlers
         self.cornerRadius = cornerRadius
-        self.style = style
+        self.buttonType = buttonType
+        self.buttonStyle = buttonStyle
         clientContainer = CheckoutProtocolClientContainer(client)
     }
 
@@ -55,8 +57,8 @@ struct ApplePayButton: View {
         default:
             Internal_ApplePayButton(
                 identifier: identifier,
-                label: label,
-                style: style,
+                buttonType: buttonType,
+                buttonStyle: buttonStyle,
                 configuration: ApplePayConfigurationWrapper(
                     common: resolvedConfiguration,
                     applePay: resolvedApplePayConfiguration,
@@ -82,18 +84,6 @@ struct ApplePayButton: View {
         }
         return applePayConfiguration
     }
-
-    func applePayStyle(_ style: PayWithApplePayButtonStyle) -> some View {
-        var view = self
-        view.style = style
-        return view
-    }
-
-    func label(_ label: PayWithApplePayButtonLabel) -> some View {
-        var view = self
-        view.label = label
-        return view
-    }
 }
 
 /// A view that displays an Apple Pay button for checkout
@@ -102,16 +92,20 @@ struct ApplePayButton: View {
 @available(macOS, unavailable)
 @MainActor
 struct Internal_ApplePayButton: View {
-    private let label: PayWithApplePayButtonLabel
-    private let style: PayWithApplePayButtonStyle
+    private let buttonType: PKPaymentButtonType
+    private let buttonStyle: PKPaymentButtonStyle
     private let controller: ApplePayViewController
     private let cornerRadius: CGFloat?
     @Environment(\.colorScheme) private var colorScheme
 
+    func buttonIdentity(colorScheme: ColorScheme) -> String {
+        return "\(colorScheme)-\(buttonType.rawValue)-\(buttonStyle.rawValue)"
+    }
+
     init(
         identifier: CheckoutIdentifier,
-        label: PayWithApplePayButtonLabel,
-        style: PayWithApplePayButtonStyle,
+        buttonType: PKPaymentButtonType,
+        buttonStyle: PKPaymentButtonStyle,
         configuration: ApplePayConfigurationWrapper,
         eventHandlers: EventHandlers = EventHandlers(),
         cornerRadius: CGFloat?,
@@ -122,8 +116,8 @@ struct Internal_ApplePayButton: View {
             configuration: configuration,
             client: client
         )
-        self.label = label
-        self.style = style
+        self.buttonType = buttonType
+        self.buttonStyle = buttonStyle
         self.cornerRadius = cornerRadius
         controller.onCheckoutFail = eventHandlers.checkoutDidFail
         controller.onCheckoutCancel = eventHandlers.checkoutDidCancel
@@ -132,54 +126,15 @@ struct Internal_ApplePayButton: View {
     var body: some View {
         if PKPaymentAuthorizationController.canMakePayments() {
             ApplePayButtonRepresentable(
-                buttonType: label.pkPaymentButtonType,
-                buttonStyle: style.pkPaymentButtonStyle,
+                buttonType: buttonType,
+                buttonStyle: buttonStyle,
                 cornerRadius: cornerRadius ?? 8,
                 action: { Task { @MainActor in await controller.onPress() } }
             )
-            .id("\(colorScheme)-\(style.pkPaymentButtonStyle.rawValue)")
+            .id(buttonIdentity(colorScheme: colorScheme))
             .frame(height: 48)
         } else {
             Text("errors.applePay.unsupported".localizedString)
         }
     }
 }
-
-// MARK: - Type Conversions
-
-@available(iOS 16.0, *)
-extension PayWithApplePayButtonStyle {
-    var pkPaymentButtonStyle: PKPaymentButtonStyle {
-        switch self {
-        case .black: .black
-        case .white: .white
-        case .whiteOutline: .whiteOutline
-        case .automatic: .automatic
-        default: .automatic
-        }
-    }
-}
-
-@available(iOS 16.0, *)
-extension PayWithApplePayButtonLabel {
-    var pkPaymentButtonType: PKPaymentButtonType {
-        switch self {
-        case .buy: .buy
-        case .setUp: .setUp
-        case .inStore: .inStore
-        case .donate: .donate
-        case .checkout: .checkout
-        case .book: .book
-        case .subscribe: .subscribe
-        case .reload: .reload
-        case .addMoney: .addMoney
-        case .topUp: .topUp
-        case .order: .order
-        case .rent: .rent
-        case .support: .support
-        case .contribute: .contribute
-        case .tip: .tip
-        default: .plain
-        }
-    }
-}

platforms/swift/Tests/ShopifyAcceleratedCheckoutsTests/Wallets/ApplePay/ApplePayButtonCustomizationTests.swift

