SE-0201: Package Manager Local Dependencies

Introduction

This proposal adds a new API in PackageDescription to support declaring dependency on a package using its path on disk instead of the git URL.

Motivation

There are two primary motivations for this proposal:

1. Reduce friction in bringing up a set of packages.

Currently, there is a lot of friction in setting up a new set of interconnected packages. The packages must be in a git repository and the package author needs to run the swift package edit command for each dependency to develop them in tandem.

1. Some package authors prefer to keep their packages in a single repository.

This could be because of several reasons, for e.g.:

The packages are in very early design phase and are not ready to be published in their own repository yet. The author has a set of loosely related packages which they may or may not want to publish as a separate repository in future.

Proposed solution

We propose to add the following API in the PackageDescription module:

extension Package.Dependency {
    public static func package(path: String) -> Package.Dependency
}

• This API will only be available if the tools version of the manifest is

greater than or equal to the Swift version this proposal is implemented in.

• The value of path must be a valid absolute or relative path string.

• The package at path must be a valid Swift package.

• The local package will be used as-is and the package manager will not try to

perform any git operation on the package.

• The local package must be declared in the root package or in other local

dependencies. This means, it is not possible to depend on a regular versioned dependency that declares a local package dependency.

• A local package dependency will override any regular dependency in the package

graph that has the same package name.

• A local dependency will not be recorded in the Package.resolved file and

if it overrides a dependency in the package graph, any existing entry will be removed. This is similar to the edit mode behaviour.

• The package manager will not allow using the edit feature on local dependencies.

Impact on existing packages

None.

Alternatives considered

We considered piggybacking this on the multi-package repository feature, which would also allow authors to publish subpackages from a repository. However, we think local dependencies is a much simpler feature that stands on its own.