config/: Shared configuration files for tools like TypeScript, ESLint, and Jest.packages/: Libraries under this monorepo, can be private or publishable.apps/: Applications, such as web apps, mobile apps, or server-side apps.
To eliminate the need to maintain multiple copies of the same configurations, define the same dependencies across different packages, and still allow for package-specific overrides, we package the shared configurations into extendable packages to be installed and used by the packages needing them.
Note that for executables such as tsc, eslint, and jest to be accessible from each workspace that uses the shared TypeScript, ESLint, and Jest configurations, those workspaces should explicitly install such tools rather than relying on the shared configurations' dependencies. Therefore, the shared configurations will only list such dependencies as "peerDependencies". The consistencies of those config-packages-defined "peerDependencies" can be automatically updated by running yarn constraints --fix.
The @rnstudy/eslint-config package is installed at the root of the monorepo to lint top-level configuration files (such as yarn.config.cjs) and to force hoisting of the ESLint configs and plugins used in @rnstudy/eslint-config, ensuring their accessibility and not to be installed nested in the eslint-config package - where ESLint would not be able to find them.
Normally, when we install and import a package from another package in the monorepo, due to the entry point defined in the package.json of the imported package, what we are importing is the compiled code (e.g., dist/), but not the source code (e.g., src/). This means that we need to recompile the imported package every time we make a change to it, which is not very convenient for development. Also, the "Go to Definition" feature of IDEs might not be as convenient as will be taking us to the compiled definitions instead of the definitions in the source code.
As a workaround, we can leverage TypeScript's paths compiler option in the tsconfig.json of the importing package to map the import path to the source code of the imported package. This way, we can switch to importing the source code instead of the compiled code during development without changing the import paths in the source code of the importing package. This is especially useful when we are working on both the importing and imported packages at the same time.
See the tsconfig.json files of packages/plus-two and apps/sample-app for examples.
Note
Defining the paths compiler option will not change how import paths are emitted, while this is the desired behavior for building the package for distribution, but you will need to make sure you have also handled the mappings while using other tools such as Jest, ts-node or Babel.
For Jest, it will be done automatically by using the jestBaseConfig function provided by @rnstudy/jest-config.
As for ts-node, it can be done by using the tsconfig-paths package, see the tsconfig.json file in apps/sample-app for an example.