Usage

Table of Contents


Create a Package

Simply put: a package is a git repository with semantically versioned tags, that contains Swift sources and a Package.swift manifest file at its root.

Create a library package

A library package contains code which other packages can use and depend on. To get started, create a directory and run swift package init command:

$ mkdir MyPackage
$ cd MyPackage
$ swift package init # or swift package init --type library
$ swift build
$ swift test

This will create the directory structure needed for a library package with a target and the corresponding test target to write unit tests. A library package can contain multiple targets as explained in Target Format Reference.

Create an executable package

SwiftPM can create native binary which can be executed from command line. To get started:

$ mkdir MyExecutable
$ cd MyExecutable
$ swift package init --type executable
$ swift build
$ swift run
Hello, World!

This creates the directory structure needed for executable targets. Any target can be turned into a executable target if there is a main.swift present in its sources. Complete reference for layout is here.

Define Dependencies

All you need to do to depend on a package is define the dependency and the version, in manifest of your package. For e.g. if you want to use https://github.com/apple/example-package-playingcard as a dependency, add the github URL in dependencies of your Package.swift:

import PackageDescription

let package = Package(
    name: "MyPackage",
    dependencies: [
        .Package(url: "https://github.com/apple/example-package-playingcard.git", majorVersion: 3),
    ]
)

Now you should be able to import PlayingCard anywhere in your package and use the public APIs.

Publish a package

To publish a package, you just have to initialize a git repository and create a semantic version tag:

$ git init
$ git add .
$ git remote add origin [github-URL]
$ git commit -m "Initial Commit"
$ git tag 1.0.0
$ git push origin master --tags

Now other packages can depend on version 1.0.0 of this package using the github url.
Example of a published package: https://github.com/apple/example-package-fisheryates

Require System Libraries

You can link against system libraries using the package manager. To do so, there needs to be a special package for each system library that contains a module map for that library. Such a wrapper package does not contain any code of its own.

Let's see an example of using libgit2 from an executable.

First, create a directory called example, and initialize it as a package that builds an executable:

$ mkdir example
$ cd example
example$ swift package init --type executable

Edit the Sources/main.swift so it consists of this code:

import Clibgit

let options = git_repository_init_options()
print(options)

To import Clibgit, the package manager requires that the libgit2 library has been installed by a system packager (eg. apt, brew, yum, etc.). The following files from the libgit2 system-package are of interest:

/usr/local/lib/libgit2.dylib      # .so on Linux
/usr/local/include/git2.h

Swift packages that provide module maps for system libraries are handled differently from regular Swift packages.

Note that the system library may be located elsewhere on your system, such as /usr/ rather than /usr/local/.

Create a directory called Clibgit next to the example directory and initialize it as a package that builds a system module:

example$ cd ..
$ mkdir Clibgit
$ cd Clibgit
Clibgit$ swift package init --type system-module

This creates Package.swift and module.modulemap files in the directory. Edit Package.swift and add pkgConfig parameter:

import PackageDescription

let package = Package(
    name: "Clibgit",
    pkgConfig: "libgit2"
)

The pkgConfig parameter helps SwiftPM in figuring out the include and library search paths for the system library. Note: If you don't want to use pkgConfig paramater you can pass the path to directory containing library using commandline when building your app:

example$ swift build -Xlinker -L/usr/local/lib/

Edit module.modulemap so it consists of the following:

module Clibgit [system] {
  header "/usr/local/include/git2.h"
  link "git2"
  export *
}

The convention we hope the community will adopt is to prefix such modules with C and to camelcase the modules as per Swift module name conventions. Then the community is free to name another module simply libgit which contains more “Swifty” function wrappers around the raw C interface.

Packages are Git repositories, tagged with semantic versions, containing a Package.swift file at their root. Initializing the package created a Package.swift file, but to make it a usable package we need to initialize a Git repository with at least one version tag:

Clibgit$ git init
Clibgit$ git add .
Clibgit$ git commit -m "Initial Commit"
Clibgit$ git tag 1.0.0

Now to use the Clibgit package we must declare our dependency in our example app’s Package.swift:

import PackageDescription

let package = Package(
    name: "example",
    dependencies: [
        .Package(url: "../Clibgit", majorVersion: 1)
    ]
)

Here we used a relative URL to speed up initial development. If you push your module map package to a public repository you must change the above URL reference so that it is a full, qualified git URL.

Now if we type swift build in our example app directory we will create an executable:

example$ swift build
…
example$ .build/debug/example
git_repository_init_options(version: 0, flags: 0, mode: 0, workdir_path: nil, description: nil, template_path: nil, initial_head: nil, origin_url: nil)
example$

Let’s see another example of using IJG’s JPEG library from an executable which has some caveats.

