Avoid dynamic facade chunks

[lukastaegert]

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 #3125

Description

This will prevent the creation of facade chunks for dynamic imports to reduce the number of chunks. Previously, especially for more complex bundles, most dynamic imports would create an additional chunk that just contained re-exports to create the correct namespace for the import.

With this PR, this will no longer happen:

• if the imported chunk itself does not export anything that is not part of the namespace, it will become the facade chunk (this was already the old logic)
• if an entry point has a facade chunk due to preserveEntrySignatures: 'strict', this one will be used by the import (this was already the old logic as well)
• otherwise, a dynamic namespace object will be created inside the chunk and exported as a named export, then it will be unwrapped by the importing chunk:
  • output with this PR
  • output in v2.7.6

I think this will a huge improvement to the chunking experience.

Additionally, this will also change the code generated for CommonJS dynamic imports from (REPL)

new Promise(function (resolve) { resolve(require('./dynamic.js')); });

to (REPL)

Promise.resolve().then(function () { return require('./dynamic.js'); });

This will fix a bug where the contents of the imported file are executed synchronously before the current synchronous block has finished executing. This could cause nasty issues when a dynamic import directly requires the currently executing file.

[rollup-bot]

Thank you for your contribution! ❤️

You can try out this pull request locally by installing Rollup via

npm install rollup/rollup#avoid-dynamic-facades

or load it into the REPL:
https://rollupjs.org/repl/?circleci=10804

[codecov]

Codecov Report

Merging #3535 into master will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #3535      +/-   ##
==========================================
+ Coverage   96.22%   96.24%   +0.01%     
==========================================
  Files         176      176              
  Lines        5984     6014      +30     
  Branches     1765     1773       +8     
==========================================
+ Hits         5758     5788      +30     
  Misses        112      112              
  Partials      114      114              

Impacted Files	Coverage Δ
src/ast/variables/Variable.ts	100.00% <ø> (ø)
src/rollup/rollup.ts	100.00% <ø> (ø)
src/Chunk.ts	99.78% <100.00%> (+0.01%)	⬆️
src/Module.ts	98.89% <100.00%> (-0.02%)	⬇️
src/ast/nodes/ImportExpression.ts	100.00% <100.00%> (ø)
src/ast/variables/NamespaceVariable.ts	100.00% <100.00%> (ø)
src/utils/deconflictChunk.ts	100.00% <100.00%> (ø)

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[lukastaegert]

This is ready to be merged now