iOS Development

Newbie’s information to Swift bundle supervisor command plugins

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Discover ways to create command plugins for the Swift Package deal Supervisor to execute customized actions utilizing SPM and different instruments.

Swift

Introduction to Swift Package deal Supervisor plugins


To begin with I might like to speak a couple of phrases concerning the new SPM plugin infrastructure, that was launched within the Swift 5.6 launch. The very first proposal describes the detailed design of the plugin API with some plugin examples, that are fairly helpful. Truthfully talking I used to be a bit to lazy to rigorously learn by way of your entire documentation, it is fairly lengthy, however lengthy story quick, you may create the next plugin sorts with the at the moment present APIs:


  • Construct instruments – will be invoked by way of the SPM targets
    • pre-build – runs earlier than the construct begins
    • construct – runs in the course of the construct

  • Instructions – will be invoked by way of the command line
    • supply code formatting – modifies the code inside bundle
    • documentation era – generate docs for the bundle
    • customized – person outlined intentions


For the sake of simplicity on this tutorial I am solely going to write down a bit concerning the second class, aka. the command plugins. These plugins have been a bit extra fascinating for me, as a result of I wished to combine my deployment workflow into SPM, so I began to experiment with the plugin API to see how exhausting it’s to construct such a factor. Seems it is fairly simple, however the developer expertise it isn’t that good. 😅




Constructing a supply code formatting plugin

The very very first thing I wished to combine with SPM was SwiftLint, since I used to be not capable of finding a plugin implementation that I may use I began from scratch. As a place to begin I used to be utilizing the instance code from the Package deal Supervisor Command Plugins proposal.


mkdir Instance
cd Instance
swift bundle init --type=library


I began with a model new bundle, utilizing the swift bundle init command, then I modified the Package deal.swift file in keeping with the documentation. I’ve additionally added SwiftLint as a bundle dependency so SPM can obtain & construct the and hopefully my customized plugin command can invoke the swiftlint executable when it’s wanted.



import PackageDescription

let bundle = Package deal(
    identify: "Instance",
    platforms: [
        .macOS(.v10_15),
    ],
    merchandise: [
        .library(name: "Example", targets: ["Example"]),
        .plugin(identify: "MyCommandPlugin", targets: ["MyCommandPlugin"]),
    ],
    dependencies: [
        .package(url: "https://github.com/realm/SwiftLint", branch: "master"),
    ],
    targets: [
        .target(name: "Example", dependencies: []),
        .testTarget(identify: "ExampleTests", dependencies: ["Example"]),
       
        .plugin(identify: "MyCommandPlugin",
                functionality: .command(
                    intent: .sourceCodeFormatting(),
                    permissions: [
                        .writeToPackageDirectory(reason: "This command reformats source files")
                    ]
                ),
                dependencies: [
                    .product(name: "swiftlint", package: "SwiftLint"),
                ]),
    ]
)


I’ve created a Plugins listing with a primary.swift file proper subsequent to the Sources folder, with the next contents.


import PackagePlugin
import Basis

@primary
struct MyCommandPlugin: CommandPlugin {
    
    func performCommand(context: PluginContext, arguments: [String]) throws {
        let instrument = attempt context.instrument(named: "swiftlint")
        let toolUrl = URL(fileURLWithPath: instrument.path.string)
        
        for goal in context.bundle.targets {
            guard let goal = goal as? SourceModuleTarget else { proceed }

            let course of = Course of()
            course of.executableURL = toolUrl
            course of.arguments = [
                "(target.directory)",
                "--fix",
               
            ]

            attempt course of.run()
            course of.waitUntilExit()
            
            if course of.terminationReason == .exit && course of.terminationStatus == 0 {
                print("Formatted the supply code in (goal.listing).")
            }
            else {
                let drawback = "(course of.terminationReason):(course of.terminationStatus)"
                Diagnostics.error("swift-format invocation failed: (drawback)")
            }
        }
    }
}


The snippet above ought to find the swiftlint instrument utilizing the plugins context then it will iterate by way of the out there bundle targets, filter out non source-module targets and format solely these targets that incorporates precise Swift supply recordsdata. The method object ought to merely invoke the underlying instrument, we are able to wait till the kid (swiftlint invocation) course of exists and hopefully we’re good to go. 🤞


Replace: kalKarmaDev advised me that it’s doable to cross the --in-process-sourcekit argument to SwiftLint, this may repair the underlying difficulty and the supply recordsdata are literally fastened.


