Add 'VITE_' prefix to SvelteKit framework

[domeccleston]

📋 Checklist

Since SvelteKit uses Vite under the hood, it needs the _VITE environment variable prefix. This adds it.

Example which reproduces the Svelte Kit example with undefined environment variables:

• Repo
• Preview

Tests

Currently I get an error when trying to run the tests: Module ts-jest in the transform option was not found.

• The code changed/added as part of this PR has been covered with tests
• All tests pass locally with yarn test-unit

Code Review

• This PR has a concise title and thorough description useful to a reviewer
• Issue from task tracker has a link to this PR

[codecov]

Codecov Report

Merging #6821 (23766ec) into main (0505f4e) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #6821   +/-   ##
=======================================
  Coverage   49.17%   49.17%           
=======================================
  Files         135      135           
  Lines        5426     5426           
  Branches     1358     1358           
=======================================
  Hits         2668     2668           
  Misses       2745     2745           
  Partials       13       13           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0505f4e...23766ec. Read the comment docs.

[leerob]

You might want to check with @styfle, I believe changing the env var preset is considered a breaking change here. Did SvelteKit change this under the hood?

[raymclee]

Is it the reason I cannot get SVELTEKIT_VERCEL_URL on vercel?

[styfle]

Thanks!

[TooTallNate]

Thanks @domeccleston!

[devunt]

This should be updated to PUBLIC_ prefix, according to the newly released SvelteKit v1.0 docs [1]

[1] https://kit.svelte.dev/docs/configuration#env

[Rich-Harris]

We actually don't want a prefix here, because it would cause the values to be available via $env/static/public and $env/dynamic/public, when they only need to be available on the server (via $env/static/private and $env/dynamic/private).

In particular, adding them to public env will mean they're included in every rendered HTML page (because that's how $env/dynamic/public is populated), which is undesirable.