Create a directory called example, and initialize it as a package that builds an executable:

$ mkdir example
$ cd example
example$ swift package init --type executable

Edit the Sources/main.swift so it consists of this code:

import CJPEG

let jpegData = jpeg_common_struct()
print(jpegData)

Install JPEG library using a system packager e.g $ brew install jpeg

Create a directory called CJPEG next to the example directory and initialize it as a package that builds a system module:

example$ cd ..
$ mkdir CJPEG
$ cd CJPEG
CJPEG$ swift package init --type system-module

This creates Package.swift and module.modulemap files in the directory. Edit module.modulemap so it consists of the following:

module CJPEG [system] {
    header "shim.h"
    header "/usr/local/include/jpeglib.h"
    link "jpeg"
    export *
}

Create a shim.h file in the same directory and add #include <stdio.h> in it.

$ echo '#include <stdio.h>' > shim.h 

This is because jpeglib.h is not a correct module. You can also add #include <stdio.h> to the top of jpeglib.h and avoid creating shim.h file.

Create a Git repository and tag it:

CJPEG$ git init
CJPEG$ git add .
CJPEG$ git commit -m "Initial Commit"
CJPEG$ git tag 1.0.0

Now to use the CJPEG package we must declare our dependency in our example app’s Package.swift:

import PackageDescription

let package = Package(
    name: "example",
    dependencies: [
        .Package(url: "../CJPEG", majorVersion: 1)
    ]
)

Now if we type swift build in our example app directory we will create an executable:

example$ swift build -Xlinker -L/usr/local/lib/
…
example$ .build/debug/example
jpeg_common_struct(err: nil, mem: nil, progress: nil, client_data: nil, is_decompressor: 0, global_state: 0)
example$

We have to specify path where the libjpeg is present using -Xlinker because there is no pkg-config file for it. We plan to provide solution to avoid passing the flag in commandline.

Packages That Provide Multiple Libraries

Some system packages provide multiple libraries (.so and .dylib files). In such cases you should add all the libraries to that Swift modulemap package’s .modulemap file:

module CFoo [system] {
    header "/usr/local/include/foo/foo.h"
    link "foo"
    export *
}

module CFooBar [system] {
    header "/usr/include/foo/bar.h"
    link "foobar"
    export *
}

module CFooBaz [system] {
    header "/usr/include/foo/baz.h"
    link "foobaz"
    export *
}

foobar and foobaz link to foo; we don’t need to specify this information in the module-map because the headers foo/bar.h and foo/baz.h both include foo/foo.h. It is very important however that those headers do include their dependent headers, otherwise when the modules are imported into Swift the dependent modules will not get imported automatically and link errors will happen. If these link errors occur to consumers of a package that consumes your package the link errors can be especially difficult to debug.

Cross-platform Module Maps

Module maps must contain absolute paths, thus they are not cross-platform. We intend to provide a solution for this in the package manager. Long term we hope that system libraries and system packagers will provide module maps and thus this component of the package manager will become redundant.

Notably the above steps will not work if you installed JPEG and JasPer with Homebrew since the files will be installed to /usr/local for now adapt the paths, but as said, we plan to support basic relocations like these.

Module Map Versioning

Version the module maps semantically. The meaning of semantic version is less clear here, so use your best judgement. Do not follow the version of the system library the module map represents, version the module map(s) independently.

Follow the conventions of system packagers; for example, the debian package for python3 is called python3, as there is not a single package for python and python is designed to be installed side-by-side. Were you to make a module map for python3 you should name it CPython3.

System Libraries With Optional Dependencies

At this time you will need to make another module map package to represent system packages that are built with optional dependencies.

For example, libarchive optionally depends on xz, which means it can be compiled with xz support, but it is not required. To provide a package that uses libarchive with xz you must make a CArchive+CXz package that depends on CXz and provides CArchive.

Packaging legacy code

You may be working with code that builds both as a package and not. For example, you may be packaging a project that also builds with Xcode.

In these cases, you can use the build configuration SWIFT_PACKAGE to conditionally compile code for Swift packages.

#if SWIFT_PACKAGE
import Foundation
#endif

Handling version-specific logic

The package manager is designed to support packages which work with a variety of Swift project versions, including both the language and the package manager version.

In most cases, if you want to support multiple Swift versions in a package you should do so by using the language-specific version checks available in the source code itself. However, in some circumstances this may become unmanageable; in particular, when the package manifest itself cannot be written to be Swift version agnostic (for example, because it optionally adopts new package manager features not present in older versions).

