Add backstage field to export in package.json

[HHogg]

This adds a step to the prepack command that will add an additional "backstage" metadata field to exports which provides information on the default export of the Backstage package.

{ 
  "exports": {
    ".": {
      "require": "./dist/index.cjs.js",
      "types": "./dist/index.d.ts",
      "default": "./dist/index.cjs.js"
    },
    "./alpha": {
      "require": "./dist/alpha.cjs.js",
      "types": "./dist/alpha.d.ts",
      "default": "./dist/alpha.cjs.js",
      "backstage": "@backstage/BackendFeature" <------ New field
    },
    "./package.json": "./package.json"
  },
}

The way it extracts the information is to use ts-morph which works the same way as the typescript server does for IDEs and uses the compiler to build up references and resolves types so we can avoid having to traverse the AST to look for type information.

[backstage-goalie]

Changed Packages

Package Name	Package Path	Changeset Bump	Current Version
@backstage/cli	packages/cli	patch	v0.27.1

[backstage-goalie]

Thanks for the contribution!
All commits need to be DCO signed before they are reviewed. Please refer to the the DCO section in CONTRIBUTING.md or the DCO status for more info.

[Rugvip]

Nice, I think we're about ready to ship 😎

Just a couple of minor bits

[Rugvip]

Nice, let's ! 👍

Love how slim we ended up getting this in the end 🎉

[github-actions]

Thank you for contributing to Backstage! The changes in this pull request will be part of the 1.32.0 release, scheduled for Tue, 15 Oct 2024.