Add dump-effective-configuration subcommand

README.md

@@ -210,13 +210,19 @@ 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.
+If the `--configuration <configuration>` option is passed to `swift-format`,
+then that configuration will be used unconditionally and the file system will
+not be searched.
 
 See [Documentation/Configuration.md](Documentation/Configuration.md) for a
-description of the configuration file format and the settings that are
-available.
+description of the configuration format and the settings that are available.
+
+#### Viewing the Effective Configuration
+
+The `dump-configuration` subcommand accepts a `--effective` flag. If set, it
+dumps the configuration that would be used if `swift-format` was executed from
+the current working directory, and accounts for `.swift-format` files or
+ `--configuration` options as outlined above.
 
 ### Miscellaneous
 

Sources/SwiftFormat/API/Configuration+Dump.swift

@@ -0,0 +1,35 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 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 the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+import Foundation
+
+extension Configuration {
+  /// Return the configuration as a JSON string.
+  public func asJsonString() throws -> String {
+    let data: Data
+
+    do {
+      let encoder = JSONEncoder()
+      encoder.outputFormatting = [.prettyPrinted, .sortedKeys]
+      data = try encoder.encode(self)
+    } catch {
+      throw SwiftFormatError.configurationDumpFailed("\(error)")
+    }
+
+    guard let jsonString = String(data: data, encoding: .utf8) else {
+      // This should never happen, but let's make sure we fail more gracefully than crashing, just in case.
+      throw SwiftFormatError.configurationDumpFailed("The JSON was not valid UTF-8")
+    }
+
+    return jsonString
+  }
+}

Sources/SwiftFormat/API/SwiftFormatError.swift

@@ -28,6 +28,9 @@ public enum SwiftFormatError: LocalizedError {
   /// The requested experimental feature name was not recognized by the parser.
   case unrecognizedExperimentalFeature(String)
 
+  /// An error happened while dumping the tool's configuration.
+  case configurationDumpFailed(String)
+
   public var errorDescription: String? {
     switch self {
     case .fileNotReadable:
@@ -38,6 +41,8 @@ public enum SwiftFormatError: LocalizedError {
       return "file contains invalid Swift syntax"
     case .unrecognizedExperimentalFeature(let name):
       return "experimental feature '\(name)' was not recognized by the Swift parser"
+    case .configurationDumpFailed(let message):
+      return "dumping configuration failed: \(message)"
     }
   }
 }

Sources/SwiftFormat/CMakeLists.txt

@@ -1,14 +1,15 @@
 #[[
 This source file is part of the swift-format open source project
 
-Copyright (c) 2024 Apple Inc. and the swift-format project authors
+Copyright (c) 2024 - 2025 Apple Inc. and the swift-format project authors
 Licensed under Apache License v2.0 with Runtime Library Exception
 
 See https://swift.org/LICENSE.txt for license information
 #]]
 
 add_library(SwiftFormat
   API/Configuration+Default.swift
+  API/Configuration+Dump.swift
   API/Configuration.swift
   API/DebugOptions.swift
   API/Finding.swift

Sources/swift-format/CMakeLists.txt

@@ -1,7 +1,7 @@
 #[[
 This source file is part of the swift-format open source project
 
-Copyright (c) 2024 Apple Inc. and the swift-format project authors
+Copyright (c) 2024 - 2025 Apple Inc. and the swift-format project authors
 Licensed under Apache License v2.0 with Runtime Library Exception
 
 See https://swift.org/LICENSE.txt for license information
@@ -15,6 +15,7 @@ add_executable(swift-format
   Frontend/FormatFrontend.swift
   Frontend/Frontend.swift
   Frontend/LintFrontend.swift
+  Subcommands/ConfigurationOptions.swift
   Subcommands/DumpConfiguration.swift
   Subcommands/Format.swift
   Subcommands/Lint.swift
@@ -23,7 +24,6 @@ add_executable(swift-format
   Utilities/Diagnostic.swift
   Utilities/DiagnosticsEngine.swift
   Utilities/FileHandleTextOutputStream.swift
-  Utilities/FormatError.swift
   Utilities/StderrDiagnosticPrinter.swift
   Utilities/TTY.swift)
 target_link_libraries(swift-format PRIVATE

Sources/swift-format/Frontend/FormatFrontend.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2024 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 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
@@ -20,9 +20,9 @@ class FormatFrontend: Frontend {
   /// Whether or not to format the Swift file in-place.
   private let inPlace: Bool
 
-  init(lintFormatOptions: LintFormatOptions, inPlace: Bool) {
+  init(configurationOptions: ConfigurationOptions, lintFormatOptions: LintFormatOptions, inPlace: Bool) {
     self.inPlace = inPlace
-    super.init(lintFormatOptions: lintFormatOptions)
+    super.init(configurationOptions: configurationOptions, lintFormatOptions: lintFormatOptions)
   }
 
   override func processFile(_ fileToProcess: FileToProcess) {