Hermes: Use published hermes-engine for tagged RN releases

Differential Revision: D36533683

fbshipit-source-id: 6bdac8057f091815ff4338ae36669137439f4903

scripts/react_native_pods.rb

@@ -3,6 +3,7 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 
+require 'json'
 require 'pathname'
 require_relative './react_native_pods_utils/script_phases.rb'
 require_relative './cocoapods/flipper.rb'
@@ -102,10 +103,23 @@ def use_react_native! (options={})
  end
 
  if hermes_enabled
- system("(cd #{prefix} && node scripts/hermes/prepare-hermes-for-build)")
  pod 'React-hermes', :path => "#{prefix}/ReactCommon/hermes"
- pod 'hermes-engine', :path => "#{prefix}/sdks/hermes/hermes-engine.podspec"
  pod 'libevent', '~> 2.1.12'
+
+ sdks_dir = Pod::Config.instance.installation_root.join(prefix, "sdks")
+ hermes_tag_file = sdks_dir.join(".hermesversion")
+
+ if (File.exist?(hermes_tag_file))
+ # Use published pod with pre-builts.
+ package = JSON.parse(File.read(File.join(__dir__, "..", "package.json")))
+ hermes_version = package['version']
+ pod 'hermes-engine', hermes_version
+ else
+ # Use local podspec and build from source.
+ system("(cd #{relative_path_from(Pod::Config.instance.installation_root).to_s} && node scripts/hermes/prepare-hermes-for-build)")
+ pod 'hermes-engine', :path => "#{prefix}/sdks/hermes/hermes-engine.podspec"
+ end
+
  end
 
  pods_to_update = LocalPodspecPatch.pods_to_update(options)