I wished to record the out there plugins & run my supply code linter / formatter utilizing the next shell instructions, however sadly looks as if the swiftlint invocation half failed for some unusual cause.




swift bundle plugin --list
    swift bundle format-source-code #will not work, wants entry to supply recordsdata
    swift bundle --allow-writing-to-package-directory format-source-code



Looks as if there’s an issue with the exit code of the invoked swiftlint course of, so I eliminated the success test from the plugin supply to see if that is inflicting the difficulty or not additionally tried to print out the executable command to debug the underlying drawback.


import PackagePlugin
import Basis

@primary
struct MyCommandPlugin: CommandPlugin {
    
    func performCommand(context: PluginContext, arguments: [String]) throws {
        let instrument = attempt context.instrument(named: "swiftlint")
        let toolUrl = URL(fileURLWithPath: instrument.path.string)
        
        for goal in context.bundle.targets {
            guard let goal = goal as? SourceModuleTarget else { proceed }

            let course of = Course of()
            course of.executableURL = toolUrl
            course of.arguments = [
                "(target.directory)",
                "--fix",
            ]

            print(toolUrl.path, course of.arguments!.joined(separator: " "))

            attempt course of.run()
            course of.waitUntilExit()
        }
    }
}


Deliberately made a small “mistake” within the Instance.swift supply file, so I can see if the swiftlint –fix command will clear up this difficulty or not. 🤔


public struct Instance {
    public non-public(set) var textual content = "Hiya, World!"

    public init() {
        let xxx :Int = 123
    }
}


Seems, once I run the plugin by way of the Course of invocation, nothing occurs, however once I enter the next code manually into the shell, it simply works.


/Customers/tib/Instance/.construct/arm64-apple-macosx/debug/swiftlint /Customers/tib/Instance/Exams/Instance --fix
/Customers/tib/Instance/.construct/arm64-apple-macosx/debug/swiftlint /Customers/tib/Instance/Exams/ExampleTests --fix


All proper, so we positively have an issue right here… I attempted to get the usual output message and error message from the operating course of, looks as if swiftlint runs, however one thing within the SPM infrastructure blocks the code adjustments within the bundle. After a number of hours of debugging I made a decision to offer a shot to swift-format, as a result of that is what the official docs counsel. 🤷‍♂️



import PackageDescription

let bundle = Package deal(
    identify: "Instance",
    platforms: [
        .macOS(.v10_15),
    ],
    merchandise: [
        .library(name: "Example", targets: ["Example"]),
        .plugin(identify: "MyCommandPlugin", targets: ["MyCommandPlugin"]),
    ],
    dependencies: [
        .package(url: "https://github.com/apple/swift-format", exact: "0.50600.1"),
    ],
    targets: [
        .target(name: "Example", dependencies: []),
        .testTarget(identify: "ExampleTests", dependencies: ["Example"]),
       
        .plugin(identify: "MyCommandPlugin",
                functionality: .command(
                    intent: .sourceCodeFormatting(),
                    permissions: [
                        .writeToPackageDirectory(reason: "This command reformats source files")
                    ]
                ),
                dependencies: [
                    .product(name: "swift-format", package: "swift-format"),
                ]),
    ]
)


Modified each the Package deal.swift file and the plugin supply code, to make it work with swift-format.


import PackagePlugin
import Basis

@primary
struct MyCommandPlugin: CommandPlugin {
    
    func performCommand(context: PluginContext, arguments: [String]) throws {
        let swiftFormatTool = attempt context.instrument(named: "swift-format")
        let swiftFormatExec = URL(fileURLWithPath: swiftFormatTool.path.string)

        
        for goal in context.bundle.targets {
            guard let goal = goal as? SourceModuleTarget else { proceed }

            let course of = Course of()
            course of.executableURL = swiftFormatExec
            course of.arguments = [

                "--in-place",
                "--recursive",
                "(target.directory)",
            ]
            attempt course of.run()
            course of.waitUntilExit()

            if course of.terminationReason == .exit && course of.terminationStatus == 0 {
                print("Formatted the supply code in (goal.listing).")
            }
            else {
                let drawback = "(course of.terminationReason):(course of.terminationStatus)"
                Diagnostics.error("swift-format invocation failed: (drawback)")
            }
        }
    }
}


I attempted to run once more the very same bundle plugin command to format my supply recordsdata, however this time swift-format was doing the code formatting as a substitute of swiftlint.


swift bundle --allow-writing-to-package-directory format-source-code
// ... loading dependencies
Construct full! (6.38s)
Formatted the supply code in /Customers/tib/Linter/Exams/ExampleTests.
Formatted the supply code in /Customers/tib/Linter/Sources/Instance.


