Add .swift-format configuration and add a script to format

Author: kateinoigakukun

Diff for: .github/workflows/test.yml

@@ -67,3 +67,18 @@ jobs:
       - run: swift build
         env:
           DEVELOPER_DIR: /Applications/${{ matrix.xcode }}.app/Contents/Developer/
+
+  format:
+    runs-on: ubuntu-latest
+    container:
+      image: swiftwasm/swift:6.0.3
+    steps:
+      - uses: actions/checkout@v4
+      - run: ./Utilities/format.swift
+      - name: Check for formatting changes
+        run: |
+          git config --global --add safe.directory "$GITHUB_WORKSPACE"
+          git diff --exit-code || {
+            echo "::error::The formatting changed some files. Please run \`./Utilities/format.swift\` and commit the changes."
+            exit 1
+          }

Diff for: .swift-format

@@ -0,0 +1,10 @@
+{
+    "version": 1,
+    "lineLength": 120,
+    "indentation": {
+        "spaces": 4
+    },
+    "lineBreakBeforeEachArgument": true,
+    "indentConditionalCompilationBlocks": false,
+    "prioritizeKeepingFunctionOutputTogether": true
+}

Diff for: Utilities/format.swift

@@ -0,0 +1,80 @@
+#!/usr/bin/env swift
+
+import class Foundation.FileManager
+import class Foundation.Process
+import class Foundation.ProcessInfo
+import struct Foundation.URL
+import func Foundation.exit
+
+/// The root directory of the project.
+let projectRoot = URL(fileURLWithPath: #filePath).deletingLastPathComponent().deletingLastPathComponent()
+
+/// Returns the path to the executable if it is found in the PATH environment variable.
+func which(_ executable: String) -> String? {
+    let pathSeparator: Character
+    #if os(Windows)
+    pathSeparator = ";"
+    #else
+    pathSeparator = ":"
+    #endif
+    let paths = ProcessInfo.processInfo.environment["PATH"]!.split(separator: pathSeparator)
+    for path in paths {
+        let url = URL(fileURLWithPath: String(path)).appendingPathComponent(executable)
+        if FileManager.default.isExecutableFile(atPath: url.path) {
+            return url.path
+        }
+    }
+    return nil
+}
+
+/// Runs the `swift-format` command with the given arguments in the project root.
+func swiftFormat(_ arguments: [String]) throws {
+    guard let swiftFormat = which("swift-format") else {
+        print("swift-format not found in PATH")
+        exit(1)
+    }
+    let task = Process()
+    task.executableURL = URL(fileURLWithPath: swiftFormat)
+    task.arguments = arguments
+    task.currentDirectoryURL = projectRoot
+    try task.run()
+    task.waitUntilExit()
+    if task.terminationStatus != 0 {
+        print("swift-format failed with status \(task.terminationStatus)")
+        exit(1)
+    }
+}
+
+/// Patterns to exclude from formatting.
+let excluded: Set<String> = [
+    ".git",
+    ".build",
+    ".index-build",
+    "node_modules",
+    "__Snapshots__",
+    // Exclude the script itself to avoid changing its file mode.
+    URL(fileURLWithPath: #filePath).lastPathComponent,
+]
+
+/// Returns a list of directories to format.
+func filesToFormat() -> [String] {
+    var files: [String] = []
+    let fileManager = FileManager.default
+    let enumerator = fileManager.enumerator(
+        at: projectRoot, includingPropertiesForKeys: nil
+    )!
+    for case let fileURL as URL in enumerator {
+        if excluded.contains(fileURL.lastPathComponent) {
+            if fileURL.hasDirectoryPath {
+                enumerator.skipDescendants()
+            }
+            continue
+        }
+        guard fileURL.pathExtension == "swift" else { continue }
+        files.append(fileURL.path)
+    }
+    return files
+}
+
+// Format the files in the project.
+try swiftFormat(["format", "--parallel", "--in-place", "--recursive"] + filesToFormat())