This old-style function definition is not preceded by a prototype

I had the same problem and it was fixed

• rm Pods, Podfile

• Pod init

In Podfile delete all and add:

Uncomment this line to define a global platform for your project

platform :ios, '9.0'

CocoaPods analytics sends network stats synchronously affecting flutter build latency.

ENV['COCOAPODS_DISABLE_STATS'] = 'true'

project 'Runner', {
 'Debug' => :debug,
 'Profile' => :release,
 'Release' => :release,
}

def flutter_root
 generated_xcode_build_settings_path = File.expand_path(File.join('..', 'Flutter', 'Generated.xcconfig'), __FILE__)
 unless File.exist?(generated_xcode_build_settings_path)
  raise "#{generated_xcode_build_settings_path} must exist. If you're running pod install manually, make sure flutter pub get is executed first"
 end

 File.foreach(generated_xcode_build_settings_path) do |line|
  matches = line.match(/FLUTTER_ROOT\=(.*)/)
  return matches[1].strip if matches
 end
 raise "FLUTTER_ROOT not found in #{generated_xcode_build_settings_path}. Try deleting Generated.xcconfig, then run flutter pub get"
end

require File.expand_path(File.join('packages', 'flutter_tools', 'bin', 'podhelper'), flutter_root)

flutter_ios_podfile_setup

target 'Runner' do
 use_frameworks!
 use_modular_headers!

 flutter_install_all_ios_pods File.dirname(File.realpath(__FILE__))
  pod 'Firebase/Analytics'
  pod 'Firebase/Auth'
  pod 'Firebase/Firestore'
  pod 'Firebase/Crashlytics'
  pod 'Firebase/Messaging'
end

post_install do |installer|
 installer.pods_project.targets.each do |target|
  flutter_additional_ios_build_settings(target)
 end
end

• Pod install

Good luck