[google_maps_flutter] Convert plugin class to Swift

[stuartmorgan-g]

Converts the top-level plugin class and its supporting platform view factory from Objective-C to Swift. This changes very little implementation, but lays the groundwork for future incremental conversions.

Part of flutter/flutter#119108

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I linked to at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or I have commented below to indicate which version change exemption this PR falls under¹.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style, or I have commented below to indicate which CHANGELOG exemption this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩² ↩³

[gemini-code-assist]

Code Review

This pull request successfully converts the top-level plugin class and its associated platform view factory from Objective-C to Swift. The changes are well-contained and include necessary updates to the podspec, module definitions, and test files to support the new Swift implementation. The core logic, including the handling of shared GMSServices, is correctly preserved.

My review includes one suggestion to improve the robustness of the new Swift code by replacing force-unwrapping and force-casting with guard statements. This will make the plugin more resilient to unexpected inputs and prevent potential crashes.

[gemini-code-assist]

The use of force casting (as!) and force unwrapping (!) can make the app crash if the assumptions about args type or registrar being non-nil are violated. It's safer to use guard let with conditional casting (as?) and optional binding to validate these before use. This provides more robust error handling and clearer failure messages if something goes wrong, which is especially useful for plugin consumers.

Also, using _ = ... is more idiomatic for calling something for its side effects while ignoring the result, which avoids an 'unused variable' warning.

    // Precache shared map services, if needed. Initializing this prepares GMSServices
    // on a background thread controlled by the GoogleMaps framework.
    _ = GoogleMapFactory.sharedMapServices

    guard let creationParams = args as? FGMPlatformMapViewCreationParams else {
      // This is a programmer error on the Dart side, so crashing is reasonable.
      fatalError("Invalid creation parameters for Google Map: \(String(describing: args))")
    }
    guard let registrar = self.registrar else {
      // This should not happen in a normal lifecycle.
      fatalError("Registrar is nil when creating Google Map.")
    }

    return FLTGoogleMapController(
      frame: frame, viewIdentifier: viewId,
      creationParameters: creationParams, registrar: registrar)

[stuartmorgan-g]

This test is removed because it was testing that this code and its supported declarations were all wired up correctly, and in Swift having a lazy type (class-level) variable is a built-in language feature and all of that code is just this line now, so there's nothing meaningful to test now.

[stuartmorgan-g]

Well, this is fun. We appear to have a SwiftPM-style problem with CocoaPods as well if we adopt any Swift in the target:

Swift Compiler Error (Xcode): Compiling for iOS 14.0, but module 'GoogleMapsUtils' has a minimum deployment target of iOS 15.0:

It goes away if I change the podspec's s.platform = :ios, '14.0' to s.platform = :ios, '15.0', even though this is compiling the iOS 15 example app and thus shouldn't actually be compiling anything for iOS 14 regardless.

[stuartmorgan-g]

I'll revisit this once we restructure the plugin to handle SwiftPM, since that should resolve this as well.

[stuartmorgan-g]

Closing since I'll need to revisit this for the multi-implementation world.