[local_auth] Convert iOS/macOS to Swift #9459

stuartmorgan-g · 2025-06-20T11:57:23Z

Rewrites the iOS/macOS implementation in Swift. This is an in-place rewrite with minimal changes, to minimize the chances of breakage, and to simplify review. Future refactorings can improve the Swift structure (e.g., fully adopting thread enforcement).

flutter/flutter#119104

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stuartmorgan-g

I did this conversion manually (as a way to practice Swift); no auto-conversion or AI tools involved. I deliberately did it in-place, pretty much line by line, to simplify side-by-side review. I've left notes about changes that aren't just direct language conversion below.

stuartmorgan-g · 2025-06-20T11:58:59Z

...th/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/SystemWrappers.swift

This can mostly be compared side-by-side to FLALocalAuthPlugin_Test.h

stuartmorgan-g · 2025-06-20T11:59:43Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

This should be renamed in a follow-up; I didn't rename it here because there are enough changes that git would probably not show it as a diff, making review harder.

stuartmorgan-g · 2025-06-20T12:00:18Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

+import LocalAuthentication


This should always have been here, but transitive includes in Obj-C masked the missing include.

stuartmorgan-g · 2025-06-20T12:00:50Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

@@ -16,24 +17,24 @@ import XCTest
 private let timeout: TimeInterval = 30.0

 /// A context factory that returns preset contexts.
-final class StubAuthContextFactory: NSObject, FLADAuthContextFactory {
+final class StubAuthContextFactory: AuthContextFactory {


I removed NSObject from all the test implementations since the protocols aren't Obj-C now, so it was just cruft.

stuartmorgan-g · 2025-06-20T12:01:13Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

-  var contexts: [FLADAuthContext]
-  init(contexts: [FLADAuthContext]) {
+  var contexts: [AuthContext]
+  init(contexts: [AuthContext]) {


All the Pigeon-generated type names changed because there's no more prefixing.

stuartmorgan-g · 2025-06-20T12:18:41Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+
+/// A flutter plugin for local authentication.
+// TODO(stuartmorgan): Remove the @unchecked Sendable, and convert to strict thread enforcement.
+// This was added to minimize the changes while converting from Swift to Objective-C.


This was unfortunate, but it was the best I could come up with to fix all the warnings without significant restructuring. Without this, the places where we dispatch from a potentially-background-thread-callback back to a main thread call to a method on self triggers warnings about self not being Sendable.

There are ways to fix that with more static methods, passing more state around instead of using self, etc., but they would require refactoring that I didn't want to combine with the language conversion as it would have made side-by-side review nearly impossible.

I think let's keep @unchecked Sendable for now. I plan to look closer into Swift concurrency later this year

stuartmorgan-g · 2025-06-20T12:20:59Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+        self.handleError(authError, options: options, strings: strings, completion: completion)
+      } else {
+        // This should not happen according to docs, but if it ever does the plugin should still
+        // fire the completion.


This branch is new. In Obj-C, we just assumed the docs weren't lying about the error being set if it returned false, but that's not type safe in Swift, and since docs have lied about nullability before I wanted a fallback instead of a crash from force-unwrapping.

stuartmorgan-g · 2025-06-20T12:21:59Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+          animated: true,
+          completion: nil)
+      } else {
+        // TODO(stuartmorgan): Create a new error code for failure to show UI, and return it here.


This branch is new. We were failing to handle the case where there is no view before, so I added minimal handling for now.

stuartmorgan-g · 2025-06-20T12:22:52Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+          self.handleResult(succeeded: false, completion: completion)
+        }
+      } else {
+        alert.runModal()


This branch is new. We were failing to handle the case where there is no view before.

We could fail like on iOS (see below), but since macOS has a simple way to handle showing an alert without a view I went with that option.

stuartmorgan-g · 2025-06-20T12:23:09Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+      } else {
+        // The Obj-C declaration of evaluatePolicy defines the callback type as NSError*, but the
+        // Swift version is (any Error)?, so provide a fallback in case somehow the type is not
+        // NSError.


This branch is new, for the reason described here.

hellohuanlin · 2025-06-26T19:14:53Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

  var evaluateError: NSError?

  // Overridden as read-write to allow stubbing.
  var biometryType: LABiometryType = .none
  var localizedFallbackTitle: String?