The package manager has support for a mechanism to allow Swift version-specific customizations for the both package manifest and the package versions which will be considered.

Version-specific tag selection

The tags which define the versions of the package available for clients to use can optionally be suffixed with a marker in the form of @swift-3. When the package manager is determining the available tags for a repository, if a version-specific marker is available which matches the current tool version, then it will only consider the versions which have the version-specific marker. Conversely, version-specific tags will be ignored by any non-matching tool version.

For example, suppose the package Foo has the tags [1.0.0, 1.2.0@swift-3, 1.3.0]. If version 3.0 of the package manager is evaluating the available versions for this repository, it will only ever consider version 1.2.0. However, version 4.0 would consider only 1.0.0 and 1.3.0.

This feature is intended for use in the following scenarios:

  1. A package wishes to maintain support for Swift 3.0 in older versions, but newer versions of the package require Swift 4.0 for the manifest to be readable. Since Swift 3.0 will not know to ignore those versions, it would fail when performing dependency resolution on the package if no action is taken. In this case, the author can re-tag the last versions which supported Swift 3.0 appropriately.

  2. A package wishes to maintain dual support for Swift 3.0 and Swift 4.0 at the same version numbers, but this requires substantial differences in the code. In this case, the author can maintain parallel tag sets for both versions.

It is not expected the packages would ever use this feature unless absolutely necessary to support existing clients. In particular, packages should not adopt this syntax for tagging versions supporting the latest GM Swift version.

The package manager supports looking for any of the following marked tags, in order of preference:

  1. MAJOR.MINOR.PATCH (e.g., 1.2.0@swift-3.1.2)
  2. MAJOR.MINOR (e.g., 1.2.0@swift-3.1)
  3. MAJOR (e.g., 1.2.0@swift-3)

Version-specific manifest selection

The package manager will additionally look for a version-specific marked manifest version when loading the particular version of a package, by searching for a manifest in the form of Package@swift-3.swift. The set of markers looked for is the same as for version-specific tag selection.

This feature is intended for use in cases where a package wishes to maintain compatibility with multiple Swift project versions, but requires a substantively different manifest file for this to be viable (e.g., due to changes in the manifest API).

It is not expected the packages would ever use this feature unless absolutely necessary to support existing clients. In particular, packages should not adopt this syntax for tagging versions supporting the latest GM Swift version.

Editable Packages

Swift package manager supports editing dependencies, when your work requires making a change to one of your dependencies (for example, to fix a bug, or add a new API). The package manager moves the dependency into a location under Packages/ directory where it can be edited.

For the packages which are in the editable state, swift build will always use the exact sources in this directory to build, regardless of its state, git repository status, tags, or the tag desired by dependency resolution. In other words, this will just build against the sources that are present. When an editable package is present, it will be used to satisfy all instances of that package in the depencency graph. It is possible to edit all, some, or none of the packages in a dependency graph, without restriction.

Editable packages are best used to do experimentation with dependency code or create and submit a patch in the dependency owner's repository (upstream). There are two ways to put a package in editable state:

$ swift package edit Foo --branch bugFix

This will create a branch called bugFix from currently resolved version and put the dependency Foo in Packages/ directory.

$ swift package edit Foo --revision 969c6a9

This is similar to previous version except that the Package Manager will leave the dependency at a detched HEAD on the specified revision.

Note: It is necessary to provide either a branch or revision option. The rationale here is that checking out the currently resolved version would leave the repository on a detached HEAD, which is confusing. Explict options makes the action predictable for user.

Once a package is in an editable state, you can navigate to the directory Packages/Foo to make changes, build and then push the changes or open a pull request to the upstream repository.

You can end editing a package using unedit command:

$ swift package unedit Foo

This will remove the edited dependency from Packages/ and put the originally resolved version back.

This command fails if there are uncommited changes or changes which are not pushed to the remote repository. If you want to discard these changes and unedit, you can use the --force option:

$ swift package unedit Foo --force

Top of Tree Development

This feature allows overriding a dependency with a local checkout on the filesystem. This checkout is completely unmanaged by the package manager and will be used as-is. The only requirement is — the package name in the overridden checkout should not change. This is extremely useful when developing multiple packages in tandem or when working on packages alongside an application.

The command to attach (or create) a local checkout is:

$ swift package edit <package name> --path <path/to/dependency>

For e.g., if Foo depends on Bar and you have a checkout of Bar at /workspace/bar:

foo$ swift package edit Bar --path /workspace/bar

A checkout of Bar will be created if it doesn't exist at the given path. If checkout a exists, package manager will validate the package name at the given path and attach to it.

