SwiftFormat/Sources/CommandLine.swift

//
//  CommandLine.swift
//  SwiftFormat
//
//  Created by Nick Lockwood on 10/01/2017.
//  Copyright 2017 Nick Lockwood
//
//  Distributed under the permissive MIT license
//  Get the latest version from here:
//
//  https://github.com/nicklockwood/SwiftFormat
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
//  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//  SOFTWARE.
//

import Foundation

/// Public interface for the SwiftFormat command-line functions
public struct CLI {
    /// Output type for printed content
    public enum OutputType {
        case info
        case success
        case error
        case warning
        case content
    }

    /// Output handler - override this to intercept output from the CLI
    public static var print: (String, OutputType) -> Void = { _, _ in
        fatalError("No print hook set")
    }

    /// Input handler - override this to inject input into the CLI
    /// Injected lines should include the terminating newline character
    public static var readLine: () -> String? = {
        Swift.readLine(strippingNewline: false)
    }

    /// Run the CLI with the specified input arguments
    public static func run(in directory: String, with args: [String] = CommandLine.arguments) -> ExitCode {
        return processArguments(args, in: directory)
    }

    /// Run the CLI with the specified input string (this will be parsed into multiple arguments)
    public static func run(in directory: String, with argumentString: String) -> ExitCode {
        return run(in: directory, with: parseArguments(argumentString))
    }
}

private func print(_ message: String, as type: CLI.OutputType = .info) {
    CLI.print(message, type)
}

func printWarnings(_ errors: [Error]) {
    for error in errors {
        print("warning: \(error)", as: .warning)
    }
}

// Represents the exit codes to the command line. See `man sysexits` for more information.
public enum ExitCode: Int32 {
    case ok = 0 // EX_OK
    case lintFailure = 1
    case error = 70 // EX_SOFTWARE
}

func printHelp() {
    print("""

    swiftformat, version \(version)
    copyright (c) 2016 Nick Lockwood

    --help             print this help page
    --version          print the currently installed swiftformat version

    swiftformat can operate on file & directories, or directly on input from stdin:

    usage: swiftformat [<file> <file> ...] [--inferoptions] [--output path] [...]

    <file> <file> ...  one or more swift files or directory paths to be processed

    --config           path to a configuration file containing rules and options
    --inferoptions     instead of formatting input, use it to infer format options
    --output           output path for formatted file(s) (defaults to input path)
    --exclude          list of file or directory paths to ignore (comma-delimited)
    --symlinks         how symlinks are handled. "follow" or "ignore" (default)
    --fragment         input is part of a larger file. "true" or "false" (default)
    --conflictmarkers  merge conflict markers, either "reject" (default) or "ignore"
    --cache            path to cache file, or "clear" or "ignore" the default cache
    --verbose          display detailed formatting output and warnings/errors
    --dryrun           run in "dry" mode (without actually changing any files)
    --lint             returns non-zero exit code if files would be changed

    swiftformat has a number of rules that can be enabled or disabled. by default
    most rules are enabled. use --rules to display all enabled/disabled rules:

    --rules            the list of rules to apply (pass nothing to print all rules)
    --disable          a list of format rules to be disabled (comma-delimited)
    --enable           a list of disabled rules to be re-enabled (comma-delimited)
    --experimental     experimental rules. "enabled" or "disabled" (default)

    swiftformat's rules can be configured using options. a given option may affect
    multiple rules. options have no affect if the related rules have been disabled:

