Initial support for declaring package extension targets and defining their capability.

This is guarded by a feature flag until the proposal is accepted and any requested changes have been implemented.  Until then, extensions can be enabled by setting SWIFTPM_ENABLE_EXTENSION_TARGETS=1 in the environment.

Package extension targets don't yet do anything in this commit — that will come in future commits.  But they can be declared in manifests, and they are present in the project model.  They show up in generated manifest sources and in package descriptions.  This commit includes a test fixture that will also be expanded on and used in future unit tests.

Author: abertelrud

Fixtures/Miscellaneous/Extensions/MySourceGenExtension/Package.swift

@@ -0,0 +1,53 @@
+// swift-tools-version: 999.0
+import PackageDescription
+
+let package = Package(
+    name: "MySourceGenExtension",
+    products: [
+        // The product that vends MySourceGenExt to client packages.
+        // .extension(
+        //     name: "MySourceGenExt",
+        //     target: "MySourceGenExt"
+        // )
+    ],
+    targets: [
+        // The target that implements the extension and generates commands to invoke MySourceGenTool.
+        .extension(
+            name: "MySourceGenExt",
+            capability: .prebuild(),
+            dependencies: [
+                "MySourceGenTool"
+            ]
+        ),
+        // The command line tool that generates source files.
+        .executableTarget(
+            name: "MySourceGenTool",
+            dependencies: [
+                "MySourceGenToolLib"
+            ]
+        ),
+        // A library used by MySourceGenTool (not the client).
+        .executableTarget(
+            name: "MySourceGenToolLib"
+        ),
+        // A runtime library that the client needs to link against.
+        .target(
+            name: "MySourceGenRuntimeLib"
+        ),
+        // A local tool that uses the extension.
+        .executableTarget(
+            name: "MyLocalTool",
+            dependencies: [
+                "MySourceGenExt"
+            ]
+        ),
+        // Unit tests for the extension.
+        .testTarget(
+            name: "MySourceGenExtTests",
+            dependencies: [
+                "MySourceGenExt",
+                "MySourceGenRuntimeLib"
+            ]
+        )
+    ]
+)

Fixtures/Miscellaneous/Extensions/MySourceGenExtension/Sources/MyLocalTool/main.swift

@@ -0,0 +1 @@
+print("Exec: \\(name)")

Fixtures/Miscellaneous/Extensions/MySourceGenExtension/Sources/MySourceGenExt/extension.swift

@@ -0,0 +1,4 @@
+import PackageExtension
+
+print("Hello MySourceGenExt")
+print(targetBuildContext)

Fixtures/Miscellaneous/Extensions/MySourceGenExtension/Sources/MySourceGenRuntimeLib/library.swift

@@ -0,0 +1,3 @@
+public func GetLibraryName() -> String {
+    return "MySourceGenRuntimeLib"
+}

Fixtures/Miscellaneous/Extensions/MySourceGenExtension/Sources/MySourceGenTool/main.swift

@@ -0,0 +1 @@
+print("Hello MySourceGenTool")

Fixtures/Miscellaneous/Extensions/MySourceGenExtension/Sources/MySourceGenToolLib/library.swift

@@ -0,0 +1,3 @@
+public func GetLibraryName() -> String {
+    return "MySourceGenToolLib"
+}

Fixtures/Miscellaneous/Extensions/MySourceGenExtension/Tests/MySourceGenExtTests/MySourceGenExtTests.swift

@@ -0,0 +1,47 @@
+import XCTest
+import class Foundation.Bundle
+
+final class SwiftyProtobufTests: XCTestCase {
+    func testExample() throws {
+        // This is an example of a functional test case.
+        // Use XCTAssert and related functions to verify your tests produce the correct
+        // results.
+
+        // Some of the APIs that we use below are available in macOS 10.13 and above.
+        guard #available(macOS 10.13, *) else {
+            return
+        }
+
+        // Mac Catalyst won't have `Process`, but it is supported for executables.
+        #if !targetEnvironment(macCatalyst)
+
+        let fooBinary = productsDirectory.appendingPathComponent("MySourceGenTool")
+
+        let process = Process()
+        process.executableURL = fooBinary
+
+        let pipe = Pipe()
+        process.standardOutput = pipe
+
+        try process.run()
+        process.waitUntilExit()
+
+        let data = pipe.fileHandleForReading.readDataToEndOfFile()
+        let output = String(data: data, encoding: .utf8)
+
+        XCTAssertEqual(output, "Hello, world!\n")
+        #endif
+    }
+
+    /// Returns path to the built products directory.
+    var productsDirectory: URL {
+      #if os(macOS)
+        for bundle in Bundle.allBundles where bundle.bundlePath.hasSuffix(".xctest") {
+            return bundle.bundleURL.deletingLastPathComponent()
+        }
+        fatalError("couldn't find the products directory")
+      #else
+        return Bundle.main.bundleURL
+      #endif
+    }
+}

