The design misalignments between Rspack and webpack

[hardfist]

This discussion channel is used to track the design(not implmentation) misalignments between Rspack and webpack, we need to align with webpack unless we have strong solid reason to diff with webpack.

[hardfist]

defaultValue of optimization.removeAvailableModules is set true in Rspack https://github.com/web-infra-dev/rspack/blob/main/packages/rspack/src/config/defaults.ts#L712 but set false in webpack.

[JSerFeng]

Webpack can remove available duplicate modules, it achieve this using code splitting, and RemoveParentModules, the optimization.removeAvailableModules config only disable the latter, so the optimization from code splitting, it's still enabled.
So for Webpack whether disable optimization.removeAvailableModules or not, available duplicate modules will be removed eventually, so Rspack enables it by default, and if you don't want this optimization, you can turn it off.

[LingyuCoder]

compilation.hooks.runtimeModule is different with webpack.

In Webpack, plugin can get the module instance directly through compilation.hooks.runtimeModule, and then modify its content by overriding its getGenerateCode() method like below:

compilation.hooks.runtimeModule.tap('xxx', (module, chunk) => {
    if (chunk.name === 'xxx' && (module.name === 'xxx' || module.constructor.name === 'xxx')) {
        const originSource = module.getGeneratedCode();
        const appendSource = "/* new source */";
        module.getGeneratedCode = () => `${originSource}\n${appendSource}`;
    }
});

But in Rspack, since the injection of the runtime module is on the Rust side, and it is very hard to port the entire runtime module + runtime requirements to the JavaScript side.
So it is necessary to convert the Rust-side runtime module into a JsModule, transmit it to the JavaScript side for modification, and then send it back to the Rust side.
Therefore, the modification of the runtime module is based on string transmission, and it cannot be as flexible as Webpack, only supporting the replacement of module source:

compilation.hooks.runtimeModule.tap("TestFakePlugin", (module, chunk) => {
    if (chunk.name === 'xxx' && (module.name === 'xxx' || module.constructorName === 'xxx')) {
        const originSource = module.source.source.toString('utf-8');
        const appendSource = "blabla";
        module.source.source = Buffer.from(
            `${originSource}\n${appendSource}`,
            "utf-8"
        );
    }
});