    --allman           use allman indentation style. "true" or "false" (default)
    --binarygrouping   binary grouping,threshold (default: 4,8) or "none", "ignore"
    --commas           commas in collection literals. "always" (default) or "inline"
    --comments         indenting of comment bodies. "indent" (default) or "ignore"
    --decimalgrouping  decimal grouping,threshold (default: 3,6) or "none", "ignore"
    --elseposition     placement of else/catch. "same-line" (default) or "next-line"
    --empty            how empty values are represented. "void" (default) or "tuple"
    --exponentcase     case of 'e' in numbers. "lowercase" or "uppercase" (default)
    --exponentgrouping group exponent digits, "enabled" or "disabled" (default)
    --fractiongrouping group digits after '.', "enabled" or "disabled" (default)
    --header           header comments. "strip", "ignore", or the text you wish use
    --hexgrouping      hex grouping,threshold (default: 4,8) or "none", "ignore"
    --hexliteralcase   casing for hex literals. "uppercase" (default) or "lowercase"
    --ifdef            #if indenting. "indent" (default), "noindent" or "outdent"
    --indent           number of spaces to indent, or "tab" to use tabs
    --indentcase       indent cases inside a switch. "true" or "false" (default)
    --linebreaks       linebreak character to use. "cr", "crlf" or "lf" (default)
    --octalgrouping    octal grouping,threshold or "none", "ignore". default: 4,8
    --operatorfunc     spacing for operator funcs. "spaced" (default) or "nospace"
    --patternlet       let/var placement in patterns. "hoist" (default) or "inline"
    --ranges           spacing for ranges. "spaced" (default) or "nospace"
    --semicolons       allow semicolons. "never" or "inline" (default)
    --self             use self for member variables. "remove" (default) or "insert"
    --stripunusedargs  "closure-only", "unnamed-only" or "always" (default)
    --trimwhitespace   trim trailing space. "always" (default) or "nonblank-lines"
    --wraparguments    wrap function args. "beforefirst", "afterfirst", "preserve"
    --wrapcollections  wrap array/dict. "beforefirst", "afterfirst", "preserve"

    """)
}

func expandPath(_ path: String, in directory: String) -> URL {
    if path.hasPrefix("/") {
        return URL(fileURLWithPath: path)
    }
    if path.hasPrefix("~") {
        return URL(fileURLWithPath: NSString(string: path).expandingTildeInPath)
    }
    return URL(fileURLWithPath: directory).appendingPathComponent(path)
}

func timeEvent(block: () throws -> Void) rethrows -> String {
    let start = CFAbsoluteTimeGetCurrent()
    try block()
    let time = round((CFAbsoluteTimeGetCurrent() - start) * 100) / 100 // round to nearest 10ms
    return String(format: "%gs", time)
}

func parseArguments(_ argumentString: String) -> [String] {
    var arguments = [""] // Arguments always begin with script path
    var characters = String.UnicodeScalarView.SubSequence(argumentString.unicodeScalars)
    var string = ""
    var escaped = false
    var quoted = false
    while let char = characters.popFirst() {
        switch char {
        case "\\" where !escaped:
            escaped = true
        case "\"" where !escaped && !quoted:
            quoted = true
        case "\"" where !escaped && quoted:
            quoted = false
            fallthrough
        case " " where !escaped && !quoted:
            if !string.isEmpty {
                arguments.append(string)
            }
            string.removeAll()
        case "\"" where escaped:
            escaped = false
            string.append("\"")
        case _ where escaped && quoted:
            string.append("\\")
            fallthrough
        default:
            escaped = false
            string.append(Character(char))
        }
    }
    if !string.isEmpty {
        arguments.append(string)
    }
    return arguments
}

private let allRules = Set(FormatRules.byName.keys)
func parseRules(_ rules: String) throws -> [String] {
    return try rules.components(separatedBy: ",").compactMap {
        let name = $0.trimmingCharacters(in: .whitespacesAndNewlines)
        if name.isEmpty {
            return nil
        } else if !allRules.contains(name) {
            throw FormatError.options("unknown rule '\(name)'")
        }
        return name
    }
}

