Plugin to display lint errors on project build

Package.swift

@@ -1,4 +1,4 @@
-// swift-tools-version:5.7
+// swift-tools-version:5.9
 import PackageDescription
 
 let package = Package(
@@ -7,8 +7,15 @@ let package = Package(
         .executable(name: "swiftformat", targets: ["CommandLineTool"]),
         .library(name: "SwiftFormat", targets: ["SwiftFormat"]),
         .plugin(name: "SwiftFormatPlugin", targets: ["SwiftFormatPlugin"]),
+        .plugin(name: "SwiftFormatLinterBuildToolPlugin", targets: ["SwiftFormatLinterBuildToolPlugin"]),
     ],
     targets: [
+        .plugin(
+            name: "SwiftFormatLinterBuildToolPlugin",
+            capability: .buildTool(),
+            dependencies: [.target(name: "CommandLineTool")],
+            path: "Plugins/SwiftFormatLinterBuildToolPlugin"
+        ),
         .executableTarget(
             name: "CommandLineTool", dependencies: ["SwiftFormat"], path: "CommandLineTool",
             exclude: ["swiftformat"]

Plugins/SwiftFormatLinterBuildToolPlugin/Path+Extension.swift

@@ -0,0 +1,60 @@
+//
+//  Path+Extension.swift
+//  SwiftFormat
+//
+//  Created by Baptiste Clarey Sjöstrand
+//  Copyright 2025 Nick Lockwood
+//
+//  Distributed under the permissive MIT license
+//  Get the latest version from here:
+//
+//  https://github.com/nicklockwood/SwiftFormat
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import Foundation
+import PackagePlugin
+
+extension Path {
+    /// Traverses up from the current path to find a directory containing a `.swiftformat` file.
+    func resolveWorkingDirectory(in directory: Path) throws -> Path {
+        guard "\(self)".hasPrefix("\(directory)") else {
+            throw PluginError.pathNotInDirectory(path: self, directory: directory)
+        }
+
+        let path: Path? = sequence(first: self) { path in
+            let path: Path = path.removingLastComponent()
+            guard "\(path)".hasPrefix("\(directory)") else {
+                return nil
+            }
+            return path
+        }
+        .reversed()
+        .first(where: { path in
+            FileManager.default.fileExists(atPath: "\(path)/\(Plugin.configFileName)")
+        })
+
+        return path ?? directory
+    }
+
+    var depth: Int {
+        URL(fileURLWithPath: "\(self)").pathComponents.count
+    }
+}

