Bundle CSS file if CSS is not injected to DOM

[akihikodaki]

VueAsset does this, so why doesn't SvelteAsset?

Some design questions:

• Shouldn't compilerOptions.css be false by default? This would be a breaking change, of course. However, it would bring consistency with CSSAsset and VueAsset.
• It uses CSSAsset to post-transform CSS, but is it really fine? It already has preprocess to transform CSS, and this feature is kind of redundant. I decided to use the class, however, because it already employs JSAsset to transform JavaScript output, and the CSSAsset brings an important feature: to resolve url(./foo.png).

[DeMoorJasper]

Thank you so much for the PR!

I think it should be fine to just do it the same as vue without having the internal css parsing? What do you think? (removing CSSAsset in here)
Not sure why anyone would inline css, as in the future it's gonna be slower than external anyway (and currently doesn't make a big diff)

[akihikodaki]

I think it should be fine to just do it the same as vue without having the internal css parsing? What do you think? (removing CSSAsset in here)

I decided to use CSSAsset because Svelte lacks a feature to resolve something like url(./foo.png). It is too hard to implement with preprocess. (Indeed I have no idea other than adding more dirty hacks and boilerplate.) (UPDATE: of course I can change the behavior if you decide not to use it.)

Not sure why anyone would inline css, as in the future it's gonna be slower than external anyway (and currently doesn't make a big diff)

So you want compilerOptions.css to be false by default? I will make a change accordingly if so. (Note that setting false to compilerOptions.css will put CSS in a separate file.)

[DeMoorJasper]

@akihikodaki I only proposed that if it would get rid of CSSAsset if it doesn't than it doesn't really matter.

[akihikodaki]

@DeMoorJasper Well, I'm having a bit difficulty to understand your comment. You mean url(./foo.png) does not really matter and CSSAsset should be removed?

[DeMoorJasper]

Ow sorry, I meant if putting css in a seperate file gets rid of CSSAsset i would've preferred it, but apparently it doesn't so the default value doesn't really matter now.

Basically meaning leave the PR as is, unless u can fix the CSSAsset hack fix :)

[akihikodaki]

I understand. in the current implementation, CSSAsset is used only when putting CSS in a separate file, though it is always instantiated.

CSSAsset is used not because it is necessary to put in a separate file, but it is to transform:

.main {
  /* Reference an image file */
  background: url('./images/background.png');
  color: red;
}

(copied from https://parceljs.org)

So I'm wondering if you think this CSS should be supported.

[DeMoorJasper]

Yes it should, kinda surprised svelte doesn't automatically transform css requires into js requires if it inlines it.

I'll merge, possibly improve and release this soonish