Problem

When using SwiftPM, the Flutter tool generates a Package.swift file that adds plugins to the app's builds. This Package.swift's supported platforms should match the Xcode project's Minimum Deployments.

However, if in Xcode I update my Minimum Deployments and then do a build, the Package.swift file isn't updated to the latest supported platforms. See: #162072

Repro

1. Create an app with a plugin:

   flutter create my_app
   cd my_app
   flutter pub add url_launcher
   

2. Generate the project configuration with SwiftPM on:

   flutter config --enable-swift-package-manager
   flutter build ios --config-only
   

3. Open the project in Xcode:

   open ios/Runner.xcworkspace
   

4. In Xcode, open Project Navigator > Package Dependencies > FlutterGeneratedPluginSwiftPackage.

   Check the generated package's supported platforms:

   let package = Package(
       name: "FlutterGeneratedPluginSwiftPackage",
       platforms: [
           .iOS("12.0")
       ],
       ...
   )

5. In Xcode, open Runner target > General > Minimum Deployments and set iOS to 15.0

6. In Xcode, build the app

7. Check the generated package's supported platforms. It will still be .iOS("12.0") ❌

Workaround

To fix this, build the app using the Flutter tool:

flutter build ios --config-only

This regenerates the Package.swift file and updates its supported platforms.