[docs] Add possible remedy for Hermes debugger problems when the project is not served on LAN connection

[Nantris]

To clarify: the remedy works, just can't guarantee it works for everyone.

Why

Hermes troubleshooting steps helped to uncover the problem, but not solve it.

Checklist

• Documentation is up to date to reflect these changes (eg: https://docs.expo.dev and README.md).
• Conforms with the Documentation Writing Style Guide
• This diff will work correctly for expo prebuild & EAS Build (eg: updated a module plugin). (N/A)

[amandeepmittal]

Thanks for adding the remedy. Left a small suggestion to have consistent verbiage.

[Nantris]

@amandeepmittal thanks for the edit. I've found it may also be necessary to --clear-cache once the issue has occurred on a non-working method.

ie --lan doesn't work, so you try tunnel - but --tunnel will only work if you use --tunnel --clear-cache (but --clear-cache alone seems to have no effect.) I'm not sure how to update the wording to reflect that new finding. Any suggestion?

[amandeepmittal]

@slapbox, I don't think --clear-cache is a valid flag for npx expo start. Are you using the local versioned CLI that comes with Expo package in your project?

[Nantris]

Are you using the local versioned CLI that comes with Expo package in your project?

Yes, via yarn expo start

[amandeepmittal]

The flag is --clear. You can also check that by running yarn expo start --help inside the Expo project.

Here is an output of that command:

I'm not sure why you are running --clear-cache and why is it working in your case but you did mention it has no effect. I also don't think -c or --clear is necessary with --tunnel. The purpose of the flag is when there are changes in babel.config.js file or when some things are done with symlinks, in those cases, the flag is required.

[Nantris]

Not sure what to say. I can only report what has worked here. Perhaps passing an invalid flag somehow influences whether the debugger can connect or not. Or maybe I was using --clear and I'm conflating it with --clear-cache in EAS.

I'll loop back next time I run into this issue and report what worked.

[amandeepmittal]

No worries at all! Feel free to open an issue if you find anything weird 😄

I'm going to merge this with the current changes. Thanks for your contribution!!!

[Nantris]

@amandeepmittal, just an update: these days (with SDK 48) I'm noticing yarn expo start --lan almost always works without any other flags needed. I never need to clear the cache anymore for it to work but I always need --lan or I get the message about the debugger only working with Hermes apps.