Labored like a appeal, my Instance.swift file was fastened and the : was on the left facet… 🎊


public struct Instance {
    public non-public(set) var textual content = "Hiya, World!"

    public init() {
        let xxx: Int = 123
    }
}


Yeah, I’ve made some progress, nevertheless it took me various time to debug this difficulty and I do not like the truth that I’ve to fiddle with processes to invoke different instruments… my intestine tells me that SwiftLint isn’t following the usual shell exit standing codes and that is inflicting some points, possibly it is spawning youngster processes and that is the issue, I actually do not know however I do not wished to waste extra time on this difficulty, however I wished to maneuver ahead with the opposite class. 😅





Integrating the DocC plugin with SPM


As a primary step I added some dummy feedback to my Instance library to have the ability to see one thing within the generated documentation, nothing fancy just a few one-liners. 📖



public struct Instance {

    
    public non-public(set) var textual content = "Hiya, World!"
    
    
    public init() {
        let xxx: Int = 123
    }
}


I found that Apple has an official DocC plugin, so I added it as a dependency to my mission.



import PackageDescription

let bundle = Package deal(
    identify: "Instance",
    platforms: [
        .macOS(.v10_15),
    ],
    merchandise: [
        .library(name: "Example", targets: ["Example"]),
        .plugin(identify: "MyCommandPlugin", targets: ["MyCommandPlugin"]),
    ],
    dependencies: [
        .package(url: "https://github.com/apple/swift-format", exact: "0.50600.1"),
        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),

    ],
    targets: [
        .target(name: "Example", dependencies: []),
        .testTarget(identify: "ExampleTests", dependencies: ["Example"]),
       
        .plugin(identify: "MyCommandPlugin",
                functionality: .command(
                    intent: .sourceCodeFormatting(),
                    permissions: [
                        .writeToPackageDirectory(reason: "This command reformats source files")
                    ]
                ),
                dependencies: [
                    .product(name: "swift-format", package: "swift-format"),
                ]),
    ]
)


Two new plugin instructions have been out there after I executed the plugin record command.


swift bundle plugin --list




Tried to run the primary one, and fortuitously the doccarchive file was generated. 😊


swift bundle generate-documentation





Additionally tried to preview the documentation, there was a be aware concerning the --disable-sandbox flag within the output, so I merely added it to my authentic command and…


swift bundle preview-documentation 

swift bundle --disable-sandbox preview-documentation


Magic. It labored and my documentation was out there. Now that is how plugins ought to work, I beloved this expertise and I actually hope that increasingly more official plugins are coming quickly. 😍





Constructing a customized intent command plugin


I wished to construct a small executable goal with some bundled sources and see if a plugin can deploy the executable binary with the sources. This may very well be very helpful once I deploy feather apps, I’ve a number of module bundles there and now I’ve to manually copy the whole lot… 🙈



import PackageDescription

let bundle = Package deal(
    identify: "Instance",
    platforms: [
        .macOS(.v10_15),
    ],
    merchandise: [
        .library(name: "Example", targets: ["Example"]),
        .executable(identify: "MyExample", targets: ["MyExample"]),
        .plugin(identify: "MyCommandPlugin", targets: ["MyCommandPlugin"]),
        .plugin(identify: "MyDistCommandPlugin", targets: ["MyDistCommandPlugin"]),
    ],
    dependencies: [
        .package(url: "https://github.com/apple/swift-format", exact: "0.50600.1"),
        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),

    ],
    targets: [
        .executableTarget(name: "MyExample",
                          resources: [
                            .copy("Resources"),
                          ], plugins: [
                            
                          ]),
        .goal(identify: "Instance", dependencies: []),
        .testTarget(identify: "ExampleTests", dependencies: ["Example"]),
       
