All concerning the Swift Package deal Supervisor and the Swift toolchain

If you do not know an excessive amount of concerning the Swift Package deal Supervisor, however you’re searching for the fundamentals please learn my tutorial about SPM that explains just about the whole lot. The purpose of this text is to go deep into the SPM structure, additionally earlier than you begin studying this I would suggest to additionally learn my article about frameworks and instruments. 📖

Prepared? Go! I imply Swift! 😂

Swift Package deal Supervisor

Have you ever ever questioned about how does SPM parse it is manifest file with the intention to set up your packages? Properly, the Package deal.swift manifest is a wierd beast. Let me present you an fast instance of a daily package deal description file:

import PackageDescription

let package deal = Package deal(
    title: "HelloSwift",
    dependencies: [
        
    ],
    targets: [
        .target(
            name: "HelloSwift",
            dependencies: []),
        .testTarget(
            title: "HelloSwiftTests",
            dependencies: ["HelloSwift"]),
    ]
)

The primary line comprises the model data, subsequent we now have to import the PackageDescription module which comprises all of the required parts to correctly describe a Swift package deal. For those who run for instance swift package deal replace all of your dependencies on this manifest file will probably be resolved & you need to use them inside your personal code information. ✅

However how on earth are they doing this magic? 💫

That query was bugging me for some time, so I did some research. First I used to be attempting to duplicate this habits with out trying on the unique implementation of the Swift Package deal Supervisor at GitHub. I knew I should not parse the Swift file, as a result of that’d be a horrible factor to do – Swift information are messy – so let’s attempt to import it by some means… 🙃

Dynamic library loading method

I looked for the “dynamic swift library” key phrases and located an attention-grabbing discussion board subject on swift.org. Yeah, I am making some progress I assumed. WRONG! I used to be method farther from the precise resolution than I although, however it was enjoyable, so I used to be trying into the implementation particulars of methods to open a compiled .dylib file utilizing dlopen & dlsym from Swift. How does one create a .dylib file? Ah, I already know this! 👍

I all the time needed to grasp this subject higher, so I began to learn increasingly more each about static and dynamic libraries. Lengthy story quick, you’ll be able to create a dynamic (or static) library with the next product definition:

import PackageDescription

let package deal = Package deal(
    title: "instance",
    merchandise: [
        .library(name: "myStaticLib", type: .static, targets: ["myStaticLib"]),
        .library(title: "myDynamicLib", sort: .dynamic, targets: ["myDynamicLib"]),
    ],
    targets: [
        .target(
            name: "myStaticLib",
            dependencies: []),
        .goal(
            title: "myDynamicLib",
            dependencies: []),
    ]
)

The necessary information are going to be positioned contained in the .construct/debug folder. The .swiftmodule is mainly the general public header file, this comprises all of the out there API in your library. The .swiftdoc file comprises the documentation for the compiled module, and relying on the kind you may additionally get a .dylib or a .a file. Guess which one is which.

So I may load the .dylib file through the use of dlopen & dlsym (some @_cdecl magic concerned to get fixed names as an alternative of the “fuzzy” ones), however I used to be continuously receiving the identical warning over and over. The dynamic loading labored effectively, however I needed to do away with the warning, so I attempted to take away the embedded the lib dependency from my executable goal. (Trace: not likely potential… afaik. anybody? 🙄)

I used to be messing round with rpaths & the install_name_tool for like hours, however even after I succesfully eliminated my library from the executable, “libSwift*issues” had been nonetheless embedded into it. So that is the unhappy state of an unstable ABI, I assumed… anyway a minimum of I’ve realized one thing essential throughout the way in which right here:

Importing Swift code into Swift!

Sure, you heard that. It is potential to import compiled Swift libraries into Swift, however not lots of people heard about this (I assume). It isn’t a preferred subject amongs iOS / UIKit builders, however SPM does this on a regular basis behind the scenes. 😅

How on earth can we import the pre-built libraries? Properly, it is fairly easy.

// utilizing swiftc with compiler flags

swiftc dynamic_main.swift -I ./.construct/debug -lmyDynamicLib -L ./.construct/debug
swiftc static_main.swift -I ./.construct/debug -lmyStaticLib -L ./.construct/debug

// utilizing the Swift Package deal Supervisor with compiler flags

swift construct -Xswiftc -I -Xswiftc ./.construct/debug -Xswiftc -L -Xswiftc ./.construct/debug -Xswiftc -lmyStaticLib
swift construct -Xswiftc -I -Xswiftc ./.construct/debug -Xswiftc -L -Xswiftc ./.construct/debug -Xswiftc -lmyDynamicLib

You simply must append just a few compiler flags. The -I stands for the import search path, -L is the library search path, -l hyperlinks the given library. Examine swiftc -h for extra particulars and flags you will not remorse it! Voilá now you’ll be able to distribute closed supply Swift packages. A minimum of it was good to understand how SPM does the “trick”. 🤓

