Webpack v5.99.9 production build failing to load a Vue 2 application

[woahitsjc]

Upgrading webpack to v5.99.9 or above causes the production build to fail at runtime:

Packages:
webpack: 5.102.0
vue: 2.7.16
typescript: 5.8.3
mini-css-extract-plugin: 2.9.4 (relevant to production config)
vuex: 3.6.2

Webpack configuration differences between development and production:

{
    ...rest,
    devtool: mode === "production" ? undefined : "eval-source-map",
    plugins: [
        new webpack.DefinePlugin({
            // This is used for VueX
            PRODUCTION: JSON.stringify(mode === "production")
        }),
        new MiniCssExtractPlugin({
            filename: mode === "production" ? "[name].[contenthash].bundle.css" : "[name].dev.bundle.css",
        })
    ],
    output: {
        publicPath: "",
        path: path.join(__dirname, <path-to-wwwroot-folder>),
        filename: mode === "production" ? "[name].[contenthash].bundle.js" : "[name].dev.bundle.js",
        devtoolModuleFilenameTemplate: info => {
            let $filename = "sources://" + info.resourcePath;
            if (info.resourcePath.match(/\.vue$/) && !info.query.match(/type=script/)) {
                $filename = "webpack-generated:///" + info.resourcePath + "?" + info.hash;
            }
            return $filename;
        },
        devtoolFallbackModuleFilenameTemplate: "webpack:///[resource-path]?[hash]"
    },
    resolve: {
        alias: {
            "vue": mode === "production" ? "vue/dist/vue.min.js" : "vue/dist/vue.js",
            "@common": path.resolve(__dirname, "./src/common/"),
            "@css": path.resolve(__dirname, "./styles"),
        },
        extensions: [".ts", ".tsx", ".js", ".vue"]
    },
}

[alexander-akait]

Unfortunately there is not enough information to help you, try to make a reproducible repository. Does this only happen in production? Can you try to disable minimizer (set optimizations.minimize: false) and look at result?

[Jameskmonger]

Hi @alexander-akait thanks for your response.

We're not able to create a reproducible repository at the moment, it doesn't seem to occur in a more simple setup.

I have identified that the issue seems to relate to the usedExports flag. As @woahitsjc mentioned, this occurs in 5.99.9 onwards and only when building with production mode.

Without specifying a value for usedExports, a number of exports from a number of modules are removed, causing runtime breakages. With the flag set to false explicitly the build now succeeds in 5.99.9.

[alexander-akait]

@Jameskmonger Thanks for details, looks like a bug/regression, did you try the latest version 5.102.0? Also can you try to disable optimizations.minimize: false to see the code where it happens, it may help to identify the problem place/pattern, without real code hard to say where and why it happens, we have a a lot of tests for used exports, anyway looks like we didn't cover your case, waiting feedback