feat: tree-shake deterministic dynamic imports

[antfu]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:

resolves #4951

fix #3417
fix #3447

Description

Full proposal in #4951

This PR enables tree-shaking for deterministic dynamic imports. The following are valid cases:

const { foo } = await import('foo')

(await import('foo')).foo

import('bar').then(({ foo }) => {})

Idea credits to:

• webpack: support destructuring assignment with AwaitExpression webpack/webpack#16995
• Parcel: https://parceljs.org/features/scope-hoisting/#dynamic-imports

[vercel]

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Name	Status	Preview	Comments	Updated (UTC)
rollup	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Apr 23, 2023 7:23pm

[codecov]

Codecov Report

Merging #4952 (7a0ab4c) into master (5af8799) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #4952   +/-   ##
=======================================
  Coverage   98.98%   98.98%           
=======================================
  Files         222      222           
  Lines        8050     8112   +62     
  Branches     2210     2236   +26     
=======================================
+ Hits         7968     8030   +62     
  Misses         28       28           
  Partials       54       54           

Impacted Files	Coverage Δ
src/Module.ts	100.00% <100.00%> (ø)
src/ast/nodes/ImportExpression.ts	100.00% <100.00%> (ø)
src/ast/variables/NamespaceVariable.ts	100.00% <100.00%> (ø)

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[lukastaegert]

Just some final comments and a possible optimization I stumbled upon.

[lukastaegert]

Perfect, thanks a lot!

[rollup-bot]

This PR has been released as part of rollup@3.21.0. You can test it via npm install rollup.

[dasa]

Should this be doc'ed here too? https://rollupjs.org/introduction/#tree-shaking

[lukastaegert]

Any PR for the docs is welcome! I guess something similar to what Parcel has does not hurt.

[dasa]

Is this what you're referring to? https://parceljs.org/features/scope-hoisting/#dynamic-imports

[lukastaegert]

👍
And we might even include a REPL link to see it in action and play around