Please word that till Swift 5 & ABI stability arrives you need to use the precompiled libraries with the identical Swift model solely! So when you compile a lib with Swift 4.2, your executable additionally must be compiled with 4.2., however it will change fairly quickly. 👏

The Swift Package deal Supervisor methodology

After 2 days of analysis & studying I actually needed to unravel this, so I’ve began to examine the supply code of SPM. The very first thing I’ve tried was including the --verbose flag after the swift construct command. Right here is the necessary factor:

/Purposes/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swiftc 
--driver-mode=swift 
-L /Purposes/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 
-lPackageDescription 
-suppress-warnings 
-swift-version 4.2 
-I /Purposes/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/lib/swift/pm/4_2 
-target x86_64-apple-macosx10.10 
-sdk /Purposes/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk 
/Customers/tib/instance/Package deal.swift 
-fileno 5

Whoa, this spits out a JSON based mostly on my Package deal.swift file!!! 🎉

How the hell are they doing this?

It seems, when you change the -fileno parameter worth to 1 (that is the usual output) you’ll be able to see the outcomes of this command on the console. Now the trick right here is that SPM merely compiles the Package deal.swift and if there’s a -fileno flag current within the command line arguments, effectively it prints out the encoded JSON illustration of the Package deal object after the method exits. That is it, fuckn’ simple, however it took 1 extra day for me to determine this out… parenting 2 children & coding is a tough mixture. 🤷‍♂️

For those who open the /Purposes/Xcode.app/Contents/Developer/ Toolchains/XcodeDefault.xctoolchain/ usr/lib/swift/pm/4_2 folder you may see 3 acquainted information there. Precisely. I additionally appeared on the supply of the Package deal.swift file from the SPM repository, and adopted the registerExitHandler methodology. After a profitable Package deal initialization it merely registers an exit handler if a -fileno argument is current encodes itself & dumps the end result through the use of the file handler quantity. Candy! 😎

Since I used to be just about within the end lap, I needed to determine yet one more factor: how did they handle to place the swift package deal command beneath the swift command?

Swift toolchain

I simply entered swift lol into my terminal. That is what occurred:

[email protected]~: swift lol
error: unable to invoke subcommand:
/Purposes/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/swift-lol
(No such file or listing)

Acquired ya! The toolchain is the important thing to the whole lot:

1. Apple is compiling the PackageDescription library from the Swift Package deal Supervisor and places the .swiftmodule, .swiftdoc, .dylib information into the right locations beneath Xcode’s default toolchain library path.
2. The swift construct, run, check subcommands are simply one other Swift binary executables positioned contained in the toolchain’s binary path. (Named like: swift-package, swift-build, swift-run, swift-test)
3. The swift command tries to invoke the right subcommand if there’s any and it is a legitimate (Swift) binary. (Tried with a shell script, it failed miserably…)
4. SPM makes use of the PackageDescription library from the toolchain with the intention to compile & flip the manifest file into JSON output.
5. The remainder is historical past. 🤐

Swift can resolve subcommands from wherever “inside” the PATH variable. You simply must prefix your Swift script with swift- and also you’re good to go.

SwiftCI – a activity runner for Swift

I had this concept that it would be good to have a grunt / gulp like activity runner additionally a steady integration service on a long run through the use of this method I defined above. So I’ve made an identical extension wired into the center of the Swift toolchain: SwiftCI. ❤️

You may seize the proof-of-concept implementation of SwiftCI from GitHub. After putting in it you’ll be able to create your personal CI.swift information and run your workflows.

import CI

let buildWorkflow = Workflow(
    title: "default",
    duties: [
        Task(name: "HelloWorld",
             url: "[email protected]:BinaryBirds/HelloWorld.git",
             model: "1.0.0",
             inputs: [:]),

        Job(title: "OutputGenerator",
             url: "~/ci/Duties/OutputGenerator",
             model: "1.0.0",
             inputs: [:]),

        Job(title: "SampleTask",
             url: "[email protected]:BinaryBirds/SampleTask.git",
             model: "1.0.1",
             inputs: ["task-input-parameter": "Hello SampleTask!"]),
    ])

let testWorkflow = Workflow(
    title: "linux",
    duties: [
        Task(name: "SampleTask",
             url: "https://github.com/BinaryBirds/SampleTask.git",
             version: "1.0.0",
             inputs: ["task-input-parameter": "Hello SampleTask!"]),
        ])

let mission = Undertaking(title: "Instance",
                      url: "[email protected]:BinaryBirds/Instance.git",
                      workflows: [buildWorkflow, testWorkflow])

The code above is a pattern from a CI.swift file, you’ll be able to merely run any workflow with the swift CI run workflow-name command. All the pieces is 100% written in Swift, even the CI workflow descriptor file. I am planning to increase my CI namespace with some useful sub-commands in a while. PR’s are greater than welcomed!

I am very pleased with the end result, not simply due to the ultimate product (that is solely a proof of idea implementation), however largely due to the issues I’ve realized throughout the creation course of.