Add a utility to update the years in license comments of modified files (#1261)

* Add a utility to update the years in license comments of modified files

* Move license updating utility to a dedicated sub directory

* Use `Regex` instead of `NSRegularExpression`

Author: d-ronnqvist

bin/update-license-comments/Package.swift

@@ -0,0 +1,24 @@
+// swift-tools-version: 6.1
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2025 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+import PackageDescription
+
+let package = Package(
+    name: "update-license-for-modified-files",
+    platforms: [
+        .macOS(.v13)
+    ],
+    targets: [
+        .executableTarget(
+            name: "update-license-for-modified-files"
+        ),
+    ]
+)

bin/update-license-comments/Sources/update-license-for-modified-files/main.swift

@@ -0,0 +1,141 @@
+/*
+ This source file is part of the Swift.org open source project
+
+ Copyright (c) 2025 Apple Inc. and the Swift project authors
+ Licensed under Apache License v2.0 with Runtime Library Exception
+
+ See https://swift.org/LICENSE.txt for license information
+ See https://swift.org/CONTRIBUTORS.txt for Swift project authors
+*/
+
+import Foundation
+
+// Determine what changes to consider
+
+enum DiffStrategy {
+    case stagedFiles
+    case comparingTo(treeish: String)
+}
+
+let arguments = ProcessInfo.processInfo.arguments.dropFirst()
+let diffStrategy: DiffStrategy
+switch arguments.first {
+    case "-h", "--help":
+        print("""
+        OVERVIEW: Update the year in the license comment of modified files
+
+        USAGE: swift run update-license-for-modified-files [--staged | <tree-ish>]
+
+        To update the year for staged, but not yet committed files, run:
+            swift run update-license-for-modified-files --staged
+        
+        To update the year for all already committed changes that are different from the 'main' branch, run:
+            swift run update-license-for-modified-files
+        
+        To update the year for the already committed changes in the last commit, run:
+            swift run update-license-for-modified-files HEAD~
+        
+        You can specify any other branch or commit for this argument but I don't know if there's a real use case for doing so.
+        """)
+        exit(0)
+        
+    case nil:
+        diffStrategy = .comparingTo(treeish: "main")
+    case "--staged", "--cached":
+        diffStrategy = .stagedFiles
+    case let treeish?:
+        diffStrategy = .comparingTo(treeish: treeish)
+}
+
+// Find which files are modified
+
+let repoURL: URL = {
+    let url = URL(fileURLWithPath: #filePath)
+        .deletingLastPathComponent() // main.swift
+        .deletingLastPathComponent() // update-license-for-modified-files
+        .deletingLastPathComponent() // Sources
+        .deletingLastPathComponent() // update-license-comments
+        .deletingLastPathComponent() // bin
+    guard FileManager.default.fileExists(atPath: url.appendingPathComponent("Package.swift").path) else {
+        fatalError("The path to the Swift-DocC source root has changed. This should only happen if the 'update-license-comments' sources have moved relative to the Swift-DocC repo.")
+    }
+    return url
+}()
+
+let modifiedFiles = try findModifiedFiles(in: repoURL, strategy: diffStrategy)
+
+// Update the years in the license comment where necessary
+
+//                                        An optional lower range of years for the license comment (including the hyphen)
+//                                        │            The upper range of years for the license comment
+//                                        │            │                The markdown files don't have a "." but the Swift files do
+//                                        │            │                 │                 The markdown files capitalize the P but the Swift files don't
+//                                        │            │                 │                 │
+//                                  ╭─────┴──────╮╭────┴─────╮          ╭┴╮               ╭┴─╮
+let licenseRegex = /Copyright \(c\) (20[0-9]{2}-)?(20[0-9]{2}) Apple Inc\.? and the Swift [Pp]roject authors/
+
+let currentYear = Calendar.current.component(.year, from: .now)
+
+for file in modifiedFiles {
+    guard var content = try? String(contentsOf: file, encoding: .utf8),
+          let licenseMatch = try? licenseRegex.firstMatch(in: content)
+    else {
+        // Didn't encounter a license comment in this file, do nothing
+        continue
+    }
+
+    let upperYearSubstring = licenseMatch.2
+    guard let upperYear = Int(upperYearSubstring) else {
+        print("Couldn't find license year in \(content[licenseMatch.range])")
+        continue
+    }
+    
+    guard upperYear < currentYear else {
+        // The license for this file is already up to date. No need to update it.
+        continue
+    }
+    
+    if licenseMatch.1 == nil {
+        // The existing license comment only contains a single year. Add the new year after
+        content.insert(contentsOf: "-\(currentYear)", at: upperYearSubstring.endIndex)
+    } else {
+        // The existing license comment contains both a start year and an end year. Update the second year.
+        content.replaceSubrange(upperYearSubstring.startIndex ..< upperYearSubstring.endIndex, with: "\(currentYear)")
+    }
+    try content.write(to: file, atomically: true, encoding: .utf8)
+}
+
+// MARK: Modified files
+
+private func findModifiedFiles(in repoURL: URL, strategy: DiffStrategy) throws -> [URL] {
+    let diffCommand = Process()
+    diffCommand.currentDirectoryURL = repoURL
+    diffCommand.executableURL = URL(fileURLWithPath: "/usr/bin/git")
+    
+    let comparisonFlag: String = switch strategy {
+        case .stagedFiles:
+            "--cached"
+        case .comparingTo(let treeish):
+            treeish
+    }
+    
+    diffCommand.arguments = ["diff", "--name-only", comparisonFlag]
+
+    let output = Pipe()
+    diffCommand.standardOutput = output
+    
+    try diffCommand.run()
+    
+    guard let outputData = try output.fileHandleForReading.readToEnd(),
+          let outputString = String(data: outputData, encoding: .utf8)
+    else {
+        return []
+    }
+    
+    return outputString
+        .components(separatedBy: .newlines)
+        .compactMap { line in
+            guard !line.isEmpty else { return nil }
+            return repoURL.appendingPathComponent(line, isDirectory: false)
+        }
+}