[swift-evolution] [Draft] SwiftPM: Adding development package as a dependency

Ankit Agarwal ankit at ankit.im
Tue Mar 29 13:33:30 CDT 2016

SwiftPM: Adding development package as a dependency

   - Proposal: SE-NNNN
   - Author(s): Ankit Aggarwal <https://github.com/aciidb0mb3r>
   - Status: *Awaiting review*
   - Review manager: TBD


I propose to enable SwiftPM to use a package that is still under
development as a dependency for another package during testing and

During development of libraries, developers commonly want to try out their
module package as a dependency. This emulates the typical library use-case
and is currently not possible in SwiftPM without first checking in and
tagging that library. These extra steps, while reasonable for an
already-built package, are an unnecessary burden for a package that remains
in development.

Forcing the user to modify the library package inside Packages to continue
development or continuously reclone the package after recommiting and
retagging strain the process of building the library in the first place.
Detail Design

Under this proposal, the *root* package will be allowed to specify a
DevPackage dependency. This dependency will *not *clone the package inside
Packages/ or require the dependency to be under version control. This will
free the developer to continue iterative testing, expansion, and
enhancements without being tied to the current dependency system.

This approach limits DevPackage dependencies to local file systems. Remote
repositories cannot be used with this keyword.

The following example demonstrates what a manifest file would look like. In
this example, the DevPackage is specified using a local path and the
majorVersion is used as is for this DevPackage.

import PackageDescription
let package = Package(
    name: "MyLibraryTester",
    dependencies: [
majorVersion: 1),
        .DevPackage(localPath: "../MyAwesomeLibrary", majorVersion: 1),

Under this design:

   - DevPackage is limited strictly to the root package. The manifest of
   any dependency containing a DevPackage will fail to build.
   - A DevPackage is not copied inside Packages/ and does not require
   version control.
   - SwiftPM uses the DevPackage's source directory for building,
   permitting in-place development on the local file system.
   - SwiftPM disallows non-local DevPackage sources. To use a remote
   package, the developer must first clone a package and then specify the
   local path.
   - Version numbers are specified for DevPackage entries within the
   manifest file.
   - Should the DevPackage version not be selected after resolving the
   dependency graph, the build will succeed with a warning.

Impact on existing code

This proposal does not impact existing code.
Alternatives considered

I propose two possible alternatives to this problem:

   1. Create a executable target within the library package for development
   2. Use XCTest to test the library.

Both alternate approaches permit testing a library module but they will not
simulate a full SwiftPM package.

Thanks to Erica Sadun <https://github.com/erica> for inputs.


Github link:

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