Merge pull request #63048 from lorentey/fix-String-debugDescription

[stdlib] String.debugDescription: Fix quoting behavior

Author: lorentey

stdlib/public/core/String.swift

@@ -676,11 +676,49 @@ extension String: ExpressibleByStringLiteral {
 extension String: CustomDebugStringConvertible {
  /// A representation of the string that is suitable for debugging.
  public var debugDescription: String {
+ func hasBreak(between left: String, and right: Unicode.Scalar) -> Bool {
+ // Note: we know `left` ends with an ASCII character, so we only need to
+ // look at its last scalar.
+ var state = _GraphemeBreakingState()
+ return state.shouldBreak(between: left.unicodeScalars.last!, and: right)
+ }
+
+ // Prevent unquoted scalars in the string from combining with the opening
+ // `"` or the tail of the preceding quoted scalar.
  var result = "\""
+ var wantBreak = true // true if next scalar must not combine with the last
  for us in self.unicodeScalars {
- result += us.escaped(asASCII: false)
+ if let escaped = us._escaped(asASCII: false) {
+ result += escaped
+ wantBreak = true
+ } else if wantBreak && !hasBreak(between: result, and: us) {
+ result += us.escaped(asASCII: true)
+ wantBreak = true
+ } else {
+ result.unicodeScalars.append(us)
+ wantBreak = false
+ }
+ }
+ // Also prevent the last scalar from combining with the closing `"`.
+ var suffix = "\"".unicodeScalars
+ while !result.isEmpty {
+ // Append first scalar of suffix, then check if it combines.
+ result.unicodeScalars.append(suffix.first!)
+ let i = result.index(before: result.endIndex)
+ let j = result.unicodeScalars.index(before: result.endIndex)
+ if i >= j {
+ // All good; append the rest and we're done.
+ result.unicodeScalars.append(contentsOf: suffix.dropFirst())
+ break
+ }
+ // Cancel appending the scalar, then quote the last scalar in `result` and
+ // prepend it to `suffix`.
+ result.unicodeScalars.removeLast()
+ let last = result.unicodeScalars.removeLast()
+ suffix.insert(
+ contentsOf: last.escaped(asASCII: true).unicodeScalars,
+ at: suffix.startIndex)
  }
- result += "\""
  return result
  }
 }

stdlib/public/core/UnicodeScalar.swift

@@ -192,6 +192,10 @@ extension Unicode.Scalar :
  /// ASCII characters; otherwise, pass `false`.
  /// - Returns: A string representation of the scalar.
  public func escaped(asASCII forceASCII: Bool) -> String {
+ _escaped(asASCII: forceASCII) ?? String(self)
+ }
+
+ internal func _escaped(asASCII forceASCII: Bool) -> String? {
  func lowNibbleAsHex(_ v: UInt32) -> String {
  let nibble = v & 15
  if nibble < 10 {
@@ -208,7 +212,7 @@ extension Unicode.Scalar :
  } else if self == "\"" {
  return "\\\""
  } else if _isPrintableASCII {
- return String(self)
+ return nil
  } else if self == "\0" {
  return "\\0"
  } else if self == "\n" {
@@ -222,7 +226,7 @@ extension Unicode.Scalar :
  + lowNibbleAsHex(UInt32(self) >> 4)
  + lowNibbleAsHex(UInt32(self)) + "}"
  } else if !forceASCII {
- return String(self)
+ return nil
  } else if UInt32(self) <= 0xFFFF {
  var result = "\\u{"
  result += lowNibbleAsHex(UInt32(self) >> 12)

test/stdlib/PrintString.swift

@@ -29,16 +29,60 @@ PrintTests.test("Printable") {
 
  let us1: UnicodeScalar = "\\"
  expectPrinted("\\", us1)
- expectEqual("\"\\\\\"", us1.description)
+ expectEqual("\\", us1.description)
  expectDebugPrinted("\"\\\\\"", us1)
 
  let us2: UnicodeScalar = "あ"
  expectPrinted("あ", us2)
- expectEqual("\"あ\"", us2.description)
+ expectEqual("あ", us2.description)
  expectDebugPrinted("\"\\u{3042}\"", us2)
 }
 
-PrintTests.test("Printable") {
+PrintTests.test("TrickyQuoting") {
+ guard #available(SwiftStdlib 5.9, *) else { return }
+ // U+301: COMBINING ACUTE ACCENT (Grapheme_Cluster_Break = Extend)
+ let s1 = "\u{301}Foo"
+ expectPrinted(s1, s1)
+ expectDebugPrinted("\"\\u{0301}Foo\"", s1)
+
+ // U+302: COMBINING CIRCUMFLEX ACCENT (Grapheme_Cluster_Break = Extend)
+ let s2 = "\u{301}\u{302}Foo"
+ expectPrinted(s2, s2)
+ expectDebugPrinted("\"\\u{0301}\\u{0302}Foo\"", s2)
+
+ let s3 = "Foo\n\u{301}\u{302}Foo"
+ expectPrinted(s3, s3)
+ expectDebugPrinted("\"Foo\\n\\u{0301}\\u{0302}Foo\"", s3)
+
+ // U+200D: ZERO WIDTH JOINER (Grapheme_Cluster_Break = ZWJ)
+ let s4 = "\u{200d}Foo"
+ expectPrinted(s4, s4)
+ expectDebugPrinted("\"\\u{200D}Foo\"", s4)
+
+ // U+110BD: KAITHI NUMBER SIGN (Grapheme_Cluster_Break = Prepend)
+ let s5 = "Foo\u{110BD}"
+ expectPrinted(s5, s5)
+ expectDebugPrinted("\"Foo\\u{000110BD}\"", s5)
+
+ // U+070F: SYRIAC ABBREVIATION MARK (Grapheme_Cluster_Break = Prepend)
+ let s6 = "Foo\u{070F}\u{110BD}"
+ expectPrinted(s6, s6)
+ expectDebugPrinted("\"Foo\\u{070F}\\u{000110BD}\"", s6)
+
+ let s7 = "Foo\u{301}\u{070F}\u{110BD}"
+ expectPrinted(s7, s7)
+ expectDebugPrinted("\"Foo\u{301}\\u{070F}\\u{000110BD}\"", s7)
+
+ let s8 = "Foo\u{301}\u{302}\u{070F}\u{110BD}Foo"
+ expectPrinted(s8, s8)
+ expectDebugPrinted("\"Foo\u{0301}\u{0302}\u{070F}\u{110BD}Foo\"", s8)
+
+ let s9 = "Foo\u{301}"
+ expectPrinted(s9, s9)
+ expectDebugPrinted("\"Foo\u{0301}\"", s9)
+}
+
+PrintTests.test("Optional") {
  expectPrinted("Optional(\"meow\")", String?("meow"))
 }