func mergeArguments(_ args: [String: String], into config: [String: String]) throws -> [String: String] {
    var input = config
    var output = args
    // Merge rules
    if let rules = try output["rules"].map(parseRules) {
        if rules.isEmpty {
            output["rules"] = nil
        } else {
            input["rules"] = nil
            input["enable"] = nil
            input["disable"] = nil
        }
    } else {
        if let _disable = try output["disable"].map(parseRules) {
            if let rules = try input["rules"].map(parseRules) {
                input["rules"] = Set(rules).subtracting(_disable).joined(separator: ",")
            }
            if let enable = try input["enable"].map(parseRules) {
                input["enable"] = Set(enable).subtracting(_disable).joined(separator: ",")
            }
            if let disable = try input["disable"].map(parseRules) {
                input["disable"] = Set(disable).union(_disable).joined(separator: ",")
                output["disable"] = nil
            }
        }
        if let _enable = try args["enable"].map(parseRules) {
            if let enable = try input["enable"].map(parseRules) {
                input["enable"] = Set(enable).union(_enable).joined(separator: ",")
                output["enable"] = nil
            }
            if let disable = try input["disable"].map(parseRules) {
                input["disable"] = Set(disable).subtracting(_enable).joined(separator: ",")
            }
        }
    }
    // Merge other arguments
    for (key, value) in input where output[key] == nil {
        output[key] = value
    }
    return output
}

func processArguments(_ args: [String], in directory: String) -> ExitCode {
    var errors = [Error]()
    var verbose = false
    var dryrun = false
    var lint = false
    do {
        // Get arguments
        var args = try preprocessArguments(args, commandLineArguments)

        // Show help
        if args["help"] != nil {
            printHelp()
            return .ok
        }

        // Show version
        if args["version"] != nil {
            print("swiftformat, version \(version)")
            return .ok
        }

        // Display rules (must be checked before merging config)
        let showRules = (args["rules"] == "")

        // Config file
        if let configURL = args["config"].map({ expandPath($0, in: directory) }) {
            if args["config"] == "" {
                throw FormatError.options("--config argument expects a value")
            }
            if !FileManager.default.fileExists(atPath: configURL.path) {
                throw FormatError.reading("specified config file does not exist: \(configURL.path)")
            }
            let data: Data
            do {
                data = try Data(contentsOf: configURL)
            } catch let error {
                throw FormatError.reading("failed to read config file at \(configURL.path), \(error)")
            }
            let config = try parseConfigFile(data)
            args = try mergeArguments(args, into: config)
        }

        // Rules
        var rules = allRules.subtracting(FormatRules.disabledByDefault)
        if let names = try args["rules"].map(parseRules), !names.isEmpty {
            rules = Set(names)
        }
        if let names = try args["enable"].map(parseRules) {
            if names.isEmpty {
                throw FormatError.options("--enable argument expects a value")
            }
            rules.formUnion(names)
        }
        if let names = try args["disable"].map(parseRules) {
            if names.isEmpty {
                throw FormatError.options("--disable argument expects a value")
            }
            rules.subtract(names)
        }
        if showRules {
            print("")
            for name in Array(allRules).sorted() {
                print(" \(name)\(rules.contains(name) ? "" : " (disabled)")")
            }
            print("")
            return .ok
        }

        // Options
        let formatOptions = try formatOptionsFor(args) ?? .default
        let fileOptions = try fileOptionsFor(args)

        // Input path(s)
        var inputURLs = [URL]()
        while let inputPath = args[String(inputURLs.count + 1)] {
            inputURLs.append(expandPath(inputPath, in: directory))
        }

        // Verbose
        if let arg = args["verbose"] {
            verbose = true
            if !arg.isEmpty {
                // verbose doesn't take an argument, so treat argument as another input path
                inputURLs.append(expandPath(arg, in: directory))
            }
            if inputURLs.isEmpty, args["output"] ?? "" != "" {
                throw FormatError.options("--verbose option has no effect unless an output file is specified")
            }
        }

        // Dry run
        if let arg = args["dryrun"] {
            dryrun = true
            if !arg.isEmpty {
                // dryrun doesn't take an argument, so treat argument as another input path
                inputURLs.append(expandPath(arg, in: directory))
            }
        }

