Add-to-add host app won't build when flutter app has plugins - linker error Library not found #35901
Description
Add a flutter sub-app with plugins to an existing app messes up the host app's Xcode build settings, which causes various build issue. In a new add-to-app I tried to make, it manifested as linker errors because the framework search paths were incorrect.
Steps to Reproduce
The wonky build settings can be seen with the ios_add2app integration test, though it somehow is able to build successfully
$ cd dev/integration_tests/ios_add2app/flutterapp
$ flutter build ios
$ cd ..
$ xcodebuild -showBuildSettings -configuration Debug | grep -E "LIBRARY_SEARCH_PATHS|SYMROOT"
LIBRARY_SEARCH_PATHS = "/Projects/flutter/dev/integration_tests/build/ios/Debug-iphoneos/FlutterPluginRegistrant"
LOCSYMROOT =
SYMROOT = /Projects/flutter/dev/integration_tests/build/ios
"flutter/dev/integration_tests/build/ios" doesn't exist.
SYMROOT should be /Projects/flutter/dev/integration_tests/ios_add2app/ and LIBRARY_SEARCH_PATHS should be /Projects/flutter/dev/integration_tests/ios_add2app/flutterapp/build/ios/Debug-iphoneos/FlutterPluginRegistrant