Unknown type name 'import'

AwesomeProject.zip

Description

After switching to AppDelegate.swift xcode started giving this error

Steps to reproduce

1. Update rn version from 0.76 to 0.77/0.78
2. Update AppDelegate.mm file to AppDelegate.swift
3. Delete main.m and AppDelegate.h
4. build via xcode

React Native Version

0.78.0

Affected Platforms

Build - MacOS

Output of npx @react-native-community/cli info

System:
  OS: macOS 15.2
  CPU: (8) arm64 Apple M1
  Memory: 89.20 MB / 8.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 18.18.0
    path: ~/.nvm/versions/node/v18.18.0/bin/node
  Yarn:
    version: 1.22.22
    path: /usr/local/bin/yarn
  npm:
    version: 9.8.1
    path: ~/.nvm/versions/node/v18.18.0/bin/npm
  Watchman:
    version: 4.7.0
    path: /usr/local/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /usr/local/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 24.2
      - iOS 18.2
      - macOS 15.2
      - tvOS 18.2
      - visionOS 2.2
      - watchOS 11.2
  Android SDK: Not Found
IDEs:
  Android Studio: 2020.3 AI-203.7717.56.2031.7583922
  Xcode:
    version: 16.2/16C5032a
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 11.0.1
    path: /usr/bin/javac
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 15.0.1
    wanted: 15.0.1
  react:
    installed: 19.0.0
    wanted: 19.0.0
  react-native:
    installed: 0.78.0
    wanted: 0.78.0
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: false
iOS:
  hermesEnabled: true
  newArchEnabled: false

Stacktrace or Logs

AppDelegate.swift:1:1: error: unknown type name 'import'
    1 | import UIKit
AppDelegate.swift:1:13: error: expected ';' after top level declarator
    1 | import UIKit

Reproducer

git repo

Screenshots and Videos

Start with the linked reproducer and the AppDelegate.swift migration, then compare it with the removed AppDelegate.mm, main.m, and AppDelegate.h files. Build the project through Xcode and trace why the Swift file is being parsed as another source type; done means the React Native 0.78 project builds without the reported errors.