Nested package.json files break tree shaking

Intended outcome:

When I import from @apollo/client or any of its entrypoints (e.g. @apollo/client/react/hoc), Webpack should be able to correct tree-shake unused exports.

Actual outcome:

Webpack ends up including files that aren’t actually required by the imported values.

This occurs because Webpack uses the closest ancestor package.json to check for a "sideEffects" field to determine if tree-shaking is permissible. The root package.json in @apollo/client does correctly declare that only a single file in the package has side effects. However, before publishing, ./config/prepareDist.js creates additional, minimal package.json files for all of the various entrypoints that the package exposes. These package.json files do not have a "sideEffects" field, which means Webpack will refuse to perform tree shaking on them.

I can put together a reproduction if desired by the maintainers, but this is a pretty cut-and-dry bug, and the fix seems relatively straightforward: add "sideEffects" false to all nested package.json files. This will break down for the one entrypoint with a file that does have side effects, but I imagine this could either be hardcoded in https://github.com/apollographql/apollo-client/blob/main/config/entryPoints.js, or else done dynamically based the contents of the sideEffect field in the root package.json file.

Versions

  System:
    OS: macOS 10.15.7
  Binaries:
    Node: 14.15.4 - ~/.nvm/versions/node/v14.15.4/bin/node
    Yarn: 1.22.10 - ~/git/universal-roundup-client/node_modules/.bin/yarn
    npm: 6.14.10 - ~/.nvm/versions/node/v14.15.4/bin/npm
  Browsers:
    Chrome: 90.0.4430.93
    Edge: 90.0.818.56
    Firefox: 88.0
    Safari: 14.1
  npmPackages:
    @apollo/client: ^3.3.16 => 3.3.16 
    @apollo/react-testing: ^3.1.4 => 3.1.4

[nwalters512]

@nwalters512 Just released the changes from #8213 in @apollo/client@3.4.0-beta.26, if you want to check that out. 🙏

Looks great, thanks for the speedy fix! Excited to adopt this once 3.4.0 is released 🚀

[benjamn]

@nwalters512 Just published this in @apollo/client@3.3.18 as well, in case that’s an easier upgrade.