[jessieAnhNguyen]

Summary:

---

This PR implements a new command to download the Hermes Sampling Profiler to a local machine.

This command is built as part of the goal to visualize the performance of JavaScript running on Hermes in a React Native app.
@saphal1998 and I worked on this under @axemclion and @jevakallio guidance.

1. Purpose:

• This new command helps users convert a Hermes tracing profile to Chrome tracing profile and pull it to the local machine
• Instructions on how to use Hermes: Using Hermes
• The hermes-profile-transformer tool that converts Hermes tracing profile to Chrome tracing profile Hermes-profile-transformer package

2. Usage:

react-native profile-hermes [destinationDir] <flag>

• destinationDir is optional; if provided, pull the file to that directory

  default: pull to the current React Native app root directory

Options

• --filename [string]

File name of the profile to be downloaded, ex. sampling-profiler-trace8593107139682635366.cpuprofile

default: pull the latest file

• --verbose

Lists commands and steps that are run internally to pull the file from Android device

• --raw

Pulls the original Hermes tracing profile without any transformation

• --sourcemap-path [string]

The local path to your source map file if you generated it manually, ex. /tmp/sourcemap.json

• --generate-sourcemap

Generate the JS bundle and source map in os.tmpdir()

Notes on source map

• Source map is used to enhance the profile and associate trace events with the application code
• This step is recommended in order for the source map to be generated:

If you are planning on building a debug APK, that will run without the packager, by invoking ./gradlew assembleDebug you can simply set bundleInDebug: true in your app/build.gradle file, inside the project.ext.react map.

Test Plan:

---

• yarn
• yarn lint
• Test on a React Native app: follow the instructions on the CLI's Testing Plan
• Command react-native profile-hermes as per instruction above

Example output of running the command

[BrendonSled]

is there no appId flag?

Would really be nice to have this included:

cli/packages/platform-android/src/commands/runAndroid/tryLaunchAppOnDevice.ts

Line 19 in 5ec3fcf

const {appId, appIdSuffix} = args;