All concerning the Swift Bundle Supervisor and the Swift toolchain

If you do not know an excessive amount of concerning the Swift Bundle Supervisor, however you might be on the lookout for the fundamentals please learn my tutorial about SPM that explains just about every little thing. The intention of this text is to go deep into the SPM structure, additionally earlier than you begin studying this I might suggest to additionally learn my article about frameworks and instruments. 📖

Prepared? Go! I imply Swift! 😂

Swift Bundle Supervisor

Have you ever ever puzzled about how does SPM parse it is manifest file to be able to set up your packages? Properly, the Bundle.swift manifest is an odd beast. Let me present you an fast instance of a daily package deal description file:

import PackageDescription

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

The primary line accommodates the model info, subsequent now we have to import the PackageDescription module which accommodates all of the required components to correctly describe a Swift package deal. If you happen to run for instance swift package deal replace all of your dependencies on this manifest file can be resolved & you need to use them inside your individual code recordsdata. ✅

However how on earth are they doing this magic? 💫

That query was bugging me for some time, so I did a little analysis. First I used to be making an attempt to copy this habits with out wanting on the unique implementation of the Swift Bundle 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 recordsdata are messy – so let’s attempt to import it someway… 🙃

Dynamic library loading method

I looked for the “dynamic swift library” key phrases and located an attention-grabbing discussion board matter on swift.org. Yeah, I am making some progress I believed. WRONG! I used to be approach farther from the precise answer than I although, however it was enjoyable, so I used to be wanting into the implementation particulars of the best way 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 matter 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 = Bundle(
    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 essential recordsdata are going to be situated contained in the .construct/debug folder. The .swiftmodule is mainly the general public header file, this accommodates all of the out there API in your library. The .swiftdoc file accommodates the documentation for the compiled module, and relying on the sort you may additionally get a .dylib or a .a file. Guess which one is which.

So I might load the .dylib file by utilizing dlopen & dlsym (some @_cdecl magic concerned to get fixed names as a substitute of the “fuzzy” ones), however I used to be continually receiving the identical warning over and over. The dynamic loading labored properly, however I needed to eliminate 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 believed… 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 matter 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 Bundle 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 need to append a number of compiler flags. The -I stands for the import search path, -L is the library search path, -l hyperlinks the given library. Verify swiftc -h for extra particulars and flags you will not remorse it! Voilá now you’ll be able to distribute closed supply Swift packages. At the least it was good to know the way 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 in the event you compile a lib with Swift 4.2, your executable additionally must be compiled with 4.2., however this can change fairly quickly. 👏

The Swift Bundle Supervisor technique

After 2 days of analysis & studying I actually needed to resolve 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 essential 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/Bundle.swift 
-fileno 5

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

How the hell are they doing this?

It seems, in the event 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 Bundle.swift and if there’s a -fileno flag current within the command line arguments, properly it prints out the encoded JSON illustration of the Bundle object after the method exits. That is it, fuckn’ straightforward, however it took 1 extra day for me to determine this out… parenting 2 children & coding is a tough mixture. 🤷‍♂️

If you happen to open the /Purposes/Xcode.app/Contents/Developer/ Toolchains/XcodeDefault.xctoolchain/ usr/lib/swift/pm/4_2 folder you may see 3 acquainted recordsdata there. Precisely. I additionally appeared on the supply of the Bundle.swift file from the SPM repository, and adopted the registerExitHandler technique. After a profitable Bundle initialization it merely registers an exit handler if a -fileno argument is current encodes itself & dumps the outcome by utilizing the file handler quantity. Candy! 😎

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

Swift toolchain

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

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

Bought ya! The toolchain is the important thing to every little thing:

1. Apple is compiling the PackageDescription library from the Swift Bundle Supervisor and places the .swiftmodule, .swiftdoc, .dylib recordsdata into the correct locations below Xcode’s default toolchain library path.
2. The swift construct, run, take a look at 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 correct subcommand if there may be 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 to be able 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 need to prefix your Swift script with swift- and also you’re good to go.

SwiftCI – a job runner for Swift

I had this concept that it might be good to have a grunt / gulp like job runner additionally a steady integration service on a long run by utilizing this system I defined above. So I’ve made an analogous extension wired into the guts of the Swift toolchain: SwiftCI. ❤️

You’ll be able to seize the proof-of-concept implementation of SwiftCI from GitHub. After putting in it you’ll be able to create your individual CI.swift recordsdata 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 challenge = 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. The whole lot is 100% written in Swift, even the CI workflow descriptor file. I am planning to increase my CI namespace with some useful sub-commands afterward. PR’s are greater than welcomed!

I am very proud of the outcome, not simply due to the closing product (that is solely a proof of idea implementation), however largely due to the issues I’ve realized in the course of the creation course of.