-  func canEvaluatePolicy(_ policy: LAPolicy) throws {
+  func canEvaluatePolicy(_ policy: LAPolicy, error: NSErrorPointer) -> Bool {


curious if this also conforms to the protocol:

func canEvaluatePolicy(_ policy: LAPolicy, error: inout NSError?) -> Bool

The goal is to match LAContext, and what I have here is the signature according to Apple:

https://developer.apple.com/documentation/localauthentication/lacontext/canevaluatepolicy(_:error:)

hellohuanlin · 2025-06-26T19:16:18Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

-      XCTAssertNil(error)
+      switch resultDetails {
+      case .success(let successDetails):
+        XCTAssertEqual(successDetails.result, AuthResult.success)


nit: XCTAssertEqual(successDetails.result, .success)

Done throughout.

hellohuanlin · 2025-06-26T19:21:29Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

-    XCTAssertEqual(result!.count, 1)
-    XCTAssertEqual(result![0].value, FLADAuthBiometric.face)
-    XCTAssertNil(error)
+    do {


here and other tests - we can mark the function signature as throws, and remove this do/catch block

Done throughout.

hellohuanlin · 2025-06-26T19:24:35Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

+    return AuthStrings(
+      reason: "a reason", lockOut: "locked out", goToSettingsButton: "Go To Settings",
+      goToSettingsDescription: "Settings", cancelButton: "Cancel",
+      localizedFallbackTitle: localizedFallbackTitle)


nit: separate lines for each items

(https://google.github.io/swift/ -> Line-Wrapping -> "Comma-delimited lists are only laid out in one direction: horizontally or vertically. ")

Done. I forgot swift-format annoyingly doesn't handle this.

hellohuanlin · 2025-06-26T19:27:02Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+#endif
+
+/// A default context factory that wraps standard LAContext allocation.
+struct DefaultAuthContextFactory: AuthContextFactory {


nit: use class unless we need value semantics of struct (since struct comes with overhead)

What's the overhead? I thought it was the opposite; https://developer.apple.com/documentation/swift/choosing-between-structures-and-classes#Overview says to prefer structs by default.

What's the overhead?

Value types increase both build time and binary size. Though Apple has improved it over the years, so it shouldn't be our key consideration.

The key consideration is whether we want value or reference semantics (which should be the "control identity" in the link you provided)

For example, factories in general should be reference types, because they often share state, so we don't want multiple factories. This particular factory is stateless, so not the end of the world, but still, semantically we don't want multiple factories when passing it around.

The next example is more interesting:

struct DefaultAlertController { var controller: UIAlertController }

If we use value type like here, imagine this code:

let c1 = DefaultAlertController(...) let c2 = c1

Then we have 2 separate values (c1 and c2), but both pointing to the same underlying UIAlertController, which is conceptually misleading (it looks like you have created 2 distinct controllers, but you haven't).

Makes sense! Changed all of them.

hellohuanlin · 2025-06-26T19:55:24Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+  ) {
+    if success {
+      handleResult(succeeded: true, completion: completion)
+    } else {


nit: return in success to reduce indentation?

if success { handle... return } ...

hellohuanlin · 2025-06-26T19:56:24Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+          LAError.biometryLockout,
+          LAError.userFallback,
+          LAError.passcodeNotSet,
+          LAError.authenticationFailed:


nit: can infer these (e.g. case .biometryNotAvailable)

hellohuanlin · 2025-06-26T19:57:24Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+    completion(
+      .success(
+        AuthResultDetails(
+          result: succeeded ? AuthResult.success : AuthResult.failure,


nit: infer type

hellohuanlin · 2025-06-26T20:00:29Z

...th/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/SystemWrappers.swift

+      for sheetWindow: NSWindow,
+      completionHandler handler: ((NSApplication.ModalResponse) -> Void)?
+    )
+    @MainActor


we can mark the whole protocol @MainActor so no need each function. (same below)

This is problematic until we annotate both Pigeon-generated methods and the FlutterPlugin registration methods as @MainActor, because it cascades through other code that ends up in places like the creation of the default implementations in register(with:), which aren't annotated @MainActor even though in practice they are.

It's much easier for now to annotate the specific methods.

hellohuanlin · 2025-06-26T20:01:41Z

...th/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/SystemWrappers.swift

+  /// instances in unit tests.
+  protocol AuthAlertController {
+    @MainActor
+    func addAction(_ action: UIAlertAction)


nit: add a blank line between each members (same below)

stuartmorgan-g

Thanks for the Swift tips!

stuartmorgan-g · 2025-06-27T11:13:32Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

  var evaluateError: NSError?