        .plugin(identify: "MyCommandPlugin",
                functionality: .command(
                    intent: .sourceCodeFormatting(),
                    permissions: [
                        .writeToPackageDirectory(reason: "This command reformats source files")
                    ]
                ),
                dependencies: [
                    .product(name: "swift-format", package: "swift-format"),
                ]),
        
        .plugin(identify: "MyDistCommandPlugin",
                functionality: .command(
                    intent: .customized(verb: "dist", description: "Create dist archive"),
                    permissions: [
                        .writeToPackageDirectory(reason: "This command deploys the executable")
                    ]
                ),
                dependencies: [
                ]),
    ]
)


As a primary step I created a brand new executable goal known as MyExample and a brand new MyDistCommandPlugin with a customized verb. Contained in the Sources/MyExample/Assets folder I’ve positioned a easy take a look at.json file with the next contents.


{
    "success": true
}


The primary.swift file of the MyExample goal appears like this. It simply validates that the useful resource file is on the market and it merely decodes the contents of it and prints the whole lot to the usual output. 👍


import Basis

guard let jsonFile = Bundle.module.url(forResource: "Assets/take a look at", withExtension: "json") else {
    fatalError("Bundle file not discovered")
}
let jsonData = attempt Information(contentsOf: jsonFile)

struct Json: Codable {
    let success: Bool
}

let json = attempt JSONDecoder().decode(Json.self, from: jsonData)

print("Is success?", json.success)


Contained in the Plugins folder I’ve created a primary.swift file below the MyDistCommandPlugin folder.


import PackagePlugin
import Basis

@primary
struct MyDistCommandPlugin: CommandPlugin {
    
    func performCommand(context: PluginContext, arguments: [String]) throws {
        
        
    }
}


Now I used to be in a position to re-run the swift bundle plugin --list command and the dist verb appeared within the record of accessible instructions. Now the one query is: how will we get the artifacts out of the construct listing? Happily the third instance of the instructions proposal is kind of related.


import PackagePlugin
import Basis

@primary
struct MyDistCommandPlugin: CommandPlugin {
    
    func performCommand(context: PluginContext, arguments: [String]) throws {
        let cpTool = attempt context.instrument(named: "cp")
        let cpToolURL = URL(fileURLWithPath: cpTool.path.string)

        let end result = attempt packageManager.construct(.product("MyExample"), parameters: .init(configuration: .launch, logging: .concise))
        guard end result.succeeded else {
            fatalError("could not construct product")
        }
        guard let executable = end result.builtArtifacts.first(the place : { $0.sort == .executable }) else {
            fatalError("could not discover executable")
        }
        
        let course of = attempt Course of.run(cpToolURL, arguments: [
            executable.path.string,
            context.package.directory.string,
        ])
        course of.waitUntilExit()

        let exeUrl = URL(fileURLWithPath: executable.path.string).deletingLastPathComponent()
        let bundles = attempt FileManager.default.contentsOfDirectory(atPath: exeUrl.path).filter { $0.hasSuffix(".bundle") }

        for bundle in bundles {
            let course of = attempt Course of.run(cpToolURL, arguments: ["-R",
                                                                    exeUrl.appendingPathComponent(bundle).path,
                                                                    context.package.directory.string,
                                                                ])
            course of.waitUntilExit()
        }
    }
}


So the one drawback was that I used to be not in a position to get again the bundled sources, so I had to make use of the URL of the executable file, drop the final path part and skim the contents of that listing utilizing the FileManager to get again the .bundle packages within that folder.


Sadly the builtArtifacts property solely returns the executables and libraries. I actually hope that we will get help for bundles as properly sooner or later so this hacky answer will be averted for good. Anyway it really works simply fantastic, however nonetheless it is a hack, so use it rigorously. ⚠️


swift bundle --allow-writing-to-package-directory dist
./MyExample 


I used to be in a position to run my customized dist command with out additional points, after all you should utilize extra arguments to customise your plugin or add extra flexibility, the examples within the proposal are just about okay, nevertheless it’s fairly unlucky that there isn’t any official documentation for Swift bundle supervisor plugins simply but. 😕



Conclusion

Studying about command plugins was enjoyable, however at first it was annoying as a result of I anticipated a bit higher developer expertise relating to the instrument invocation APIs. In abstract I can say that that is only the start. It is similar to the async / await and actors addition to the Swift language. The function itself is there, it is principally able to go, however not many builders are utilizing it every day. These items would require time and hopefully we will see much more plugins in a while… 💪





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