Plugin should update `contenthash` after minification

[jakub-g]

This is a behavior that was probably in place forever with uglify hence it remains with terser as well.

versions

• webpack Version: 4.20.1
• terser-webpack-plugin Version: 1.1.0

config

    output: {
        filename = 'myprefix.[name].[contenthash].js',
        chunkFilename = 'myprefix.[name].[contenthash].js'
    },
    optimization: {
-       minimize: false,
+       minimize: true,
        minimizer: [new TerserPlugin()],
    }

Expected Behavior

• When minification is on, contenthash of the output files should be different compared to when it is off

Actual Behavior

• Regardless if minification is on or off, same contenthash is generated. i.e. file names are the same

This is problematic in case of scenario of upgrading the minificator.

• Since minification has no impact on the final file name, minifying with plugin version N vs plugin version N+1 might yield different content out of the same input file, yet same file name.
• Problematic in scope of long term caching, particularly in case of a bug in minificator. This can yield weird problems in deployment pipelines, CDNs etc. or lead to situation where different users have file with same name but different contents, depending on when they access the files and how the caching headers are configured.

To sum up, hard to diagnose bugs can happen if you're not aware of this issue.

According to webpack/webpack#7483 (comment)

plugin should regenerate contenthash if they change content of file

[alexander-akait]

@jakub-g sounds interesting, can you provide minimum reproducible repo where contenthash is same for difference content, maybe bug in webpack

[michael-ciniawsky]

+ minimize: true

Don't do that as this will add the uglifyjs-webpack-plugin (default) to plugins behind the scenes (webpack =< v4.0.0), it's either minimize or minimizer: [ ...plugins ]

terser-webpack-plugin reuses the (original) asset filename, so content changes aren't reflected in the hash portion of the filename at all atm. Not sure if tapping into the related contentHash hooks provided by webpack would work as a solution here (but maybe)

[dreyks]

@michael-ciniawsky yes plugin should tap into compilation.hooks.contentHash.tap to update the hash

[michael-ciniawsky]

Did you try this? According to https://github.com/webpack/webpack/blob/master/lib/Compilation.js#L319 it get the chunk passed as an argument which is should already be rendered when the terser-webpack-plugin is applied

[alexander-akait]

@dreyks friendly ping

[dreyks]

ugh... no spare time currently sorry

[edmorley]

In addition to the use-case above of upgrading minifier version to fix a minification bug, this issue also affects changing minification options. eg: adjust terserOptions and the generated contenthash stays the same.

[alexander-akait]

Right now, it is impossible change contenthash based on minified output (because when we optimize files, we already have assets like my.1a2b3c.js where 1a2b3c is content hash), i think we can fix it in webpack@5 (need internal refactor). But we can update hash based on minified version and ``minified` options, ti should solve problem partially

[alexander-akait]

Partial fixed #44, let's leave the problem open because we need regerate contenthash based on minified output, it is require some change in webpack. Now we regenerate contenthash when terser was updated or terserOptions was changed.

[jakub-g]

@evilebottnawi thanks for picking this, I updated the plugin to 1.2.1 and indeed it solves the cases you mentioned.

Should I open a linked ticket on a webpack repo for the refactor needed to have the full proper fix?

[alexander-akait]

@jakub-g it is already in todo, maybe we solve this problem for webpack@5 👍