Create Helper to read the package.json from Cocoapods

Summary:
This diff introduce an helper to read the content of the React Native package of json from ruby.

## Changelog:
[iOS][Added] - Add helper to read the package.json from the cocoapods script.

Differential Revision: D49146946

fbshipit-source-id: 842c0d1300399d80b9de64cb6ec633c2ba987c35

packages/react-native/scripts/cocoapods/__tests__/new_architecture-test.rb

@@ -8,10 +8,12 @@
 require_relative "./test_utils/InstallerMock.rb"
 require_relative "./test_utils/PodMock.rb"
 require_relative "./test_utils/SpecMock.rb"
+require_relative "./test_utils/FileMock.rb"
 
 class NewArchitectureTests < Test::Unit::TestCase
     def teardown
         Pod::UI.reset()
+        FileMock.reset()
     end
 
     # ============================= #
@@ -266,6 +268,34 @@ def test_isNewArchEnabled_whenOnGreaterThan100AndFlagFalse_returnTrue
 
         assert_equal("1", isEnabled)
     end
+
+    # =================================== #
+    # Test - Extract React Native Version #
+    # =================================== #
+    def test_extractReactNativeVersion_whenFileDoesNotExists_raiseError()
+        react_native_path = './node_modules/react-native/'
+
+        exception = assert_raise(RuntimeError) do
+            NewArchitectureHelper.extract_react_native_version(react_native_path, :file_manager => FileMock)
+        end
+
+        assert_equal("Couldn't find the React Native package.json file at ./node_modules/react-native/package.json", exception.message)
+    end
+
+    def test_extractReactNativeVersion_whenFileExists_returnTheRightVersion()
+        react_native_path = "./node_modules/react-native/"
+        full_path = File.join(react_native_path, "package.json")
+        json = "{\"version\": \"1.0.0-prealpha.0\"}"
+        FileMock.mocked_existing_files([full_path])
+        FileMock.files_to_read({
+            full_path => json
+        })
+
+        version = NewArchitectureHelper.extract_react_native_version(react_native_path, :file_manager => FileMock)
+
+        assert_equal("1.0.0-prealpha.0", version)
+    end
+
 end
 
 # ================ #

packages/react-native/scripts/cocoapods/new_architecture.rb

@@ -3,6 +3,8 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 
+require 'json'
+
 class NewArchitectureHelper
     @@shared_flags = "-DFOLLY_NO_CONFIG -DFOLLY_MOBILE=1 -DFOLLY_USE_LIBCPP=1"
 
@@ -159,6 +161,15 @@ def self.folly_compiler_flags
         return @@folly_compiler_flags
     end
 
+    def self.extract_react_native_version(react_native_path, file_manager: File, json_parser: JSON)
+        package_json_file = File.join(react_native_path, "package.json")
+        if !file_manager.exist?(package_json_file)
+            raise "Couldn't find the React Native package.json file at #{package_json_file}"
+        end
+        package = json_parser.parse(file_manager.read(package_json_file))
+        return package["version"]
+    end
+
     def self.is_new_arch_enabled(new_arch_enabled, react_native_version)
         regex = /^(\d+)\.(\d+)\.(\d+)(?:-(\w+(?:[-.]\d+)?))?$/