Augmented chunk hashes based on imported css code

[dionysiusmarquis]

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• [x] It's really useful if your PR references an issue where it is discussed ahead of time. In many cases, features are absent for a reason. For large changes, please create an RFC: https://github.com/sveltejs/rfcs
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• [ ] Ideally, include a test that fails without this PR but passes with it.

Tests

• [ ] Run the tests with npm test and lint the project with npm run lint

Fixes: #1660

Currently the chunk hashes don't include "injected" css code coming from script css imports. This is because the injection is happening in bundle hooks and at this stage all depending chunk imports will already be resolved using hashes that don't "react" to css changes. This is especially crucial in caching environments. To ensure that the chunk hashes also change as soon as imported css gets updated this PR adds a css_hashing plugin to the rollup compiler. The augmentChunkHash hook is utilised to provide a hash based on all imported css codes.

[benmccann]

It looks like this will need to be rebased. I sent a small PR in https://github.com/sveltejs/sapper/pull/1677 and didn't realize it would conflict with this

[dionysiusmarquis]

@benmccann This approach doesn't work anymore, since the update of rollup-plugin-css-chunks (https://github.com/sveltejs/sapper/commit/8a2769da8ed95c3daacfadb645946fc9822be4b1#diff-7ae45ad102eab3b6d7e7896acd08c427a9b25b346470d7bc6507b6481575d519R63).

That's because the css files won't be present in thechunk.modules anymore. This is most likely because of this change: https://github.com/domingues/rollup-plugin-css-chunks/commit/3632de47adea7a0447e0d53b0a608cecac1307c8#diff-dcdc3e0b3362edb8fec2a51d3fa51f8fb8af8f70247e06d9887fa934834c9122L90

Following: https://github.com/rollup/rollup/issues/3655

[dionysiusmarquis]

@benmccann Ok, I rebased and updated the approach. Maybe you could have another look. I had to add moduleSideEffects: 'no-treeshake'. I was also able to simplify the augmentChunkHash part because I had to determine is_svelte_css in transform already.

[benmccann]

It looks like there's a merge conflict here. This one was pretty complicated to understand and test. I wonder if it might be better to just make sure this works as intended in SvelteKit instead? SvelteKit uses Vite for CSS bundling which is a completely different set of code, so there's a good chance this issue doesn't exist there

[dionysiusmarquis]

Everything is working as expected in SvelteKit, I'd say. Running dev imported css inside <script> will be added "unbundled" as inline css. build will put them in the corresponding bundled css, correctly hashed.

[benmccann]

SvelteKit 1.0 is now out and Sapper is deprecated, so I'm going to close this