        // Lint
        if let arg = args["lint"] {
            dryrun = true
            lint = true
            if !arg.isEmpty {
                // lint doesn't take an argument, so treat argument as another input path
                inputURLs.append(expandPath(arg, in: directory))
            }
        }

        // Excluded path(s)
        var excludedURLs = [URL]()
        if let arg = args["exclude"] {
            if inputURLs.isEmpty {
                throw FormatError.options("--exclude option has no effect unless an input path is specified")
            }
            for path in arg.components(separatedBy: ",") {
                excludedURLs.append(expandPath(path, in: directory))
            }
        }

        // Infer options
        if let arg = args["inferoptions"] {
            guard args["config"] == nil else {
                throw FormatError.options("--inferoptions option can't be used along with a config file")
            }
            if !arg.isEmpty {
                // inferoptions doesn't take an argument, so treat argument as another input path
                inputURLs.append(expandPath(arg, in: directory))
            }
            if inputURLs.count > 0 {
                print("inferring swiftformat options from source file(s)...")
                var filesParsed = 0, options = FormatOptions.default, errors = [Error]()
                let time = timeEvent {
                    (filesParsed, options, errors) = inferOptions(from: inputURLs, excluding: excludedURLs)
                }
                printWarnings(errors)
                if filesParsed == 0 {
                    throw FormatError.parsing("failed to to infer options")
                }
                var filesChecked = filesParsed
                for case let error as FormatError in errors {
                    switch error {
                    case .parsing, .reading:
                        filesChecked += 1
                    case .writing:
                        assertionFailure()
                    case .options:
                        break
                    }
                }
                print("options inferred from \(filesParsed)/\(filesChecked) files in \(time)")
                print("")
                print(commandLineArguments(for: options).map({ "--\($0.key) \($0.value)" }).joined(separator: " "))
                print("")
                return .ok
            }
        }

        // Output path
        let outputURL = args["output"].map { expandPath($0, in: directory) }
        if outputURL != nil {
            if args["output"] == "" {
                throw FormatError.options("--output argument expects a value")
            } else if inputURLs.count > 1 {
                throw FormatError.options("--output argument is only valid for a single input file")
            }
        }

        // Cache path
        var cacheURL: URL?
        let defaultCacheFileName = "swiftformat.cache"
        let manager = FileManager.default
        func setDefaultCacheURL() {
            if let cachePath =
                NSSearchPathForDirectoriesInDomains(.cachesDirectory, .userDomainMask, true).first {
                let cacheDirectory = URL(fileURLWithPath: cachePath).appendingPathComponent("com.charcoaldesign.swiftformat")
                do {
                    try manager.createDirectory(at: cacheDirectory, withIntermediateDirectories: true, attributes: nil)
                    cacheURL = cacheDirectory.appendingPathComponent(defaultCacheFileName)
                } catch {
                    errors.append(FormatError.writing("failed to create cache directory at \(cacheDirectory.path)"))
                }
            } else {
                errors.append(FormatError.reading("failed to find cache directory at ~/Library/Caches"))
            }
        }
        if let cache = args["cache"] {
            switch cache {
            case "":
                throw FormatError.options("--cache option expects a value")
            case "ignore":
                break
            case "clear":
                setDefaultCacheURL()
                if let cacheURL = cacheURL, manager.fileExists(atPath: cacheURL.path) {
                    do {
                        try manager.removeItem(at: cacheURL)
                    } catch {
                        errors.append(FormatError.writing("failed to delete cache file at \(cacheURL.path)"))
                    }
                }
            default:
                cacheURL = expandPath(cache, in: directory)
                guard cacheURL != nil else {
                    throw FormatError.options("unsupported --cache value `\(cache)`")
                }
                var isDirectory: ObjCBool = false
                if manager.fileExists(atPath: cacheURL!.path, isDirectory: &isDirectory) && isDirectory.boolValue {
                    cacheURL = cacheURL!.appendingPathComponent(defaultCacheFileName)
                }
            }
        } else {
            setDefaultCacheURL()
        }