Plugins/SwiftFormatLinterBuildToolPlugin/Plugin.swift

@@ -0,0 +1,138 @@
+//
+//  Plugin.swift
+//  SwiftFormat
+//
+//  Created by Baptiste Clarey Sjöstrand
+//  Copyright 2025 Nick Lockwood
+//
+//  Distributed under the permissive MIT license
+//  Get the latest version from here:
+//
+//  https://github.com/nicklockwood/SwiftFormat
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import Foundation
+import PackagePlugin
+
+@main
+struct Plugin: BuildToolPlugin {
+    static let configFileName = ".swiftformat"
+
+    /// Creates build commands to run SwiftFormat on the target's swift files.
+    func createBuildCommands(
+        context: PluginContext,
+        target: Target,
+    ) async throws -> [Command] {
+        try makeCommand(
+            executable: context.tool(named: "swiftformat"),
+            swiftFiles: (target as? SourceModuleTarget).flatMap(swiftFiles) ?? [],
+            buildEnvironment: createBuildEnvironment(context: context, target: target),
+            pluginWorkDirectory: context.pluginWorkDirectory,
+        )
+    }
+
+    private func createBuildEnvironment(
+        context: PluginContext,
+        target: Target,
+    ) throws -> [String: String] {
+        let workingDirectory: Path = try target.directory.resolveWorkingDirectory(in: context.package.directory)
+        // The BUILD_WORKSPACE_DIRECTORY environment variable is used by SwiftFormat to find the configuration file.
+        return ["BUILD_WORKSPACE_DIRECTORY": "\(workingDirectory)"]
+    }
+
+    private func makeCommand(
+        executable: PluginContext.Tool,
+        swiftFiles: [Path],
+        buildEnvironment: [String: String],
+        pluginWorkDirectory path: Path,
+    ) throws -> [Command] {
+        guard !swiftFiles.isEmpty else {
+            return []
+        }
+        print("Environment:", buildEnvironment)
+        let arguments: [String] = [
+            "--lint", // Report errors for unformatted files.
+        ]
+        let outputPath: Path = path.appending("Output")
+        try FileManager.default.createDirectory(atPath: outputPath.string, withIntermediateDirectories: true)
+        return [
+            .prebuildCommand(
+                displayName: "SwiftFormat",
+                executable: executable.path,
+                arguments: arguments + swiftFiles.map(\.string),
+                environment: buildEnvironment,
+                outputFilesDirectory: outputPath,
+            ),
+        ]
+    }
+
+    private func swiftFiles(from target: SourceModuleTarget) -> [Path] {
+        target.sourceFiles(withSuffix: "swift").map(\.path)
+    }
+}
+
+#if canImport(XcodeProjectPlugin)
+    import XcodeProjectPlugin
+
+    extension Plugin: XcodeBuildToolPlugin {
+        /// Creates build commands to run SwiftFormat on the target's swift files within an Xcode project.
+        func createBuildCommands(
+            context: XcodePluginContext,
+            target: XcodeTarget,
+        ) throws -> [Command] {
+            try makeCommand(
+                executable: context.tool(named: "swiftformat"),
+                swiftFiles: swiftFiles(from: target),
+                buildEnvironment: createBuildEnvironment(context: context, target: target),
+                pluginWorkDirectory: context.pluginWorkDirectory,
+            )
+        }
+
+        private func createBuildEnvironment(
+            context: XcodePluginContext,
+            target: XcodeTarget,
+        ) throws -> [String: String] {
+            let projectDirectory = context.xcodeProject.directory
+            let swiftFiles = swiftFiles(from: target)
+            let externalSwiftFiles = swiftFiles.filter { !$0.string.hasPrefix("\(projectDirectory)") }
+            guard externalSwiftFiles.isEmpty else {
+                throw PluginError.swiftFilesNotInProjectDirectory(projectDirectory)
+            }
+
+            // When formatting files in an Xcode project, we need to find a common ancestor directory that contains
+            // a .swiftformat file. This ensures that the correct formatting rules are applied to all files.
+            let directories = try swiftFiles.map { try $0.resolveWorkingDirectory(in: projectDirectory) }
+            let workingDirectory = directories.min { $0.depth < $1.depth } ?? projectDirectory
+
+            let filesOutsideWorkingDirectory = swiftFiles.filter { !$0.string.hasPrefix("\(workingDirectory)") }
+            guard filesOutsideWorkingDirectory.isEmpty else {
+                throw PluginError.swiftFilesNotInWorkingDirectory(workingDirectory)
+            }
+
+            // The BUILD_WORKSPACE_DIRECTORY environment variable is used by SwiftFormat to find the configuration file.
+            return ["BUILD_WORKSPACE_DIRECTORY": "\(workingDirectory)"]
+        }
+
+        private func swiftFiles(from target: XcodeTarget) -> [Path] {
+            target.inputFiles.filter { $0.type == .source && $0.path.extension == "swift" }.map(\.path)
+        }
+    }
+#endif

Plugins/SwiftFormatLinterBuildToolPlugin/PluginError.swift

@@ -0,0 +1,49 @@
+//
+//  PluginError.swift
+//  SwiftFormat
+//
+//  Created by Baptiste Clarey Sjöstrand
+//  Copyright 2025 Nick Lockwood
+//
+//  Distributed under the permissive MIT license
+//  Get the latest version from here:
+//
+//  https://github.com/nicklockwood/SwiftFormat
+//
+//  Permission is hereby granted, free of charge, to any person obtaining a copy
+//  of this software and associated documentation files (the "Software"), to deal
+//  in the Software without restriction, including without limitation the rights
+//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+//  copies of the Software, and to permit persons to whom the Software is
+//  furnished to do so, subject to the following conditions:
+//
+//  The above copyright notice and this permission notice shall be included in all
+//  copies or substantial portions of the Software.
+//
+//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+//  SOFTWARE.
+//
+
+import PackagePlugin
+
+enum PluginError: Error, CustomStringConvertible {
+    case pathNotInDirectory(path: Path, directory: Path)
+    case swiftFilesNotInProjectDirectory(Path)
+    case swiftFilesNotInWorkingDirectory(Path)
+
+    var description: String {
+        switch self {
+        case let .pathNotInDirectory(path, directory):
+            "Path '\(path)' is not in directory '\(directory)'."
+        case let .swiftFilesNotInProjectDirectory(directory):
+            "Swift files are not in project directory '\(directory)'."
+        case let .swiftFilesNotInWorkingDirectory(directory):
+            "Swift files are not in working directory '\(directory)'."
+        }
+    }
+}