How to verify that webpack is using cache?

[gajus]

I've added configuration:

cache: {
  cacheDirectory: path.resolve(__dirname, '.webpack-cache'),
  type: 'filesystem',
},

I would expect subsequent builds to be faster, however, I am not seeing any change and there is nothing in the logs about using / not using cache. How to verify that cache is being used?

[vankop]

you can enable full log https://webpack.js.org/configuration/other-options/#infrastructurelogging

infrastructureLogging: { debug: true }

webpack should print logs like restore from cache..

[gajus]

Turns out I was right. For some reason cache is corrupted between builds.

[webpack-cli] Compiler starting... 
    [webpack-cli] Compiler is using config: '/home/github/actions-runner/_work/***/***/webpack.config.js'
<t> [webpack.cache.PackFileCacheStrategy] restore cache container: 93.550298 ms
    [webpack.cache.PackFileCacheStrategy/webpack.FileSystemInfo] /home/github/actions-runner/_work/***/***/webpack.config.js invalidated because hashes differ (9ede4d59ab03c8bf5d7001ae5869[105](https://github.com/contra/contra-web-app/runs/5483809008?check_suite_focus=true#step:17:105)6 != ff87b5ad91ed3854974913cc2f06f475)
    [webpack.cache.PackFileCacheStrategy] Restored pack from /home/github/actions-runner/_work/***/***/.webpack-cache/default-development.pack, but build dependencies have changed.
    [webpack.cache.PackFileCacheStrategy] resolving of build dependencies is invalid, will re-resolve build dependencies
<t> [webpack.cache.PackFileCacheStrategy] check build dependencies: 4858.754 ms
    [IdleFileCachePlugin] Initial cache was generated and cache will be persisted in 5s.
    [webpack-cli] Compiler finished
    [webpack.cache.PackFileCacheStrategy] Pack got invalid because of write to: ResolverCachePlugin|normal|dependencyType=|esm|path=|/home/github/actions-runner/_work/***/***|request=|/home/github/actions-runner/_work/***/***/server/template.html
    [webpack.cache.PackFileCacheStrategy] Storing pack...
    [webpack.cache.PackFileCacheStrategy] Capturing build dependencies... (/home/github/actions-runner/_work/***/***/webpack.config.js, /home/github/actions-runner/_work/***/***/node_modules/webpack/lib/, /home/github/actions-runner/_work/***/***/node_modules/file-loader/dist/cjs.js, /home/github/actions-runner/_work/***/***/node_modules/html-webpack-plugin/lib/loader.js, /home/github/actions-runner/_work/***/***/node_modules/babel-loader/lib/index.js, /home/github/actions-runner/_work/***/***/node_modules/style-loader/dist/cjs.js, /home/github/actions-runner/_work/***/***/node_modules/css-loader/dist/cjs.js, /home/github/actions-runner/_work/***/***/node_modules/url-loader/dist/cjs.js)
<t> [webpack.cache.PackFileCacheStrategy] resolve build dependencies: 6523.695669 ms
<t> [webpack.cache.PackFileCacheStrategy] snapshot build dependencies: 59.91588 ms
    [webpack.cache.PackFileCacheStrategy] Captured build dependencies
    [webpack.cache.PackFileCacheStrategy] 32002 fresh items in cache put into pack 0 (19187 items), 1 (12815 items)
<t> [webpack.cache.PackFileCacheStrategy] store pack: 29733.223749 ms
    [webpack.cache.PackFileCacheStrategy] Stored pack (32002 items, 2 files, 2562 MiB)

At least now I know what to debug further. Thank you.

[vankop]

which webpack version are you using? ( there was some cache invalidation fixes in several last minor releases )

otherwise will be great if you reduce this to reproducible repo. (maybe reduce to particular module request /_work/***/***/server/template.html )

[gajus]

The latest. It is this issue #10400

[gajus]

It is not clear from these logs if cache is being used:

    [webpack-cli] Compiler starting... 
    [webpack-cli] Compiler is using config: '/home/github/actions-runner/_work/***/***/webpack.config.js'
<t> [webpack.cache.PackFileCacheStrategy] restore cache container: 203.660013 ms
<t> [webpack.cache.PackFileCacheStrategy] check build dependencies: 146.646929 ms
<t> [webpack.cache.PackFileCacheStrategy] restore cache content metadata: 135.792899 ms
    [webpack.cache.PackFileCacheStrategy] starting to restore cache content 0 (75.8 MiB) because of request to: ResolverCachePlugin|normal|dependencyType=|esm|path=|/home/github/actions-runner/_work/***/***|request=|/home/github/actions-runner/_work/***/***/src/index
<t> [webpack.cache.PackFileCacheStrategy] restore cache content 0 (75.8 MiB): 883.9945 ms
    [webpack.cache.PackFileCacheStrategy] starting to restore cache content 1 (2.4 GiB) because of request to: ResolverCachePlugin|normal|dependencyType=|esm|path=|/home/github/actions-runner/_work/***/***/node_modules/relay-sentry/node_modules/@sentry/utils/esm|request=|tslib
<t> [webpack.cache.PackFileCacheStrategy] restore cache content 1 (2.4 GiB): 6049.024799 ms
    [IdleFileCachePlugin] Initial cache was generated and cache will be persisted in 5s.
    [webpack-cli] Compiler finished
    [webpack.cache.PackFileCacheStrategy] Pack got invalid because of write to: ResolverCachePlugin|loader|path=|/home/github/actions-runner/_work/***/***|request=|/home/github/actions-runner/_work/***/***/node_modules/file-loader/dist/cjs.js
    [webpack.cache.PackFileCacheStrategy] Storing pack...
    [webpack.cache.PackFileCacheStrategy] 12458 fresh items in cache put into pack 2 (6601 items), 3 (5458 items), 4 (399 items)
    [webpack.cache.PackFileCacheStrategy] Split pack 0 into pack 0 with 6090 used items and pack 5 with 6 unused items
<t> [webpack.cache.PackFileCacheStrategy] store pack: 17807.692653 ms
    [webpack.cache.PackFileCacheStrategy] Stored pack (32007 items, 6 files, 2537 MiB)

It appears as if Pack got invalid because of write to line would indicate that cache is invalid and therefore not being used.

Though I am not clear as to what is the reason for it.