        // If no input file, try stdin
        if inputURLs.count == 0 {
            var input: String?
            var finished = false
            var fatalError: Error?
            DispatchQueue.global(qos: .userInitiated).async {
                while let line = CLI.readLine() {
                    input = (input ?? "") + line
                }
                if let input = input {
                    do {
                        if args["inferoptions"] != nil {
                            let tokens = tokenize(input)
                            let options = inferOptions(from: tokens)
                            print(commandLineArguments(for: options).map({ "--\($0.key) \($0.value)" }).joined(separator: " "))
                        } else if let outputURL = outputURL {
                            print("running swiftformat...")
                            if dryrun {
                                print("(dryrun mode - no files will be changed)", as: .warning)
                            }
                            let output = try format(input,
                                                    ruleNames: Array(rules),
                                                    options: formatOptions,
                                                    verbose: verbose)
                            if (try? String(contentsOf: outputURL)) != output {
                                if dryrun {
                                    print("would have updated \(outputURL.path)", as: .info)
                                } else {
                                    do {
                                        try output.write(to: outputURL, atomically: true, encoding: .utf8)
                                    } catch {
                                        throw FormatError.writing("failed to write file \(outputURL.path)")
                                    }
                                }
                            }
                            print("swiftformat completed successfully", as: .success)
                        } else {
                            // Write to stdout
                            let output = try format(input,
                                                    ruleNames: Array(rules),
                                                    options: formatOptions,
                                                    verbose: false)
                            print(output, as: .content)
                        }
                    } catch {
                        fatalError = error
                    }
                }
                finished = true
            }
            // Wait for input
            let start = NSDate()
            while start.timeIntervalSinceNow > -0.01 {}
            // If no input received by now, assume none is coming
            if input != nil {
                while !finished && start.timeIntervalSinceNow > -30 {}
                if let fatalError = fatalError {
                    throw fatalError
                }
            } else if args["inferoptions"] != nil {
                throw FormatError.options("--inferoptions requires one or more input files")
            } else {
                printHelp()
            }
            return .ok
        }

        print("running swiftformat...")
        if dryrun {
            print("(dryrun mode - no files will be changed)", as: .warning)
        }

        // Format the code
        var filesWritten = 0, filesFailed = 0, filesChecked = 0
        let time = timeEvent {
            var _errors = [Error]()
            (filesWritten, filesFailed, filesChecked, _errors) = processInput(inputURLs,
                                                                              excluding: excludedURLs,
                                                                              andWriteToOutput: outputURL,
                                                                              withRules: Array(rules),
                                                                              formatOptions: formatOptions,
                                                                              fileOptions: fileOptions,
                                                                              verbose: verbose,
                                                                              dryrun: dryrun,
                                                                              cacheURL: cacheURL)
            errors += _errors
        }

        if filesWritten == 0 {
            if filesChecked == 0 {
                if let error = errors.first {
                    errors.removeAll()
                    throw error
                }
                let inputPaths = inputURLs.map({ $0.path }).joined(separator: ", ")
                throw FormatError.options("no eligible files found at \(inputPaths)")
            } else if !dryrun && !errors.isEmpty {
                throw FormatError.options("failed to format any files")
            }
        }
        if verbose {
            print("")
        }
        printWarnings(errors)
        if dryrun {
            let result = "swiftformat completed. \(filesFailed)/\(filesChecked) files would have been updated in \(time)"
            if lint && filesFailed > 0 {
                print(result, as: .error)
                return .lintFailure
            } else {
                print(result, as: .success)
            }
        } else {
            print("swiftformat completed. \(filesWritten)/\(filesChecked) files updated in \(time)", as: .success)
        }
        return .ok
    } catch {
        if !verbose {
            // Warnings would be redundant at this point
            printWarnings(errors)
        }
        // Fatal error
        print("error: \(error)", as: .error)
        return .error
    }
}

