Is running packager by calling react-native internal script still necessary for run-android?

[MateWW]

Background

I'm actively working on preparing a react-native monorepo template with enabled hoisting.
I've everything working besides one thing.
When I'm running react-native run-android packager is starting from monorepo root(./) instead of app package ./apps/app
I can workaround it by running packager upfront but I would love to have that template working without such workarounds.

Findings

I've dived deeply into how I can work around it and figured out that there is no option to solve that without patching react-native.

Why is that?

Current flow

Currently running packager for run-android is working the following way:

• CLI is calling startServerInNewWindow
• startServerInNewWindow
  • is overriding .packager.env
  • and is calling lauchPackager.sh
• lauchPackager.sh is calling packager.sh
• packager.sh is calling react-native start from PROJECT_ROOT which is statically set to the path relative to node_modules/react-native

Why is that a problem?

1. Currently the simplest option to change PROJECT_ROOT from CLI perspective is to overwrite PROJECT_ROOT environment variable inside .packager.env

   • In the currently released react-native 0.71 packager.sh is always overwriting PROJECT_ROOT path with a path relative to the script location.
   • In future version(react-native master) there it accepts PROJECT_ROOT from outside.
   • Sadly there is still this condition that will overwrite this path because in monorepo we have hoisting so the react-native package is located in monorepo root instead PROJECT_ROOT

2. Generally configuration of react-native start from CLI perspective is limited.
   It seems that packager.sh accepts additional arguments (with "$@" at the end) that will be forwarded to react-native start.
   However launchPackager.command is not forwarding it from CLI

Question

1. I'm curious what is the story behind this solution where CLI have to call react-native internal script that will call CLI.
   Maybe there is someone who has some background on this one?

2. Is this script treated internally in react-native as something that should be used by the community?
   This question is based on this comment inside packager.sh that sounds like it is something for internal react-native testing.

3. If this is something that should be used by the community then I'm wondering if there is a way to make it more configurable from a CLI perspective.

Reproducible demo:

• clone repo https://github.com/MateWW/react-native-new-arch-monorepo
• install dependencies
• make sure you have packager running
• trigger yarn android(doesn't matter if you will do that from app directory or root)

[cortinico]

Is this script treated internally in react-native as something that should be used by the community?
This question is based on this comment inside packager.sh that sounds like it is something for internal react-native testing.

Yup so packager.sh should not be used externally. That's a script we use to invoke Metro for RN Tester. The CLI should not invoke it

[thymikee]

@szymonrybczak is on it

[cortinico]

Yup so packager.sh should not be used externally. That's a script we use to invoke Metro for RN Tester. The CLI should not invoke it

Also this explains why we had user reports of issues like:

• MacOS: realpath not found react/react-native#34146

[MateWW]

@cortinico
I'm reviewing IOS because it also has a problem with launching packager in my monorepo.
I found that inside react-native you are also using this lauchPackager.command for IOS.
This time it's internally inside react-native during Start Packager build phase.
Do you think this should be unified somehow across both platforms?