Sources/Build/BuildPlan.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright 2015 - 2019 Apple Inc. and the Swift project authors
+ Copyright 2015 - 2021 Apple Inc. and the Swift project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See http://swift.org/LICENSE.txt for license information
@@ -702,7 +702,7 @@ public final class SwiftTargetBuildDescription {
         case .library, .test:
             result.append("-parse-as-library")
 
-        case .executable, .systemModule, .binary:
+        case .executable, .systemModule, .binary, .extension:
             do { }
         }
 
@@ -1360,7 +1360,7 @@ public class BuildPlan {
                     buildParameters: buildParameters,
                     fileSystem: fileSystem,
                     diagnostics: diagnostics))
-            case is SystemLibraryTarget, is BinaryTarget:
+            case is SystemLibraryTarget, is BinaryTarget, is ExtensionTarget:
                  break
             default:
                  fatalError("unhandled \(target.underlyingTarget)")
@@ -1595,6 +1595,8 @@ public class BuildPlan {
                     if let library = xcFrameworkLibrary(for: binaryTarget) {
                         libraryBinaryPaths.insert(library.binaryPath)
                     }
+                case .extension:
+                    continue
                 }
 
             case .product(let product, _):

Sources/Commands/Describe.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+ Copyright (c) 2014 - 2021 Apple Inc. and the Swift project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See http://swift.org/LICENSE.txt for license information
@@ -132,12 +132,29 @@ fileprivate struct DescribedPackage: Encodable {
         }
     }
 
+    /// Represents a extension capability for the sole purpose of generating a description.
+    struct DescribedExtensionCapability: Encodable {
+        let type: String
+
+        init(from capability: ExtensionCapability, in package: Package) {
+            switch capability {
+            case .prebuild:
+                self.type = "prebuild"
+            case .buildTool:
+                self.type = "buildTool"
+            case .postbuild:
+                self.type = "postbuild"
+            }
+        }
+    }
+
     /// Represents a target for the sole purpose of generating a description.
     struct DescribedTarget: Encodable {
         let name: String
         let type: String
         let c99name: String?
         let moduleType: String?
+        let extensionCapability: DescribedExtensionCapability?
         let path: String
         let sources: [String]
         let resources: [PackageModel.Resource]?
@@ -149,6 +166,7 @@ fileprivate struct DescribedPackage: Encodable {
             self.type = target.type.rawValue
             self.c99name = target.c99name
             self.moduleType = String(describing: Swift.type(of: target))
+            self.extensionCapability = (target as? ExtensionTarget).map{ DescribedExtensionCapability(from: $0.capability, in: package) }
             self.path = target.sources.root.relative(to: package.path).pathString
             self.sources = target.sources.relativePaths.map{ $0.pathString }
             self.resources = target.resources.isEmpty ? nil : target.resources

Sources/PackageDescription/PackageDescription.swift

@@ -1,7 +1,7 @@
 /*
  This source file is part of the Swift.org open source project
 
- Copyright (c) 2018 Apple Inc. and the Swift project authors
+ Copyright (c) 2018 - 2021 Apple Inc. and the Swift project authors
  Licensed under Apache License v2.0 with Runtime Library Exception
 
  See http://swift.org/LICENSE.txt for license information
@@ -592,6 +592,30 @@ extension SystemPackageProvider: Encodable {
     }
 }
 
+extension Target.ExtensionCapability: Encodable {
+    private enum CodingKeys: CodingKey {
+        case type
+    }
+
+    private enum Capability: String, Encodable {
+        case prebuild
+        case buildTool
+        case postbuild
+    }
+
+    public func encode(to encoder: Encoder) throws {
+        var container = encoder.container(keyedBy: CodingKeys.self)
+        switch self {
+        case ._prebuild:
+            try container.encode(Capability.prebuild, forKey: .type)
+        case ._buildTool:
+            try container.encode(Capability.buildTool, forKey: .type)
+        case ._postbuild:
+            try container.encode(Capability.postbuild, forKey: .type)
+        }
+    }
+}
+
 extension Target.Dependency: Encodable {
     private enum CodingKeys: CodingKey {
         case type
@@ -650,6 +674,7 @@ func manifestToJSON(_ package: Package) -> String {
     }
 
     let encoder = JSONEncoder()
+    encoder.outputFormatting = [.prettyPrinted, .sortedKeys, .withoutEscapingSlashes]
     let data = try! encoder.encode(Output(package: package, errors: errors))
     return String(data: data, encoding: .utf8)!
 }