feat: async modules / top level await #5450

ForsakenHarmony · 2023-07-03T21:10:32Z

Description

For now this is just for top level await, in the future we want to be able to support external esm modules

Testing Instructions

vercel · 2023-07-03T21:10:41Z

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crates/turbopack-ecmascript-runtime/js/src/shared/runtime-utils.ts

github-actions · 2023-07-03T21:15:06Z

✅ This change can build next-swc

github-actions · 2023-07-03T21:34:12Z

⚠️ CI failed ⚠️

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Turbopack Rust tests (mac/win, non-blocking)

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sokra

Looks good in general.

I'm not sure if this hangs when there are cycles in the module graph... need to verify, maybe with a test

It would also be great to have some tests that actually evaluate the code. Wills PR would help here

crates/turbopack-ecmascript-runtime/js/src/shared/runtime-utils.ts

sokra · 2023-07-05T14:54:46Z

crates/turbopack-ecmascript/src/analyzer/top_level_await.rs

    let mut visitor = TopLevelAwaitVisitor::default();

    m.visit_with(&mut visitor);

-    visitor.has_top_level_await
+    visitor.top_level_await_span
 }

 #[derive(Default)]
 struct TopLevelAwaitVisitor {


It might be possible to merge this visitor into detect_dynamic_export to avoid walking the ast multiple times

sokra

Ok there are a bunch of new interactions that didn't exist with webpack.

We expose 2 types of exports module.exports (used for require) and module.namespaceObject (use for import)
For an non-ESM (where module.namespaceObject doesn't exist), we use interopEsm to create a interop namespace object.
For ESM module.exports and module.namespaceObject must be equal
We need to proxify the exports for dynamicExport. (Both module.exports and module.namespaceObject)
We need to promisify the exports for async modules.
and 5. are quite new.

First thing: It seems like dynamicExport is a bit wrong (even on main) as it doesn't proxify module.exports. We need to add that.

Second thing: When combining 4. and 5. we need to proxify the resolved value of the promise. But we also don't want to change the Promise instance since it could already be imported (and awaited) by some other modules.

So we want to be able to change the resolved value.

So the dynamicImport method probably wants to detect async modules and modify the module.namespaceObject[turbopackExports] value. And the async modules implementation wants to avoid using it's local scoped exports object and instead resolve to the current value of promise[turbopackExports], which might be proxified.

crates/turbopack-ecmascript-runtime/js/src/shared/runtime-utils.ts

github-actions · 2023-07-20T14:57:36Z

Linux Benchmark for 945ba0b

Click to view benchmark

Test	Base	PR	%
bench_hmr_to_commit/Turbopack CSR/1000 modules	7588.84µs ± 24.87µs	7488.74µs ± 42.07µs	-1.32%
bench_hmr_to_eval/Turbopack CSR/1000 modules	6842.72µs ± 15.45µs	6927.77µs ± 75.00µs	+1.24%
bench_startup/Turbopack CSR/1000 modules	871.09ms ± 5.06ms	863.18ms ± 4.54ms	-0.91%

sokra

I'll merge it, but there are some outstanding follow-up tasks:

Add documentation to all public items. Especially in the async_module.rs file. Mention what Scc stands for or maybe even write out the full name.
Add a test case of circular dependency graphs.

* vercel/turborepo#5567  * vercel/turborepo#5576  * vercel/turborepo#5503  * vercel/turborepo#5487  * vercel/turborepo#5488  * vercel/turborepo#5450  --------- Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

### Description For now this is just for top level await, in the future we want to be able to support external esm modules ### Testing Instructions Closes WEB-434 Closes WEB-987

ForsakenHarmony requested a review from a team as a code owner July 3, 2023 21:10

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ForsakenHarmony added 2 commits July 20, 2023 15:37

simplify dynamicExport

a4a0e21

unsimplify dynamicExport

5556ebd

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glob fixes, though it seems it's fully recursive

732dd01

ForsakenHarmony requested a review from sokra July 20, 2023 15:31

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sokra merged commit fc4cfaa into main Jul 21, 2023

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sokra mentioned this pull request Jul 21, 2023

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feat: async modules / top level await #5450

feat: async modules / top level await #5450

ForsakenHarmony commented Jul 3, 2023

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feat: async modules / top level await #5450

feat: async modules / top level await #5450

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ForsakenHarmony commented Jul 3, 2023

Description

Testing Instructions

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⚠️ CI failed ⚠️

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Linux Benchmark for 945ba0b

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