Ability To Turn Off Formatting For Subdirectory

README.md

@@ -200,19 +200,24 @@ configuration, by redirecting it to a file and editing it.
 
 ### Configuring the Command Line Tool
 
-For any source file being checked or formatted, `swift-format` looks for a
-JSON-formatted file named `.swift-format` in the same directory. If one is
-found, then that file is loaded to determine the tool's configuration. If the
-file is not found, then it looks in the parent directory, and so on.
+For any source file being checked or formatted, `swift-format` looks for 
+configuration files in the same directory, and parent directories. 
 
-If no configuration file is found, a default configuration is used. The
-settings in the default configuration can be viewed by running
-`swift-format dump-configuration`, which will dump it to standard
-output.
+If it finds a file named `.swift-format-ignore`, its contents will determine
+which files in that directory will be ignored by `swift-format`. Currently
+the only supported option is `*`, which ignores all files.
+
+If it finds a JSON-formatted file called `.swift-format`, then that
+file is loaded to determine the tool's configuration. 
+
+If no configuration file is found at any level, a default configuration 
+is used. The settings in the default configuration can be viewed by
+running `swift-format dump-configuration`, which will dump it to 
+standard output.
 
 If the `--configuration <file>` option is passed to `swift-format`, then that
 configuration will be used unconditionally and the file system will not be
-searched.
+searched for `.swift-format` files.
 
 See [Documentation/Configuration.md](Documentation/Configuration.md) for a
 description of the configuration file format and the settings that are

Sources/SwiftFormat/API/Configuration.swift

@@ -472,17 +472,3 @@ public struct NoAssignmentInExpressionsConfiguration: Codable, Equatable {
 
   public init() {}
 }
-
-fileprivate extension URL {
-  var isRoot: Bool {
-    #if os(Windows)
-    // FIXME: We should call into Windows' native check to check if this path is a root once https://github.com/swiftlang/swift-foundation/issues/976 is fixed.
-    // https://github.com/swiftlang/swift-format/issues/844
-    return self.pathComponents.count <= 1
-    #else
-    // On Linux, we may end up with an string for the path due to https://github.com/swiftlang/swift-foundation/issues/980
-    // TODO: Remove the check for "" once https://github.com/swiftlang/swift-foundation/issues/980 is fixed.
-    return self.path == "/" || self.path == ""
-    #endif
-  }
-}

Sources/SwiftFormat/Utilities/FileIterator.swift

@@ -17,6 +17,11 @@ import Foundation
 @_spi(Internal)
 public struct FileIterator: Sequence, IteratorProtocol {
 
+  /// Name of the ignore file to look for.
+  /// The presence of this file in a directory will cause the formatter
+  /// to skip formatting files in that directory and its subdirectories.
+  fileprivate static let ignoreFileName = ".swift-format-ignore"
+
   /// List of file and directory URLs to iterate over.
   private let urls: [URL]
 
@@ -48,7 +53,7 @@ public struct FileIterator: Sequence, IteratorProtocol {
   /// The given URLs may be files or directories. If they are directories, the iterator will recurse
   /// into them.
   public init(urls: [URL], followSymlinks: Bool) {
-    self.urls = urls
+    self.urls = urls.filter(inputShouldBeProcessed(at:))
     self.urlIterator = self.urls.makeIterator()
     self.followSymlinks = followSymlinks
   }
@@ -83,6 +88,11 @@ public struct FileIterator: Sequence, IteratorProtocol {
           fallthrough
 
         case .typeDirectory:
+          let ignoreFile = next.appendingPathComponent(Self.ignoreFileName)
+          if FileManager.default.fileExists(atPath: ignoreFile.path) {
+            continue
+          }
+
           dirIterator = FileManager.default.enumerator(
             at: next,
             includingPropertiesForKeys: nil,
@@ -169,3 +179,23 @@ private func fileType(at url: URL) -> FileAttributeType? {
   // Linux.
   return try? FileManager.default.attributesOfItem(atPath: url.path)[.type] as? FileAttributeType
 }
+
+/// Returns true if the file should be processed.
+/// Directories are always processed.
+/// Other files are processed if there is not a 
+/// ignore file in the containing directory or any of its parents.
+private func inputShouldBeProcessed(at url: URL) -> Bool {
+  guard fileType(at: url) != .typeDirectory else {
+    return true
+  }
+
+  var containingDirectory = url.absoluteURL.standardized
+  repeat {
+    containingDirectory.deleteLastPathComponent()
+    let candidateFile = containingDirectory.appendingPathComponent(FileIterator.ignoreFileName)
+    if FileManager.default.isReadableFile(atPath: candidateFile.path) {
+      return false
+    }
+  } while !containingDirectory.isRoot
+  return true
+}

Sources/SwiftFormat/Utilities/URL+IsRoot.swift

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2019 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 the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+extension URL {
+  var isRoot: Bool {
+    #if os(Windows)
+    // FIXME: We should call into Windows' native check to check if this path is a root once https://github.com/swiftlang/swift-foundation/issues/976 is fixed.
+    // https://github.com/swiftlang/swift-format/issues/844
+    return self.pathComponents.count <= 1
+    #else
+    // On Linux, we may end up with an string for the path due to https://github.com/swiftlang/swift-foundation/issues/980
+    // TODO: Remove the check for "" once https://github.com/swiftlang/swift-foundation/issues/980 is fixed.
+    return self.path == "/" || self.path == ""
+    #endif
+  }
+}