Warn when browser or dev are used

[benmccann]

Describe the problem

People use import { browser, dev } from '$app/environment' and then their packages end up being tied to SvelteKit and Vite when they should work with any Svelte project

Describe the proposed solution

Print a big loud warning when running svelte-package if anyone tries to use import.meta.env.SSR, import { browser, dev } from '$app/environment', etc. and tell them to use import { BROWSER, DEV } from 'esm-env' unless they intend for their package to only be used in SvelteKit

Put a warning in the docs not to use these for libraries

Alternatives considered

Get rid of import { browser, dev } from '$app/environment' and just tell people to use esm-env in the docs. I think I'd prefer that honestly, but it couldn't be done until SvelteKit 2 as it's a breaking change

Importance

nice to have

Additional Information

No response

[Tal500]

Please notice @benmccann that there is a problem with the REPL, I filled up an issue: benmccann/esm-env#1

[Conduitry]

We should move forward with this change regardless. Using $app/environment in components already doesn't work in the REPL, and so pushing people towards esm-env won't make them worse off. The REPL is a lot more likely to support exports maps in the future than it is to ever support a hacky workaround specifically for $app/environment when that's syntac we discourage people from using anywhere else.

[orefalo]

Hi, can you have a look at https://github.com/Tal500/esm-env-robust and confirm it's a valid workaround for the expected behavior?
If it is, can we push the code upstream to the svelte kit implementation, so that the environment api behaves as expected?

[Glench]

Would really love to use the alternative — use esm-env directly. I'm running into issues trying to use stuff in my SvelteKit app in utility scripts and in the node REPL.

[ghostdevv]

Should be able to close this now

kit/packages/package/src/validate.js

Line 46 in 7243694

'Avoid usage of `$app/environment` in your code, if you want to library to work for people not using SvelteKit (only regular Svelte, for example). ' +