[DRAFT] Printable regex

Sources/_StringProcessing/Regex/TextualRegex.swift

@@ -0,0 +1,127 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2021-2022 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
+//
+//===----------------------------------------------------------------------===//
+
+@_implementationOnly import _RegexParser
+
+@available(macOS 9999, *) // TODO: 5.9?
+public struct PrintableRegex<Output>: RegexComponent, @unchecked Sendable
+{
+  public var regex: Regex<Output>
+
+  internal var text: String
+
+  public init?(_ re: Regex<Output>) {
+    guard case .convertedRegexLiteral(_, let ast) = re.program.tree.root
+    else {
+      return nil
+    }
+    self.regex = re
+    let str = ast.ast.renderAsCanonical()
+    self.text = str
+  }
+}
+
+
+@available(macOS 9999, *) // TODO: 5.9?
+extension PrintableRegex: Hashable {
+  public static func == (
+    lhs: PrintableRegex<Output>, rhs: PrintableRegex<Output>
+  ) -> Bool {
+    lhs.text == rhs.text
+  }
+  public func hash(into hasher: inout Hasher) {
+    text.hash(into: &hasher)
+  }
+}
+
+// FIXME: Do we only work with ARO as the output type?
+
+@available(macOS 9999, *) // TODO: 5.9?
+extension PrintableRegex: Codable {
+  private init(coding re: Regex<Output>) throws {
+    guard case .convertedRegexLiteral = re.program.tree.root else {
+      throw DecodingError.error
+    }
+    self.regex = re
+    fatalError()
+  }
+
+  private enum DecodingError: Error {
+    case error
+  }
+  enum CodingKeys: CodingKey {
+    case string
+  }
+
+  public init(from decoder: Decoder) throws {
+    let values = try decoder.container(keyedBy: CodingKeys.self)
+    let str = try values.decode(String.self, forKey: .string)
+    guard let pre = try PrintableRegex(Regex(str)) else {
+      throw DecodingError.error
+    }
+    self = pre
+  }
+
+  public func encode(to encoder: Encoder) throws {
+    var container = encoder.container(keyedBy: CodingKeys.self)
+    try container.encode(text, forKey: .string)
+  }
+}
+
+// MARK: - mock API
+
+@available(macOS 9999, *) // TODO: 5.9?
+extension Regex {
+  public var printable: PrintableRegex<Output>? { .init(self) }
+}
+
+@available(macOS 9999, *) // TODO: 5.9?
+public enum RegexSyntax {
+  case swift
+  case pcre2
+  case sql
+  case icu
+  // ...
+}
+
+@available(macOS 9999, *) // TODO: 5.9?
+extension PrintableRegex {
+  public func print(using syntax: RegexSyntax = .swift) -> String {
+    switch syntax {
+    case .swift: return text
+    default: fatalError()
+    }
+  }
+}
+
+@available(macOS 9999, *) // TODO: 5.9?
+extension PrintableRegex: CustomStringConvertible, CustomDebugStringConvertible {
+  public var description: String {
+    text
+  }
+
+  public var debugDescription: String {
+    "/\(text)/"
+  }
+}
+
+
+@available(macOS 9999, *) // TODO: 5.9?
+extension PrintableRegex: LosslessStringConvertible {
+  public init?(_ description: String) {
+    guard let re = try? Regex<Output>(description) else {
+      return nil
+    }
+    self.init(re)
+  }
+
+
+}