func inferOptions(from inputURLs: [URL], excluding excludedURLs: [URL]) -> (Int, FormatOptions, [Error]) {
    var tokens = [Token]()
    var errors = [Error]()
    var filesParsed = 0
    for inputURL in inputURLs {
        errors += enumerateFiles(withInputURL: inputURL, excluding: excludedURLs) { inputURL, _ in
            guard let input = try? String(contentsOf: inputURL) else {
                throw FormatError.reading("failed to read file \(inputURL.path)")
            }
            let _tokens = tokenize(input)
            return {
                filesParsed += 1
                tokens += _tokens
            }
        }
    }
    return (filesParsed, inferOptions(from: tokens), errors)
}

func format(_ source: String,
            ruleNames: [String],
            options: FormatOptions,
            verbose: Bool) throws -> String {
    // Parse source
    let originalTokens = tokenize(source)
    var tokens = originalTokens

    // Apply rules
    let rulesByName = FormatRules.byName
    let ruleNames = ruleNames.sorted()
    let rules = ruleNames.compactMap { rulesByName[$0] }
    var rulesApplied = Set<String>()
    let callback: ((Int, [Token]) -> Void)? = verbose ? { i, updatedTokens in
        if updatedTokens != tokens {
            rulesApplied.insert(ruleNames[i])
            tokens = updatedTokens
        }
    } : nil
    tokens = try applyRules(rules, to: tokens, with: options, callback: callback)

    // Display info
    if verbose {
        if rulesApplied.isEmpty || tokens == originalTokens {
            print(" -- no changes", as: .success)
        } else {
            let sortedNames = Array(rulesApplied).sorted().joined(separator: ", ")
            print(" -- rules applied: \(sortedNames)", as: .success)
        }
    }

    // Output
    return sourceCode(for: tokens)
}

func processInput(_ inputURLs: [URL],
                  excluding excludedURLs: [URL],
                  andWriteToOutput outputURL: URL?,
                  withRules enabled: [String],
                  formatOptions: FormatOptions,
                  fileOptions: FileOptions,
                  verbose: Bool,
                  dryrun: Bool,
                  cacheURL: URL?) -> (Int, Int, Int, [Error]) {
    // Filter rules
    var disabled = [String]()
    for name: String in FormatRules.byName.keys {
        if !enabled.contains(name) {
            disabled.append(name)
        }
    }
    let ruleNames = enabled.count <= disabled.count ?
        (enabled.count == 0 ? "" : "rules:\(enabled.joined(separator: ","));") :
        (disabled.count == 0 ? "" : "disabled:\(disabled.joined(separator: ","));")
    // Load cache
    let cachePrefix = "\(version);\(formatOptions)\(ruleNames)"
    let cacheDirectory = cacheURL?.deletingLastPathComponent().absoluteURL
    var cache: [String: String]?
    if let cacheURL = cacheURL {
        cache = NSDictionary(contentsOf: cacheURL) as? [String: String] ?? [:]
    }
    // Format files
    var errors = [Error]()
    var filesChecked = 0, filesFailed = 0, filesWritten = 0
    for inputURL in inputURLs {
        errors += enumerateFiles(withInputURL: inputURL,
                                 excluding: excludedURLs,
                                 outputURL: outputURL,
                                 options: fileOptions,
                                 concurrent: !verbose) { inputURL, outputURL in