The package manager will also create a symlink in Packages/ directory to the checkout path.

Use unedit command to stop using the local checkout:

$ swift package unedit <package name>
# Example:
$ swift package unedit Bar

Package Pinning

Swift package manager has package pinning feature, also called dependency locking in some dependency managers. Pinning refers to the practice of controlling exactly which specific version of a dependency is selected by the dependency resolution algorithm, independent from the semantic versioning specification. Thus, it is a way of instructing the package manager to select a particular version from among all of the versions of a package which could be chosen while honoring the dependency constraints.

The package manager uses a file named Package.pins(“pins file”) to record the pinning information. The exact file format is unspecified/implementation defined, however, in practice it is a JSON data file. This file may be checked into SCM by the user, so that its effects apply to all users of the package. However, it may also be maintained only locally (e.g., placed in the .gitignore file). We intend to leave it to package authors to decide which use case is best for their project. We will recommend that it not be checked in by library authors, at least for released versions, since pins are not inherited and thus this information may be confusing.

In the presence of a top-level Package.pins file, the package manager will respect the pinned dependencies recorded in the file whenever it needs to do dependency resolution (e.g., on the initial checkout or when updating). In the absence of a top-level Package.pins file, the package manager will operate based purely on the requirements specified in the package manifest, but will then automatically record the choices it makes into a Package.pins file as part of the automatic pinning feature.

Automatic Pinning

The package manager has automatic pinning enabled by default (this is equivalent to swift package pin --enable-autopin). The package manager will automatically record all package dependencies in the pins file. Package project owners can choose to disable this if they wish to have more fine grained control over their pinning behavior, for e.g. pin only certain dependencies.

The automatic pinning behavior works as follows:

  • When enabled, the package manager will write all dependency versions into the pin file after any operation which changes the set of active working dependencies (for example, if a new dependency is added).

  • A package author can still change the individual pinned versions using the package pin commands (explained below), these will simply update the pinned state.

  • Some commands do not make sense when automatic pinning is enabled; for example, it is not possible to unpin and attempts to do so will produce an error.

Since package pin information is not inherited across dependencies, our recommendation is that packages which are primarily intended to be consumed by other developers either disable automatic pinning or put the Package.pins file into .gitignore, so that users are not confused why they get different versions of dependencies that are those being used by the library authors while they develop.

Pinning Commands (Manual Pinning)

  1. Pinning:

     $ swift package pin ( --all | <package-name> [--version <version>] ) [--message <message>]
    

    The package-name refers to the name of the package as specified in its manifest.

    This command pins one or all dependencies. The command which pins a single version can optionally take a specific version to pin to, if unspecified (or with --all) the behavior is to pin to the current package version in use. Examples:

    • $ swift package pin --all - pins all the dependencies.
    • $ swift package pin Foo - pins Foo at current resolved version.
    • $ swift package pin Foo --version 1.2.3 - pins Foo at 1.2.3. The specified version should be valid and resolvable.

    The --message option is an optional argument to document the reason for pinning a dependency. This could be helpful for user to later remember why a dependency was pinned. Example:

     $ swift package pin Foo --message "The patch updates for Foo are really unstable and need screening."
    
  2. Toggle automatic pinning:

     $ swift package pin ( [--enable-autopin] | [--disable-autopin] )
    

    These will enable or disable automatic pinning for the package (this state is recorded in the Package.pins file).

  3. Unpinning:

     $ swift package unpin [<package-name>]
    

    This is the counterpart to the pin command, and unpins packages.

    Note: It is an error to attempt to unpin when automatic pinning is enabled.

  4. Package update with pinning:

     $ swift package update [--repin]
    

    The default behavior is to update all unpinned packages to the latest possible versions which can be resolved while respecting the existing pins.

    The --repin argument can be used to lift the version pinning restrictions. In this case, the behavior is that all packages are updated, and packages which were previously pinned are then repinned to the latest resolved versions.

    When automatic pinning is enabled, package update act as if --repin was specified.

Swift Tools Version

The tools version declares the minimum version of the Swift tools required to use the package, determines what version of the PackageDescription API should be used in the Package.swift manifest, and determines which Swift language compatibility version should be used to parse the Package.swift manifest.

When resolving package dependencies, if the version of a dependency that would normally be chosen specifies a Swift tools version which is greater than the version in use, that version of the dependency will be considered ineligible and dependency resolution will continue with evaluating the next-best version. If no version of a dependency (which otherwise meets the version requirements from the package dependency graph) supports the version of the Swift tools in use, a dependency resolution error will result.

