Add use_react_native_codegen!

Summary:
Consolidate CocoaPods codegen scripts under a single `use_react_native_codegen!` method in `react_native_pods.rb`.

This is the first step towards making the codegen scripts library-agnostic. There are still a handful of hardcoded assumptions in place (e.g. the output directory structure, the use of a separate directory for components), but with some work one would be able to add codegen support to arbitrary CocoaPods podspecs.

The codegen script no longer takes a CODEGEN_PATH argument, and will instead attempt to use the local react-native-codegen package if available, and fallback to using the node_modules/react-native-codegen package if not.

## Usage

The `use_react_native_codegen!` method has two arguments:

- `spec`, a pod [Specification](https://www.rubydoc.info/github/CocoaPods/Core/Pod/Specification) object.
- `options`, an optional object. Supported keys:
  - `:srcs_dir`, the path to your JavaScript sources. Your native module or component specs should be located somewhere in this directory.

Changelog: [Internal]

Reviewed By: mdvacca

Differential Revision: D25728053

fbshipit-source-id: feec587b656d5b220598ce6196ea6bb34a9580a9

Libraries/FBReactNativeSpec/FBReactNativeSpec.podspec

@@ -4,44 +4,19 @@
 # LICENSE file in the root directory of this source tree.
 
 require "json"
+require_relative "../../scripts/react_native_pods.rb"
 
 package = JSON.parse(File.read(File.join(__dir__, "..", "..", "package.json")))
 version = package['version']
 
 source = { :git => 'https://github.com/facebook/react-native.git' }
-codegen_path_prefix = ".."
 if version == '1000.0.0'
   # This is an unpublished version, use the latest commit hash of the react-native repo, which we’re presumably in.
   source[:commit] = `git rev-parse HEAD`.strip
-  codegen_path_prefix = "packages"
 else
   source[:tag] = "v#{version}"
 end
 
-react_native_path = File.join(__dir__, "..", "..")
-srcs_dir = File.join(__dir__, "..")
-codegen_script_path = File.join(react_native_path, "scripts", "generate-specs.sh")
-codegen_path = File.join(react_native_path, codegen_path_prefix, "react-native-codegen")
-codegen_command = "CODEGEN_PATH=#{codegen_path} sh '#{codegen_script_path}' | tee \"${SCRIPT_OUTPUT_FILE_0}\""
-modules_output_dir = File.join(__dir__, "FBReactNativeSpec")
-components_output_dir = File.join(react_native_path, "ReactCommon", "react", "renderer", "components", "rncore")
-generated_filenames = [ "FBReactNativeSpec.h", "FBReactNativeSpec-generated.mm" ]
-generated_files = generated_filenames.map { |filename| File.join(modules_output_dir, filename) }
-
-if ENV['USE_FABRIC'] == '1'
-  components_generated_filenames = [
-    "ComponentDescriptors.h",
-    "EventEmitters.cpp",
-    "EventEmitters.h",
-    "Props.cpp",
-    "Props.h",
-    "RCTComponentViewHelpers.h",
-    "ShadowNodes.cpp",
-    "ShadowNodes.h"
-  ]
-  generated_files = generated_files.concat(components_generated_filenames.map { |filename| File.join(components_output_dir, filename) })
-end
-
 folly_compiler_flags = '-DFOLLY_NO_CONFIG -DFOLLY_MOBILE=1 -DFOLLY_USE_LIBCPP=1 -Wno-comma -Wno-shorten-64-to-32'
 folly_version = '2020.01.13.00'
 
@@ -72,12 +47,5 @@ Pod::Spec.new do |s|
   s.dependency "React-jsi", version
   s.dependency "ReactCommon/turbomodule/core", version
 
-  s.prepare_command = "mkdir -p #{modules_output_dir} #{components_output_dir} && touch #{generated_files.reduce() { |str, file| str + " " + file }}"
-  s.script_phase = {
-    :name => 'Generate Specs',
-    :input_files => [srcs_dir],
-    :output_files => ["$(DERIVED_FILE_DIR)/codegen.log"],
-    :script => codegen_command,
-    :execution_position => :before_compile
-  }
+  use_react_native_codegen! (s)
 end