[Webpack 5] 3x slowdown caused by _discoverActiveExportsFromOtherStarExports

Bug report

What is the current behavior? Upgrading to Webpack 5 takes 5s to livereload my browser between changes: (the light green blocks at the bottom are calls to getStarReexports and the slow hotspot _discoverActiveExportsFromOtherStarExports) Webpack 4 takes 3s:

If the current behavior is a bug, please provide the steps to reproduce.

1. git clone -b feat/webpack-5 https://github.com/patternfly/patternfly-org && cd patternfly-org && yarn && yarn start
2. Wait ~1m for initial webpack compilation.
3. Save change to packages/v4/src/pages/home.js
4. Webpack 5 performs worse than Webpack 4, even with module: { unsafeCache: true } and eager-imports-webpack-plugin

798 assets
5779 modules
webpack 5.31.0 compiled successfully in 5051 ms

What is the expected behavior? Webpack 5 to be faster than webpack 4. Simply changing _discoverActiveExportsFromOtherStarExports to return new Map(); speeds Webpack up 3x:

798 assets
5779 modules
webpack 5.31.0 compiled successfully in 1475 ms

In 95% of cases developers aren’t touching star reexports.

I believe this is due to many included barrel files containing thousands of export * from './file';. Is there a way to speedup this _discoverActiveExportsFromOtherStarExports hotspot (or avoid it altogether) besides changing library code to export { list, of, named, exports } from './file';?

Other relevant information: webpack version: webpack@5.31.0 Node.js version: v14.16.0 Operating System: linux Relevant: #8644

[sokra]

I’m looking into fixing that slowness.

If you want an easy fix: 99% of that time is spend in a single file:

node_modules\@patternfly\react-icons\dist\esm\icons\index.js

In contains 1721 lines of export *. The file seem to be autogenerated. I guess it should be easy to generate normal reexports instead:

-export * from './accessible-icon-icon';
+export { AccessibleIconIcon } from './accessible-icon-icon';

export * complexity seem to be O(n²)… Each export * looks at the exports of all previous export *s.

And we haven’t implemented caching for exports that depend on other modules…

[Z-shh]

Thank you so much. Have an amazing day!

On Wed, Apr 14, 2021 at 8:00 AM zallen @.***> wrote:

Just changing the star exports in the autogenerated code reduced reload times down to 3s. I’m sure your optimizations will help even more. Thanks @sokra https://github.com/sokra !!

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