            guard let input = try? String(contentsOf: inputURL) else {
                throw FormatError.reading("failed to read file \(inputURL.path)")
            }
            let cacheKey: String = {
                var path = inputURL.absoluteURL.path
                if let cacheDirectory = cacheDirectory {
                    let commonPrefix = path.commonPrefix(with: cacheDirectory.path)
                    path = String(path[commonPrefix.endIndex ..< path.endIndex])
                }
                return path
            }()
            do {
                if verbose {
                    print("formatting \(inputURL.path)")
                }
                let output: String
                if cache?[cacheKey] == cachePrefix + String(input.count) {
                    output = input
                    if verbose {
                        print("-- no changes", as: .success)
                    }
                } else {
                    output = try format(input, ruleNames: enabled, options: formatOptions, verbose: verbose)
                }
                if outputURL != inputURL, (try? String(contentsOf: outputURL)) != output {
                    if !dryrun {
                        do {
                            try FileManager.default.createDirectory(at: outputURL.deletingLastPathComponent(),
                                                                    withIntermediateDirectories: true,
                                                                    attributes: nil)
                        } catch {
                            throw FormatError.writing("failed to create directory at \(outputURL.path), \(error)")
                        }
                    }
                } else if output == input {
                    // No changes needed
                    return {
                        filesChecked += 1
                        cache?[cacheKey] = cachePrefix + String(output.count)
                    }
                }
                if dryrun {
                    print("would have updated \(outputURL.path)", as: .info)
                    return {
                        filesChecked += 1
                        filesFailed += 1
                    }
                } else {
                    do {
                        if verbose {
                            print("writing \(outputURL.path)", as: .info)
                        }
                        try output.write(to: outputURL, atomically: true, encoding: .utf8)
                        return {
                            filesChecked += 1
                            filesFailed += 1
                            filesWritten += 1
                            cache?[cacheKey] = cachePrefix + String(output.count)
                        }
                    } catch {
                        throw FormatError.writing("failed to write file \(outputURL.path), \(error)")
                    }
                }
            } catch {
                if verbose {
                    print("-- error: \(error)", as: .error)
                }
                return {
                    filesChecked += 1
                    if case let FormatError.parsing(string) = error {
                        throw FormatError.parsing("\(string) in \(inputURL.path)")
                    }
                    throw error
                }
            }
        }
    }
    if verbose {
        var errorCount = errors.count
        errors = errors.filter { error in
            guard let error = error as? FormatError else {
                return true
            }
            switch error {
            case .options, .reading:
                return true
            case .parsing, .writing:
                return false
            }
        }
        errorCount -= errors.count
        if errorCount > 0 {
            // Replace individual warnings with a generic message, to avoid repetition
            errors.append(FormatError.writing("\(errorCount) file\(errorCount == 1 ? "" : "s") could not be formatted"))
        }
    }
    if filesChecked > 0 {
        // Save cache
        if let cache = cache, let cacheURL = cacheURL, let cacheDirectory = cacheDirectory {
            if !(cache as NSDictionary).write(to: cacheURL, atomically: true) {
                if FileManager.default.fileExists(atPath: cacheDirectory.path) {
                    errors.append(FormatError.writing("failed to write cache file at \(cacheURL.path)"))
                } else {
                    errors.append(FormatError.reading("specified cache file directory does not exist: \(cacheDirectory.path)"))
                }
            }
        }
    }
    return (filesWritten, filesFailed, filesChecked, errors)
}

func preprocessArguments(_ args: [String], _ names: [String]) throws -> [String: String] {
    var anonymousArgs = 0
    var namedArgs: [String: String] = [:]
    var name = ""
    for arg in args {
        if arg.hasPrefix("--") {
            // Long argument names
            let key = String(arg.unicodeScalars.dropFirst(2))
            if !names.contains(key) {
                throw FormatError.options("unknown option --\(key)")
            }
            name = key
            namedArgs[name] = ""
            continue
        } else if arg.hasPrefix("-") {
            // Short argument names
            let flag = String(arg.unicodeScalars.dropFirst())
            let matches = names.filter { $0.hasPrefix(flag) }
            if matches.count > 1 {
                throw FormatError.options("ambiguous flag -\(flag)")
            } else if matches.count == 0 {
                throw FormatError.options("unknown flag -\(flag)")
            } else {
                name = matches[0]
                namedArgs[name] = ""
            }
            continue
        }
        if name == "" {
            // Argument is anonymous
            name = String(anonymousArgs)
            anonymousArgs += 1
        }
        namedArgs[name] = arg
        name = ""
    }
    return namedArgs
}

