Simplify furthermore App migration

Summary:
This Diff adds a couple of APIs to the `react_native_pods.rb` file to simplify further the migration to the New Architecture for the iOS app.
Specifically, it aims to simplify [this](https://reactnative.dev/docs/next/new-architecture-app-intro#ios---build-the-project) steps by offering a RN-managed min version and creating the .xcode.env file for the user if it is missing.

## Changelog

[iOS][Added] - Add new API to simplify app migration

Reviewed By: cortinico

Differential Revision: D39469599

fbshipit-source-id: f0323e86c83c2731671fcd5bb4288071304bb43b

packages/rn-tester/Podfile

@@ -1,11 +1,9 @@
 require_relative '../../scripts/react_native_pods'
 
 source 'https://cdn.cocoapods.org/'
-platform :ios, '12.4'
+platform :ios, min_ios_version_supported
 
-# Temporary solution to suppress duplicated GUID error.
-# Can be removed once we move to generate files outside pod install.
-install! 'cocoapods', :deterministic_uuids => false
+prepare_react_native_project!
 
 USE_FRAMEWORKS = ENV['USE_FRAMEWORKS'] == '1'
 IN_CI = ENV['CI'] == 'true'

scripts/cocoapods/__tests__/utils-test.rb

@@ -10,14 +10,27 @@
 require_relative "./test_utils/InstallerMock.rb"
 require_relative "./test_utils/EnvironmentMock.rb"
 require_relative "./test_utils/SysctlCheckerMock.rb"
+require_relative "./test_utils/FileMock.rb"
+require_relative "./test_utils/systemUtils.rb"
+require_relative "./test_utils/PathnameMock.rb"
 
 class UtilsTests < Test::Unit::TestCase
+    def setup
+        @base_path = "~/app/ios"
+        Pathname.pwd!(@base_path)
+        File.enable_testing_mode!
+    end
+
     def teardown
+        File.reset()
         Pod::UI.reset()
+        Pathname.reset()
+        Pod::Config.reset()
         SysctlChecker.reset()
         Environment.reset()
         ENV['RCT_NEW_ARCH_ENABLED'] = '0'
         ENV['USE_HERMES'] = '1'
+        system_reset_commands
     end
 
     # ======================= #
@@ -443,6 +456,29 @@ def test_setNodeModulesUserSettings_addTheUserSetting
         assert_equal(pods_projects_mock.save_invocation_count, 1)
         assert_equal(Pod::UI.collected_messages, ["Setting REACT_NATIVE build settings"])
     end
+
+    # =================================== #
+    # Test - Prepare React Native Project #
+    # =================================== #
+    def test_createXcodeEnvIfMissing_whenItIsPresent_doNothing
+        # Arrange
+        File.mocked_existing_files("/.xcode.env")
+        # Act
+        ReactNativePodsUtils.create_xcode_env_if_missing
+        # Assert
+        assert_equal(File.exist_invocation_params, ["/.xcode.env"])
+        assert_equal($collected_commands, [])
+    end
+
+    def test_createXcodeEnvIfMissing_whenItIsNotPresent_createsIt
+        # Arrange
+
+        # Act
+        ReactNativePodsUtils.create_xcode_env_if_missing
+        # Assert
+        assert_equal(File.exist_invocation_params, ["/.xcode.env"])
+        assert_equal($collected_commands, ["echo 'export NODE_BINARY=$(command -v node)' > /.xcode.env"])
+    end
 end
 
 def prepare_empty_user_project_mock

scripts/cocoapods/utils.rb

@@ -152,5 +152,13 @@ def self.fix_library_search_path(config)
         end
     end
 
+    def self.create_xcode_env_if_missing
+        relative_path = Pod::Config.instance.installation_root.relative_path_from(Pathname.pwd)
+        file_path = File.join(relative_path, '.xcode.env')
+        if File.exist?(file_path)
+            return
+        end
 
+        system("echo 'export NODE_BINARY=$(command -v node)' > #{file_path}")
+    end
 end

scripts/react_native_pods.rb

@@ -23,6 +23,23 @@
 
 $START_TIME = Time.now.to_i
 
+# This function returns the min iOS version supported by React Native
+# By using this function, you won't have to manualy change your Podfile
+# when we change the minimum version supported by the framework.
+def min_ios_version_supported
+  return '12.4'
+end
+
+# This function prepares the project for React Native, before processing
+# all the target exposed by the framework.
+def prepare_react_native_project!
+  # Temporary solution to suppress duplicated GUID error.
+  # Can be removed once we move to generate files outside pod install.
+  install! 'cocoapods', :deterministic_uuids => false
+
+  ReactNativePodsUtils.create_xcode_env_if_missing
+end
+
 # Function that setup all the react native dependencies
 # 
 # Parameters

template/ios/Podfile

@@ -1,8 +1,8 @@
 require_relative '../node_modules/react-native/scripts/react_native_pods'
 require_relative '../node_modules/react-native/scripts/native_modules'
 
-platform :ios, '12.4'
-install! 'cocoapods', :deterministic_uuids => false
+platform :ios, min_ios_version_supported
+prepare_react_native_project!
 
 flipper_config = ENV['NO_FLIPPER'] == "1" ? FlipperConfiguration.disabled : FlipperConfiguration.enabled