Build: Improve how combined assets are generated

[gziolo]

Trac ticket: https://core.trac.wordpress.org/ticket/56615

It reverts the temporary workaround for the failing Test NPM CI check on Windows: https://core.trac.wordpress.org/changeset/54277.

It's based on the finding from @jsnajdr that stable hashes are only guaranteed for the production version of the build. In effect, I'm applying the following changes:

• generate combined asset files for both production and development
• store in the repository only the production version of the combined assets for packages, we use everything else only in development
• to make unit tests work, ensure that they ignore react fast refresh and use the production version of combined assets that are present in the source code

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[jsnajdr]

It's based on the finding from @jsnajdr that stable hashes are only guaranteed for the production version of the build.

I did some more debugging today and it seems that not even production build reliably guarantees stable order of modules and stable hashes. When the chunk modules are written to a file, they are ordered by module.identifier(), which is not the thing that you defined in optimization.moduleIds, e.g., named or deterministic, but the module's request field, which is the full absolute path to the module, like /Users/jsnajdr/project/src/index.js. See this webpack method that returns this.request and doesn't really look at anything else:

https://github.com/webpack/webpack/blob/9fcaa243573005d6fdece9a3f8d89a0e8b399613/lib/NormalModule.js#L338-L349

The real reason why production builds are OK is that production uses module concatenation. The offending date-fns modules are concatenated into another module and are no longer written separately. Then the unstable sorting doesn't happen.

I'll be investigating further in cooperation with @ockham

[gziolo]

I'll be investigating further in cooperation with @ockham

Thank you so much for sharing your findings. That would be great to confirm it won't cause similar issues in the future.

In the meantime, I applied all the necessary changes to make CI happy. I think it's a good improvement on its own as it allows us to keep only the file with combined assets for production to ensure that they never differ between platforms.

[ockham]

I'll be investigating further in cooperation with @ockham

Thank you so much for sharing your findings. That would be great to confirm it won't cause similar issues in the future.

Update: @jsnajdr prepared a minimal test case that I ran on Windows. He'll use the results to file a bug report against Webpack.

[ockham]

Thank you @gziolo! LGTM

[jsnajdr]

Webpack bug reported here: webpack/webpack#16289

[gziolo]

Committed with https://core.trac.wordpress.org/changeset/54289.