Newbie’s information to Swift package deal supervisor command plugins

Introduction to Swift Bundle Supervisor plugins

To begin with I would 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. Actually talking I used to be a bit to lazy to fastidiously learn by way of your entire documentation, it is fairly lengthy, however lengthy story quick, you’ll be able to create the next plugin varieties with the at present present APIs:

• Construct instruments – could 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 – could be invoked by way of the command line
  • supply code formatting – modifies the code inside package deal
  • documentation technology – generate docs for the package deal
  • customized – consumer 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 had 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 straightforward, however the developer expertise it is not 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 Bundle Supervisor Command Plugins proposal.

mkdir Instance
cd Instance
swift package deal init --type=library

I began with a model new package deal, utilizing the swift package deal init command, then I modified the Bundle.swift file in line with the documentation. I’ve additionally added SwiftLint as a package deal 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 package deal = Bundle(
    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 essential.swift file proper subsequent to the Sources folder, with the next contents.

import PackagePlugin
import Basis

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

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

            strive 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 software utilizing the plugins context then it’s going to iterate by way of the obtainable package deal targets, filter out non source-module targets and format solely these targets that incorporates precise Swift supply information. The method object ought to merely invoke the underlying software, we will wait till the kid (swiftlint invocation) course of exists and hopefully we’re good to go. 🤞

Replace: kalKarmaDev informed me that it’s potential to cross the --in-process-sourcekit argument to SwiftLint, this can repair the underlying situation and the supply information are literally mounted.

I wished to record the obtainable plugins & run my supply code linter / formatter utilizing the next shell instructions, however sadly looks like the swiftlint invocation half failed for some unusual motive.

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

# error: swift-format invocation failed: NSTaskTerminationReason(rawValue: 2):5
# what the hell occurred? 🤔

Looks like 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

@essential
struct MyCommandPlugin: CommandPlugin {
    
    func performCommand(context: PluginContext, arguments: [String]) throws {
        let software = strive context.software(named: "swiftlint")
        let toolUrl = URL(fileURLWithPath: software.path.string)
        
        for goal in context.package deal.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: " "))

            strive 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 remedy this situation or not. 🤔

public struct Instance {
    public personal(set) var textual content = "Hi there, World!"

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

Seems, after I run the plugin by way of the Course of invocation, nothing occurs, however after 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 undoubtedly have an issue right here… I attempted to get the usual output message and error message from the working course of, looks like swiftlint runs, however one thing within the SPM infrastructure blocks the code adjustments within the package deal. After a number of hours of debugging I made a decision to present a shot to swift-format, as a result of that is what the official docs counsel. 🤷‍♂️

import PackageDescription

let package deal = Bundle(
    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 Bundle.swift file and the plugin supply code, to make it work with swift-format.

import PackagePlugin
import Basis

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

        
        for goal in context.package deal.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)",
            ]
            strive 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 package deal plugin command to format my supply information, however this time swift-format was doing the code formatting as a substitute of swiftlint.

swift package deal --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 allure, my Instance.swift file was mounted and the : was on the left facet… 🎊

public struct Instance {
    public personal(set) var textual content = "Hi there, World!"

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

Yeah, I’ve made some progress, nevertheless it took me numerous time to debug this situation and I do not like the truth that I’ve to fiddle with processes to invoke different instruments… my intestine tells me that SwiftLint shouldn’t be following the usual shell exit standing codes and that is inflicting some points, possibly it is spawning little one processes and that is the issue, I actually do not know however I do not wished to waste extra time on this situation, 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 personal(set) var textual content = "Hi there, 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 venture.

import PackageDescription

let package deal = Bundle(
    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 had been obtainable after I executed the plugin record command.

swift package deal plugin --list

# ‘format-source-code’ (plugin ‘MyCommandPlugin’ in package deal ‘Instance’)
# ‘generate-documentation’ (plugin ‘Swift-DocC’ in package deal ‘SwiftDocCPlugin’)
# ‘preview-documentation’ (plugin ‘Swift-DocC Preview’ in package deal ‘SwiftDocCPlugin’)

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

swift package deal generate-documentation
# Producing documentation for 'Instance'...
# Construct full! (0.16s)
# Changing documentation...
# Conversion full! (0.33s)
# Generated DocC archive at '/Customers/tib/Linter/.construct/plugins/Swift-DocC/outputs/Instance.doccarchive'

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 package deal preview-documentation 
# Observe: The Swift-DocC Preview plugin requires passing the '--disable-sandbox' flag
swift package deal --disable-sandbox preview-documentation

Magic. It labored and my documentation was obtainable. Now that is how plugins ought to work, I beloved this expertise and I actually hope that an increasing number of 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 could possibly be very helpful after I deploy feather apps, I’ve a number of module bundles there and now I’ve to manually copy all the things… 🙈

import PackageDescription

let package deal = Bundle(
    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/Sources folder I’ve positioned a easy check.json file with the next contents.

{
    "success": true
}

The primary.swift file of the MyExample goal seems to be like this. It simply validates that the useful resource file is accessible and it merely decodes the contents of it and prints all the things to the usual output. 👍

import Basis

guard let jsonFile = Bundle.module.url(forResource: "Sources/check", withExtension: "json") else {
    fatalError("Bundle file not discovered")
}
let jsonData = strive Information(contentsOf: jsonFile)

struct Json: Codable {
    let success: Bool
}

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

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

Contained in the Plugins folder I’ve created a essential.swift file underneath the MyDistCommandPlugin folder.

import PackagePlugin
import Basis

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

Now I used to be capable of re-run the swift package deal plugin –list command and the dist verb appeared within the record of obtainable 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

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

        let end result = strive 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.form == .executable }) else {
            fatalError("could not discover executable")
        }
        
        let course of = strive 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 = strive FileManager.default.contentsOfDirectory(atPath: exeUrl.path).filter { $0.hasSuffix(".bundle") }

        for bundle in bundles {
            let course of = strive 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 capable of get again the bundled sources, so I had to make use of the URL of the executable file, drop the final path element and browse the contents of that listing utilizing the FileManager to get again the .bundle packages inside that folder.

Sadly the builtArtifacts property solely returns the executables and libraries. I actually hope that we’ll get help for bundles as nicely sooner or later so this hacky resolution could be prevented for good. Anyway it really works simply effective, however nonetheless it is a hack, so use it fastidiously. ⚠️

swift package deal --allow-writing-to-package-directory dist
./MyExample 
#Is success? true

I used to be capable of run my customized dist command with out additional points, after all you should utilize further 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 a official documentation for Swift package deal 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 concerning the software invocation APIs. In abstract I can say that that is just the start. It is similar to the async / await and actors addition to the Swift language. The characteristic itself is there, it is largely able to go, however not many builders are utilizing it every day. This stuff would require time and hopefully we’ll see much more plugins afterward… 💪