Swift 5.5 Package Collections

Currently, it can be difficult to discover packages that fit particular use cases. There is also no standardized way of accessing metadata about a package which is not part of the package manifest itself.

Introduction

We believe there are three different components in the space of package discovery with different purposes:

Package Registry is focused on hosting and serving package sources as an alternative to fetching them directly from git. The goal is to provide better immutability, durability and potentially improve performance and security. This initiative is in-progress and governed by a separate proposal.

Package Index is focused for providing a search index for packages. The goal is to improve discoverability of packages that may be hosted anywhere, and provide a rich set of metadata that helps making informed decisions when choosing dependencies. The Index indexes the package core metadata available in Package.swift as well as additional metadata from additional and external sources. An example of a package index is https://swiftpackageindex.com.

Package Collections which are the subject of this proposal are closer to the Package Index than to the Package Registry. Collections are also designed to make discovery easier, but focused on simpler curation lists that can be easily shared rather than on larger scale indexing and ranking system that requires infrastructure. This design is the first step in teaching SwiftPM about discovery of packages and future work to support Package Indexes can build on this initial design.

Motivation

Currently, it can be difficult to discover packages that fit particular use cases. There is also no standardized way of accessing metadata about a package which is not part of the package manifest itself. We envision educators and community influencers publishing package collections to go along with course materials or blog posts, removing the friction of using packages for the first time and the cognitive overload of deciding which packages are useful for a particular task. We also envision enterprises using collections to narrow the decision space for their internal engineering teams, focusing them on a trusted set of vetted packages.

Exposing the data of package collections via libSwiftPM and the swift package-collection command-line interface will also allow other tools to leverage this information and provide a richer experience for package discovery that is configured by the user in one central place.

Proposed solution

We propose to introduce a new concept called Package Collections to the Swift package ecosystem. Collections are authored as static JSON documents and contain a list of packages and additional metadata per package. They are published to a web server or CDN-like infrastructure making them accessible to users. SwiftPM will gain new command-line interface for adding and removing collections and will index them in the background, allowing users to more easily discover and integrate packages that are included in the collections.

For example, a course instructor knows they intend to teach with a set of several packages for their class. They can construct a collection JSON file, representing those packages. Then, they can post that JSON file to a GitHub repo or a website, giving the URL to that JSON file to all their students. Students use SwiftPM to add the instructor's collection to their SwiftPM configuration, and any packages the instructor puts into that collection can be easily used by the students.

Detailed design

We propose to add a new sets of commands under a swift package-collection command-line interface that support the following workflows:

Managing collections
Querying metadata for individual packages
Searching for packages and modules across collections

We also propose adding a new per-user SwiftPM configuration file which will initially store the list of collections a user has configured, but can later be used for other per-user configuration for SwiftPM.