Support configuring WP_HOME with alternate port

[joemcgill]

Is your feature request related to a problem? Please describe.
I want to use @wordpress/env to create an environment to test a headless WordPress application where the front end will be run from a node application running outside of the Env's docker setup. To do this, I want to be able to specify a WP_HOME like http://localhost:3001 in my .wp-env.json file and have the port specified be respected.

However, right now the withOverrides() function in config/config.js overrides the port with the port of the environment specified.

Describe the solution you'd like
I'd like to see withOverrides() check to see if a port value is set for WP_HOME before overriding it here: https://github.com/WordPress/gutenberg/blob/master/packages/env/lib/config/config.js#L262 I think overriding the WP_TESTS_DOMAIN and WP_SITEURL probably makes sense to leave as is.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

[noahtallen]

@joemcgill I'm not super familiar with how these settings are often used. I coded them to be the same because I had some trouble when they were different :) Is there a reason why using the same port for each of these URLs won't work?

What kind of use case would this enable, out of curiosity?

[joemcgill]

Hi @noahtallen, like I described in the issue description, I'm wanting to use wp-env run the backend for a headless site where WP_HOME points to a separate node application. Right now, if I have a headless front end running on a different port than the WP container and attempt to set WP_HOME to that application (i.e., the front end should be localhost:3030 and wp-env is on localhost:8888) then this function strips off the port that I supplied in my .wp-env.json file and replaces it with the port for the WP container (i.e. 8888).

[joemcgill]

I put together a PR that I think takes care of this, but I may be missing something so would appreciate feedback!

[noahtallen]

Interesting use case! Thanks for clarifying, I appreciate understanding that better. I'll take a look at your PR now :)