Swift Tools Version Specification

The Swift tools version is specified by a special comment in the first line of the Package.swift manifest. To specify a tools version, a Package.swift file must begin with the string // swift-tools-version:, followed by a version number specifier.

The version number specifier follows the syntax defined by semantic versioning 2.0, with an amendment that the patch version component is optional and considered to be 0 if not specified. The semver syntax allows for an optional pre-release version component or build version component; those components will be completely ignored by the package manager currently.
After the version number specifier, an optional ; character may be present; it, and anything else after it until the end of the first line, will be ignored by this version of the package manager, but is reserved for the use of future versions of the package manager.

Some Examples:

// swift-tools-version:3.1
// swift-tools-version:3.0.2
// swift-tools-version:4.0

Tools Version Commands

The following Swift tools version commands are supported:

  • Report tools version of the package:

      $ swift package tools-version
    
  • Set the package's tools version to the version of the tools currently in use:

      $ swift package tools-version --set-current 
    
  • Set the tools version to a given value:

      $ swift package tools-version --set <value> 
    

Prefetching Dependencies

You can pass --enable-prefetching option to swift build, swift package and swift test to enable prefetching of dependencies. That means the missing dependencies will be cloned in parallel. For e.g.:

$ swift build --enable-prefetching

Testing

Use swift test tool to run tests of a Swift package. For more information on the test tool, run swift test --help.

Running

Use swift run [executable [arguments...]] tool to run an executable product of a Swift package. The executable's name is optional when running without arguments and when there is only one executable product. For more information on the run tool, run swift run --help.

Build Configurations

SwiftPM allows two build configurations: Debug (default) and Release.

Debug

By default, running swift build will build in debug configuration. Alternatively, you can also use swift build -c debug. The build artifacts are located in directory called debug under build folder. A Swift target is built with following flags in debug mode:

  • -Onone: Compile without any optimization.
  • -g: Generate debug information.
  • -enable-testing: Enable Swift compiler's testability feature.

A C language target is build with following flags in debug mode:

  • -O0: Compile without any optimization.
  • -g: Generate debug information.

Release

To build in release mode, type: swift build -c release. The build artifacts are located in directory called release under build folder. A Swift target is built with following flags in release mode:

  • -O: Compile with optimizations.
  • -whole-module-optimization: Optimize input files (per module) together instead of individually.

A C language target is build with following flags in release mode:

  • -O2: Compile with optimizations.

Depending on Apple Modules

At this time there is no explicit support for depending on UIKit, AppKit, etc, though importing these modules should work if they are present in the proper system location. We will add explicit support for system dependencies in the future. Note that at this time the Package Manager has no support for iOS, watchOS, or tvOS platforms.

C language targets

The C language targets are similar to Swift targets except that the C language libraries should contain a directory named include to hold the public headers.

To allow a Swift target to import a C language target, add a target dependency in the manifest file. Swift Package Manager will automatically generate a modulemap for each C language library target for these 3 cases:

  • If include/Foo/Foo.h exists and Foo is the only directory under the include directory then include/Foo/Foo.h becomes the umbrella header.

  • If include/Foo.h exists and include contains no other subdirectory then include/Foo.h becomes the umbrella header.

  • Otherwise if the include directory only contains header files and no other subdirectory, it becomes the umbrella directory.

In case of complicated include layouts, a custom module.modulemap can be provided inside include. SwiftPM will error out if it can not generate a modulemap w.r.t the above rules.

For executable targets, only one valid C language main file is allowed i.e. it is invalid to have main.c and main.cpp in the same target.

Shell completion scripts

SwiftPM ships with completion scripts for both Bash and ZSH. These files should be generated in order to use them.

Bash

Use the following commands to install the Bash completions to ~/.swift-package-complete.bash and automatically load them using your ~/.bash_profile file.

swift package completion-tool generate-bash-script > ~/.swift-package-complete.bash
echo -e "source ~/.swift-package-complete.bash\n" >> ~/.bash_profile
source ~/.swift-package-complete.bash

ZSH

Use the following commands to install the ZSH completions to ~/.zsh/_swift. You can chose a different folder, but the filename should be _swift. This will also add ~/.zsh to your $fpath using your ~/.zshrc file.

mkdir ~/.zsh
swift package completion-tool generate-zsh-script > ~/.zsh/_swift
echo -e "fpath=(~/.zsh \$fpath)\n" >> ~/.zshrc
compinit