Multithread processing source files

Previously every source file was formatted / linted one by one. On our
codebase this took a full project format from ~17 minutes to ~5 minutes.

Author: keith

Sources/swift-format/Subcommands/Format.swift

@@ -58,8 +58,8 @@ extension SwiftFormatCommand {
         ) { sourceFile, path, configuration in
           formatMain(
             configuration: configuration, sourceFile: sourceFile, assumingFilename: path,
-            inPlace: inPlace, ignoreUnparsableFiles: formatOptions.ignoreUnparsableFiles,
-            debugOptions: formatOptions.debugOptions, diagnosticEngine: diagnosticEngine)
+            inPlace: self.inPlace, ignoreUnparsableFiles: self.formatOptions.ignoreUnparsableFiles,
+            debugOptions: self.formatOptions.debugOptions, diagnosticEngine: diagnosticEngine)
         }
       }
 

Sources/swift-format/Subcommands/Lint.swift

@@ -43,7 +43,7 @@ extension SwiftFormatCommand {
         ) { sourceFile, path, configuration in
           lintMain(
             configuration: configuration, sourceFile: sourceFile, assumingFilename: path,
-            debugOptions: lintOptions.debugOptions, diagnosticEngine: diagnosticEngine)
+            debugOptions: self.lintOptions.debugOptions, diagnosticEngine: diagnosticEngine)
         }
       }
 

Sources/swift-format/Utilities/Helpers.swift

@@ -42,16 +42,33 @@ func readSource(from fileHandle: FileHandle) -> String? {
 func processSources(
   from paths: [String], configurationPath: String?,
   diagnosticEngine: DiagnosticEngine,
-  transform: (FileHandle, String, Configuration) -> Void
+  transform: @escaping (FileHandle, String, Configuration) -> Void
 ) throws {
+  let concurrentQueue = DispatchQueue(label: "com.queue.Concurrent", qos: .userInitiated, attributes: .concurrent)
+  let group = DispatchGroup()
+  let lock = NSLock()
+  var lastError: Error?
   for path in FileIterator(paths: paths) {
-    guard let sourceFile = FileHandle(forReadingAtPath: path) else {
-      diagnosticEngine.diagnose(
-        Diagnostic.Message(.error, "Unable to create a file handle for source from \(path)."))
-      return
+    concurrentQueue.async(group: group) {
+      guard let sourceFile = FileHandle(forReadingAtPath: path) else {
+        diagnosticEngine.diagnose(
+          Diagnostic.Message(.error, "Unable to create a file handle for source from \(path)."))
+        return
+      }
+      do {
+        let configuration = try loadConfiguration(forSwiftFile: path, configFilePath: configurationPath)
+        transform(sourceFile, path, configuration)
+      } catch let error {
+        lock.lock()
+        lastError = error
+        lock.unlock()
+      }
     }
-    let configuration = try loadConfiguration(forSwiftFile: path, configFilePath: configurationPath)
-    transform(sourceFile, path, configuration)
+  }
+
+  group.wait()
+  if let error = lastError {
+    throw error
   }
 }