await-then-catch

[Rich-Harris]

Ref #654. So far, this just teaches the parser how to deal with {{#await ...}} and friends.

[codecov-io]

Codecov Report

Merging #952 into master will increase coverage by 0.05%.
The diff coverage is 91.54%.

@@            Coverage Diff             @@
##           master     #952      +/-   ##
==========================================
+ Coverage   91.78%   91.84%   +0.05%     
==========================================
  Files         110      112       +2     
  Lines        3980     4107     +127     
  Branches     1304     1332      +28     
==========================================
+ Hits         3653     3772     +119     
- Misses        142      143       +1     
- Partials      185      192       +7

Impacted Files	Coverage Δ
...generators/server-side-rendering/visitors/index.ts	100% <ø> (ø)	⬆️
test/parser/index.js	100% <ø> (ø)	⬆️
src/generators/dom/visitors/index.ts	100% <ø> (ø)	⬆️
src/generators/server-side-rendering/preprocess.ts	100% <100%> (ø)	⬆️
src/generators/dom/preprocess.ts	97.68% <100%> (+0.23%)	⬆️
...ators/server-side-rendering/visitors/AwaitBlock.ts	100% <100%> (ø)
src/parse/index.ts	89.28% <100%> (+0.82%)	⬆️
src/generators/Generator.ts	94.03% <100%> (+0.1%)	⬆️
src/generators/server-side-rendering/index.ts	98.07% <100%> (+0.07%)	⬆️
src/parse/state/mustache.ts	88.88% <86.36%> (+0.98%)	⬆️
... and 3 more

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[Rich-Harris]

I think this is just about ready, if anyone is curious to take a look. There's room for improvements — some opportunities for DRYing out, etc — but the functionality is there.

Not covered in this PR:

• await once
• transitions (would be nice to e.g. fade from loading to rendered states)
• {{#await promise then value}} shorthand
• async/streaming SSR renderer

[aubergene]

Tried to read the code, but I don't know the innards of Svelte well enough. I'm using this branch and it works as expected and is super helpful! Merge ASAP :)

Edit: I found I got these errors when trying to use two await blocks within the same component

shared.js:21 Uncaught DOMException: Failed to execute 'insertBefore' on 'Node': The node before which the new node is to be inserted is not a child of this node.
    at insertNode (http://localhost:3000/public/js/test.js:26:9)
    at Object.mount [as m] (http://localhost:3000/public/js/test.js:399:4)
    at Object.mount [as m] (http://localhost:3000/public/js/test.js:337:18)
    at new Test (http://localhost:3000/public/js/test.js:573:18)
    at http://localhost:3000/public/test.html:18:14
insertNode @ shared.js:21
mount @ Test.html:14
mount @ Test.html:4
Test @ Test.html:19
(anonymous) @ test.html:18
Test.html:32 GET http://localhost:3000/now/ 404 (Not Found)
nowFetch @ Test.html:32
_recompute @ Test.html:19
Test @ Test.html:19
(anonymous) @ test.html:18
Test.html:33 GET http://localhost:3000/every10/ 404 (Not Found)
every10Fetch @ Test.html:33
_recompute @ Test.html:19
Test @ Test.html:19
(anonymous) @ test.html:18
shared.js:25 Uncaught (in promise) TypeError: Cannot read property 'removeChild' of null
    at detachNode (shared.js:25)
    at Object.unmount [as u] (Test.html:11)
    at replace_await_block_1 (Test.html:6)
    at Test.html:6
    at <anonymous>

[Rich-Harris]

Good catch, thanks — it was using the wrong variable to use when mounting, which meant it tried to attach itself to a not-yet-existent DOM node