  // Overridden as read-write to allow stubbing.
  var biometryType: LABiometryType = .none
  var localizedFallbackTitle: String?

-  func canEvaluatePolicy(_ policy: LAPolicy) throws {
+  func canEvaluatePolicy(_ policy: LAPolicy, error: NSErrorPointer) -> Bool {


The goal is to match LAContext, and what I have here is the signature according to Apple:

https://developer.apple.com/documentation/localauthentication/lacontext/canevaluatepolicy(_:error:)

stuartmorgan-g · 2025-06-27T11:20:44Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

-      XCTAssertNil(error)
+      switch resultDetails {
+      case .success(let successDetails):
+        XCTAssertEqual(successDetails.result, AuthResult.success)


Done throughout.

stuartmorgan-g · 2025-06-27T11:22:35Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

-    XCTAssertEqual(result!.count, 1)
-    XCTAssertEqual(result![0].value, FLADAuthBiometric.face)
-    XCTAssertNil(error)
+    do {


Done throughout.

stuartmorgan-g · 2025-06-27T12:04:14Z

packages/local_auth/local_auth_darwin/darwin/Tests/FLALocalAuthPluginTests.swift

+    return AuthStrings(
+      reason: "a reason", lockOut: "locked out", goToSettingsButton: "Go To Settings",
+      goToSettingsDescription: "Settings", cancelButton: "Cancel",
+      localizedFallbackTitle: localizedFallbackTitle)


Done. I forgot swift-format annoyingly doesn't handle this.

stuartmorgan-g · 2025-06-27T12:07:34Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+#endif
+
+/// A default context factory that wraps standard LAContext allocation.
+struct DefaultAuthContextFactory: AuthContextFactory {


Makes sense! Changed all of them.

stuartmorgan-g · 2025-06-27T12:44:20Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+    completion(
+      .success(
+        AuthResultDetails(
+          result: succeeded ? AuthResult.success : AuthResult.failure,


stuartmorgan-g · 2025-06-27T14:03:23Z

...th/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/SystemWrappers.swift

+      for sheetWindow: NSWindow,
+      completionHandler handler: ((NSApplication.ModalResponse) -> Void)?
+    )
+    @MainActor


This is problematic until we annotate both Pigeon-generated methods and the FlutterPlugin registration methods as @MainActor, because it cascades through other code that ends up in places like the creation of the default implementations in register(with:), which aren't annotated @MainActor even though in practice they are.

It's much easier for now to annotate the specific methods.

stuartmorgan-g · 2025-06-27T14:03:28Z

...th/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/SystemWrappers.swift

+  /// instances in unit tests.
+  protocol AuthAlertController {
+    @MainActor
+    func addAction(_ action: UIAlertAction)


stuartmorgan-g · 2025-06-27T14:09:39Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+
+#if os(iOS)
+  /// A default alert controller that wraps UIAlertController.
+  struct DefaultAlertController: AuthAlertController {


stuartmorgan-g · 2025-06-27T14:09:44Z

...h/local_auth_darwin/darwin/local_auth_darwin/Sources/local_auth_darwin/LocalAuthPlugin.swift

+  /// A default alert controller that wraps UIAlertController.
+  struct DefaultAlertController: AuthAlertController {
+    /// The wrapped alert controller.
+    var controller: UIAlertController


stuartmorgan-g added 5 commits June 20, 2025 07:49

First conversion pass

3cd89cd

Idiomatic final block

54f8054

Version bump, podspec

d76aa73

Fix tests and warnings

fbf1103

Undo project changes from building

ece2bf0

stuartmorgan-g requested a review from hellohuanlin June 20, 2025 11:57

stuartmorgan-g requested review from cbracken and vashworth as code owners June 20, 2025 11:57

github-actions bot added p: local_auth platform-ios platform-macos labels Jun 20, 2025

stuartmorgan-g commented Jun 20, 2025

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Replace (any Error) with Error

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stuartmorgan-g added the triage-ios Should be looked at in iOS triage label Jun 23, 2025

hellohuanlin reviewed Jun 26, 2025

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stuartmorgan-g commented Jun 27, 2025

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[local_auth] Convert iOS/macOS to Swift #9459

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stuartmorgan-g commented Jun 20, 2025

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hellohuanlin Jun 26, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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hellohuanlin Jun 26, 2025 •

edited

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