update snowpack to v3.0

[FredKSchott]

Before submitting the PR, please make sure you do the following

• Updated Snowpack & Snowpack Svelte plugin to latest v3.0 (published today, announcement coming tomorrow).
• Updated code to final v3 interface changes.
• Lots of bug fixes and improvements, but overall no huge changes to how Snowpack works in this setup. I know @samccone had mentioned our new streaming imports feature, but that is not enabled in Snowpack by default.
• Question: We've merged in support for your loader as snowpack.getESMRuntime(). LMK if you'd like me to update SvelteKit to use that implementation and get rid of the custom loader.js that you all have here.

Tests

• Question: Examples are currently failing with a NOT_FOUND error that I can't track down. From the logs, it looks like something server-side is requesting foo.js instead of the new v3.0 foo.svelte.js. I looked around for where that was happening, but couldn't find it. @Rich-Harris And ideas?

[Rich-Harris]

thank you @FredKSchott! and congrats on 3.0 🎉

as mentioned in FredKSchott/snowpack#2260, I'm slightly unclear on the file renaming rules — another thing that I've noticed is that sometimes component imports become foo.svelte.proxy.js, but that URL doesn't work (it needs to be foo.svelte.js). Currently working around it in the hackiest way possible, but perhaps you have some insight into what's happening there?

[FredKSchott]

Hmm, foo.svelte.proxy.js is definitely unexpected. If you can point me to a branch where this is happening (or just what lines to remove on master to fix) then I'm happy to take a look

[Rich-Harris]

@FredKSchott if you just comment out these lines...

kit/packages/kit/src/api/dev/loader.js

Line 48 in eac3225

url = url.replace('.svelte.proxy', '.svelte');

kit/packages/kit/src/api/dev/index.js

Line 133 in eac3225

req.url = req.url.replace('.svelte.proxy', '.svelte');

...then try to pnpm dev any of the projects in examples, or try pnpm test inside test/apps/basic, you'll see it fail

[FredKSchott]

Found the issue: #323