cache does not work in watch mode

[akosyakov]

We are using code splitting in dev (watch) mode in order to avoid redownloading everything on page refresh but only changed bundles. But compression plugin keeps generating new compressed artifacts even for not changed bundles. I've tried to enable caching and it did not have any effect.

[akosyakov]

I see that record is found in the cache, but a new file is still emitted. So Express.js treats it as a new resource.

[alexander-akait]

Please create minimum reproducible test repo

[akosyakov]

@evilebottnawi Here you go: https://github.com/akosyakov/compression-webpack-with-watch

In order to reproduce:

• run yarn in order to install dependencies and start watching
• look at timestamps in lib folder for both bundles and gzipped archives
• wait sometime
• change client.js
• look at timestamps again, bundle.js is not changed, but gzipped is changed

Here is a Gitpod snapshot to reproduce:

[akosyakov]

@evilebottnawi does it look like an issue? Are you opened to a PR? What would be the proper solution? Skip emitting a new file if an original asset timestamp did not change?

[alexander-akait]

A lot of issues, you can debug it and send a PR, sorry

[ernestostifano]

For anyone getting here. A temporary solution, if writing a plugin is a possibility, is to collect and update effectively emitted assets paths on 'compiler.hooks.assetEmitted' hook and passing them to "compression-webpack-plugin" exclude option on each watch run. I'm currently doing that until this issue is fixed.

For additional information, please see this comment on relative PR.

[alexander-akait]

There are several solution:

• Implement on webpack side new API isAssetEmitted and skip files which already exists (ideally)
• Cache our compressed assets in memory between compilations, now the cache option only for filesystem cache (sounds like hacky)
• migrate on the assetEmitted hook (it can break assets manifest plugins)
• migrate on the optimizeAssets hook (ideally for webpack@6), the main problem - a lot of plugins uses emit hook for adding new assets, but it is wrong, on emit hook plugins should not adding new assets. I think we will throw a warning for webpack@5/webpack@6 if a plugin added assets into emit hook

[alexander-akait]

I need a little discussion with @sokra about it, in the near future I will find a solution, sorry for delay