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yarn-plugin-backstage

packages/yarn-plugin/README.md

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yarn-plugin-backstage

This yarn plugin adds a backstage: version protocol to yarn, which replaces specific version ranges for @backstage/ packages. The only version range supported by this plugin is backstage:^, which has similar semantics to the corresponding workspace range when using workspace dependencies; locally, the package will always resolve to the exact version specified in the manifest for the Backstage release listed in backstage.json. If the dependent package is published, this version will be prefixed by ^.

Detailed instructions for using the plugin can be found in the docs.

Installation

bash
yarn plugin import https://versions.backstage.io/v1/tags/main/yarn-plugin

The resulting changes in the file system should be committed to your repo.

Usage

The yarn plugin recognizes the version string "backstage:^", and replaces it with the appropriate version based on the overall Backstage version in backstage.json.

Configuration

The plugin functionality can be configured with environment variables:

  • BACKSTAGE_VERSIONS_BASE_URL - The base URL for fetching the Backstage version manifest. Defaults to https://versions.backstage.io/v1/releases/VERSION/manifest.json. Useful for running the plugin in environment without direct access to the internet, for example by using a mirror of the versions API or a proxy. Note that the environment variable is just the host name, and the path is appended by the plugin.
  • BACKSTAGE_MANIFEST_FILE - Path to a local manifest file. If set, the plugin will not attempt to fetch the manifest from the network. Useful for running the plugin in environment without internet access and without mirror of the versions API.

Local Development

  • Run unit tests: yarn test
  • Build the plugin locally: yarn build
  • Rebuild whenever plugin files change: yarn start
  • Install local build (in a package directory outside the Backstage monorepo): yarn plugin import /path/to/backstage-repo/packages/yarn-plugin/bundles/@yarnpkg/plugin-backstage.js

The plugin can be manually tested in any repository running at least yarn 4.1.1. Sadly it can't be manually tested directly in the Backstage monorepo - since packages in this repository use workspace:^ dependencies, there's no use case for the yarn plugin.

Architecture

This section is intended for people working directly on this package. It describes the architecture of the plugin, and the means by which it manages npm package versions.

The Backstage yarn plugin operates on backstage:^ version ranges in package.json files using the following three components:

reduceDependency hook

Converts backstage:^ to backstage:^::backstage=1.34.0&npm=1.2.3

This hook is called by yarn when resolving direct and indirect dependencies in the workspace, and allows modifying the version range. The yarn plugin uses this hook to parameterize backstage:^ ranges with the current Backstage version and the corresponding npm package version from the manifest. This uses the system built into yarn for adding parameters to version ranges.

BackstageNpmResolver

Resolves the appropriate npm package for backstage:^ ranges and adds the npm range as a dependency

The BackstageNpmResolver ensures that the lockfile contains entries for both the backstage:^ range, and the corresponding npm:^<version> range. Including an entry for the backstage:^ range means that tools that reconcile the lockfile and package.json can match entries for Backstage packages together. Including an entry for the corresponding npm: range ensures that dependencies are not unlocked when switching between backstage:^ and npm: ranges in the lockfile, as happens when publishing the package or building a dist workspace using backstage-cli build-workspace.

beforeWorkspacePacking hook

Replaces backstage:^ ranges with the corresponding npm version ranges when packing packages for publishing

The yarn plugin is strictly optional, and intended to be opted-into in a specific Backstage repository. As such, when publishing packages, all backstage:^ versions should be removed from the package.json and replaced with the appropriate npm version ranges. This is handled by the beforeWorkspacePacking hook.

afterWorkspaceDependencyAddition hook

Replaces npm version ranges with backstage:^ ranges for @backstage/* dependencies added after the plugin has converted existing dependencies to backstage:^ range

afterWorkspaceDependencyReplacement hook

warns user with console message when running yarn add for a @backstage/* scoped dependency that is already a dependency in the target package. Doing so will remove the backstage:^ scope and replace it with the actual npm version range, which may not be desired.