[Bug]: Can not read loaderContext.data when using pitch loader

[chenjiahan]

System Info

System:
OS: macOS 13.6.6
CPU: (10) arm64 Apple M1 Pro
Memory: 2.56 GB / 32.00 GB
Shell: 5.9 - /bin/zsh
Binaries:
Yarn: 1.22.19 - ~/Library/Application Support/fnm/node-versions/v18.19.0/installation/bin/yarn
npm: 10.2.3 - ~/Library/Application Support/fnm/node-versions/v18.19.0/installation/bin/npm
pnpm: 7.18.1 - ~/Library/Application Support/fnm/node-versions/v18.19.0/installation/bin/pnpm
bun: 1.0.30 - ~/.bun/bin/bun
Browsers:
Chrome: 124.0.6367.119
Safari: 16.6
npmPackages:
@rspack/cli: ^0.6.3 => 0.6.3
@rspack/core: ^0.6.3 => 0.6.3

Details

Can not read loaderContext.data when using pitch loader.

For example, create a simple pitch loader and set loaderContext.data:

module.exports = function (code) {
  console.log("this.data", this.data);
  return code;
};

module.exports.pitch = function (_a, _b, data) {
  data.foo = "bar";
};

• Webpack:

• Rspack:

This seems to be a problem with the execution order of the pitch loaders in Rspack, causing data to not be set to the correct loader object.

Reproduce link

https://github.com/chenjiahan/rspack-repro-pitch-loader-data

Reproduce Steps

1. pnpm i
2. pnpm build:webpack
3. pnpm build:rspack

[h-a-n-a]

This is highly related with the current loader impl.

Normally, webpack loaders, in a single loader pipeline, share the same loader context with loaders in both pitching and normal stage. That is said the LoaderContext["data"] is shared as well. In rspack, after the pitching loader, the JavaScript loader runner will yield and give control back to Rust loader runner to load resources (loader runner's process_resource hook). This results in the data being lost.

[chenjiahan]

Get it 👍

I found this issue when using the cache-loader, it is not urgent. If we can solve this issue, Rspack users can use cache-loader to speed up rebuild, which will be a practical approach before we support portable cache.

[h-a-n-a]

Yes, we have to resolve this issue. Roughly speaking, the rust LoaderItem(i.e. the LoaderObject counterpart in webpack) is immutable. To make it work with LoaderContext["data"], we need to change it to mutable and pass loader object with data instead of passing loader identifiers (upon which we create LoaderObject in loader runner on JS side) to JS to solve this issue.

[CPunisher]

This also needs to dynamically add fields on data. Maybe we can refer to #6631 's implementation of saving data only on the js side?