@@ -0,0 +1,111 @@
+import PassKit
+@testable import ShopifyAcceleratedCheckouts
+import SwiftUI
+import XCTest
+
+@available(iOS 16.0, *)
+@MainActor
+final class ApplePayButtonCustomizationTests: XCTestCase {
+    func test_applePayButtonType_withPassKitButtonTypeModifier_shouldStorePassKitButtonType() {
+        let view = AcceleratedCheckoutButtons(cartID: "gid://Shopify/Cart/test-cart-id")
+            .applePayButtonType(.buy)
+
+        XCTAssertEqual(storedApplePayButtonType(in: view)?.rawValue, PKPaymentButtonType.buy.rawValue)
+    }
+
+    func test_applePayButtonStyle_withPassKitButtonStyleModifier_shouldStorePassKitButtonStyle() {
+        let view = AcceleratedCheckoutButtons(cartID: "gid://Shopify/Cart/test-cart-id")
+            .applePayButtonStyle(.black)
+
+        XCTAssertEqual(storedApplePayButtonStyle(in: view)?.rawValue, PKPaymentButtonStyle.black.rawValue)
+    }
+
+    func test_applePayButton_withPassKitValues_shouldPassValuesToInternalButton() {
+        let button = ApplePayButton(
+            identifier: .cart(cartID: "gid://Shopify/Cart/test-cart-id"),
+            cornerRadius: nil,
+            buttonType: .buy,
+            buttonStyle: .whiteOutline
+        )
+
+        XCTAssertEqual(storedButtonType(in: button)?.rawValue, PKPaymentButtonType.buy.rawValue)
+        XCTAssertEqual(storedButtonStyle(in: button)?.rawValue, PKPaymentButtonStyle.whiteOutline.rawValue)
+    }
+
+    func test_internalApplePayButton_withPassKitValues_shouldStoreValuesDirectly() {
+        let button = Internal_ApplePayButton(
+            identifier: .cart(cartID: "gid://Shopify/Cart/test-cart-id"),
+            buttonType: .buy,
+            buttonStyle: .whiteOutline,
+            configuration: .testConfiguration,
+            cornerRadius: nil
+        )
+
+        XCTAssertEqual(storedButtonType(in: button)?.rawValue, PKPaymentButtonType.buy.rawValue)
+        XCTAssertEqual(storedButtonStyle(in: button)?.rawValue, PKPaymentButtonStyle.whiteOutline.rawValue)
+    }
+
+    func test_applePayButtonRepresentable_withPassKitValues_shouldStoreValuesDirectly() {
+        let representable = ApplePayButtonRepresentable(
+            buttonType: PKPaymentButtonType.buy,
+            buttonStyle: PKPaymentButtonStyle.whiteOutline,
+            cornerRadius: 8,
+            action: {}
+        )
+
+        XCTAssertEqual(storedRepresentableButtonType(in: representable)?.rawValue, PKPaymentButtonType.buy.rawValue)
+        XCTAssertEqual(storedRepresentableButtonStyle(in: representable)?.rawValue, PKPaymentButtonStyle.whiteOutline.rawValue)
+    }
+
+    func test_buttonIdentity_withDifferentButtonTypes_shouldChangeIdentity() {
+        let plainButton = Internal_ApplePayButton(
+            identifier: .cart(cartID: "gid://Shopify/Cart/test-cart-id"),
+            buttonType: .plain,
+            buttonStyle: .automatic,
+            configuration: .testConfiguration,
+            cornerRadius: nil
+        )
+        let buyButton = Internal_ApplePayButton(
+            identifier: .cart(cartID: "gid://Shopify/Cart/test-cart-id"),
+            buttonType: .buy,
+            buttonStyle: .automatic,
+            configuration: .testConfiguration,
+            cornerRadius: nil
+        )
+
+        XCTAssertNotEqual(
+            plainButton.buttonIdentity(colorScheme: .light),
+            buyButton.buttonIdentity(colorScheme: .light)
+        )
+    }
+
+    private func storedApplePayButtonType(in view: AcceleratedCheckoutButtons) -> PKPaymentButtonType? {
+        return childValue(named: "applePayButtonType", in: view)
+    }
+
+    private func storedApplePayButtonStyle(in view: AcceleratedCheckoutButtons) -> PKPaymentButtonStyle? {
+        return childValue(named: "applePayButtonStyle", in: view)
+    }
+
+    private func storedButtonType(in value: some Any) -> PKPaymentButtonType? {
+        return childValue(named: "buttonType", in: value)
+    }
+
+    private func storedButtonStyle(in value: some Any) -> PKPaymentButtonStyle? {
+        return childValue(named: "buttonStyle", in: value)
+    }
+
+    private func storedRepresentableButtonType(in value: some Any) -> PKPaymentButtonType? {
+        return childValue(named: "buttonType", in: value)
+    }
+
+    private func storedRepresentableButtonStyle(in value: some Any) -> PKPaymentButtonStyle? {
+        return childValue(named: "buttonStyle", in: value)
+    }
+
+    private func childValue<Value>(named name: String, in value: some Any) -> Value? {
+        return Mirror(reflecting: value).children.first { child in
+            child.label == name
+        }?.value as? Value
+    }
+}