Serialize generatedCode info to fix bug in asset module cache restoration

[ryanwilsonperkin]

What kind of change does this PR introduce?

Fixes #16160

A minimal reproduction of this bug is available at https://github.com/ryanwilsonperkin/webpack-16160

AssetGenerator calls out in a TODO-comment that the filename, assetInfo, and fullContentHash values must be captured in the 'data' object that's populated during code generation in order to be accessible in the AssetModulesPlugin. It notes that it must store them in the code generation results because it will be cached, but that appears to be incorrect as data is a simple Map that's instantiated within the NormalModule and not captured anywhere that would be cached.

As a result, configurations that use the asset/resource type and make changes to assets between cached builds will result in a runtime error as Webpack is able to access the file from cache but isn't able to access the expected values from the data object.

This solution captures the data object as a property of the NormalModule and hooks in to the existing serialize/deserialize functionality in order to make this value available across cached builds.

Did you add tests for your changes?

Not yet, I would appreciate support understanding what approach you've taken to testing this type of functionality so far.

Does this PR introduce a breaking change?

No

What needs to be documented once your changes are merged?

Shouldn't require documentation, fixing a low-level bug

[webpack-bot]

For maintainers only:

• This needs to be documented (issue in webpack/webpack.js.org will be filed when merged)
• This needs to be backported to webpack 4 (issue will be created when merged)

[alexander-akait]

Looks good, can you add test case, thank you

[ryanwilsonperkin]

Sure thing @alexander-akait , I've added a new test case now that mirrors the behaviour of the existing Compiler-caching.test.js approach. I've verified that this test fails on the main branch, and is fixed by the commits in this branch

[alexander-akait]

https://github.com/webpack/webpack/tree/main/test/watchCases/cache/asset-modules, so you don't need to write extra lines and it will be easy to maintance tests in future, thank you

[ryanwilsonperkin]

I originally attempted to write a test under asset-modules but could not get it to work, as far as I can see there isn't a mechanism in that test suite to give me the ability to modify an asset between compile steps. I had to heavily tweak the compilation approach in this unit test such that it:

• Used a new webpack() instance each time, to avoid relying on shared in-memory state
• Used a physical filesystem, so that cache could be written out and re-used between builds
• Made a deliberate modification to a source file between compile passes

I don't think these three things are possible under asset-modules

[alexander-akait]

@TheLarkInn Hello, can you review?

[TheLarkInn]

LGTM.

[TheLarkInn]

I had to confirm one detail about the type definition file not getting updated and that is because this._codeGeneratorData is using the underscore naming convention. Thank you so much @ryanwilsonperkin for the contribution. 🙏

[ryanwilsonperkin]

Thanks folks! Our team will be very happy to see this land :)

[TheLarkInn]

@ryanwilsonperkin assuming your team and a large piece of Shopify code is running on webpack v5, we are building a performance roadmap for v6/7 and if you have any performance analysis that you have ran against your builds that you are looking to see addressed, please feel free to reach out.

We're looking for at scale webpack builds to focus on for performance improvements.

[ryanwilsonperkin]

We'd certainly be interested, what would be the best way to coordinate with you?
I've recently been getting deeper into optimizing our webpack builds both for better chunking and for improved build speeds

[TheLarkInn]

1. I'll continue to look out for any perf bugs you submit
2. Let's continue conversations at webpack@opencollective.com, (cc selarkin@microsoft.com)
3. We have upcoming monthly roadmap rundown meetings. I'll take whatever email you send to me and add you to our roadmap meetings.