func parseConfigFile(_ data: Data) throws -> [String: String] {
    guard let input = String(data: data, encoding: .utf8) else {
        throw FormatError.reading("unable to read data for configuration file")
    }
    let lines = input.components(separatedBy: .newlines)
    let arguments = try lines.flatMap { line -> [String] in
        let parts = line.components(separatedBy: .whitespaces).filter { !$0.isEmpty }
        if let key = parts.first, !key.hasPrefix("-") {
            throw FormatError.options("unknown option \(key)")
        }
        return parts
    }
    return try preprocessArguments(arguments, commandLineArguments)
}

/// Get command line arguments for formatting options
/// (excludes non-formatting options and deprecated/renamed options)
func commandLineArguments(for options: FormatOptions, excludingDefaults: Bool = false) -> [String: String] {
    var args = [String: String]()
    for descriptor in FormatOptions.Descriptor.formatting where !descriptor.isDeprecated {
        let value = descriptor.fromOptions(options)
        if !excludingDefaults || value != descriptor.fromOptions(.default) {
            args[descriptor.argumentName] = value
        }
    }
    return args
}

private func processOption(_ key: String,
                           in args: [String: String],
                           from: inout Set<String>,
                           handler: (String) throws -> Void) throws {
    precondition(commandLineArguments.contains(key))
    var arguments = from
    arguments.remove(key)
    from = arguments
    guard let value = args[key] else {
        return
    }
    guard !value.isEmpty else {
        throw FormatError.options("--\(key) option expects a value")
    }
    do {
        try handler(value)
    } catch {
        throw FormatError.options("unsupported --\(key) value '\(value)'")
    }
}

/// Parse FileOptions from arguments
func fileOptionsFor(_ args: [String: String]) throws -> FileOptions {
    var options = FileOptions()
    var arguments = Set(fileArguments)
    try processOption("symlinks", in: args, from: &arguments) {
        switch $0.lowercased() {
        case "follow":
            options.followSymlinks = true
        case "ignore":
            options.followSymlinks = false
        default:
            throw FormatError.options("")
        }
    }
    assert(arguments.isEmpty, "\(arguments.joined(separator: ","))")
    return options
}

/// Parse FormatOptions from arguments
/// Returns nil if the arguments dictionary does not contain any formatting arguments
func formatOptionsFor(_ args: [String: String]) throws -> FormatOptions? {
    var options = FormatOptions.default
    var arguments = Set(formattingArguments)

    var containsFormatOption = false
    for option in FormatOptions.Descriptor.all {
        var handler = option.toOptions
        if let message = option.deprecationMessage {
            handler = { string, options in
                print(message, as: .warning)
                try option.toOptions(string, &options)
            }
        }
        try processOption(option.argumentName, in: args, from: &arguments) {
            containsFormatOption = true
            try handler($0, &options)
        }
    }
    assert(arguments.isEmpty, "\(arguments.joined(separator: ","))")
    return containsFormatOption ? options : nil
}

let fileArguments = [
    // File options
    "symlinks",
]

let formattingArguments = FormatOptions.Descriptor.formatting.map { $0.argumentName }
let internalArguments = FormatOptions.Descriptor.internal.map { $0.argumentName }

let commandLineArguments = [
    // File options
    "config",
    "inferoptions",
    "output",
    "exclude",
    "cache",
    "verbose",
    "dryrun",
    "lint",
    // Rules
    "disable",
    "enable",
    "rules",
    // Misc
    "help",
    "version",
] + fileArguments + formattingArguments + internalArguments

let deprecatedArguments = FormatOptions.Descriptor.all.compactMap {
    $0.isDeprecated ? $0.argumentName : nil
}