Escaped characters detection in literals

Sources/SnapshotTesting/AssertInlineSnapshot.swift

@@ -168,6 +168,7 @@ internal struct Context {
   let sourceCode: String
   let diffable: String
   let fileName: String
+  // First line of a file is line 1 (as with the #line macro)
   let lineIndex: Int
 
   func setSourceCode(_ newSourceCode: String) -> Context {
@@ -216,7 +217,35 @@ internal func writeInlineSnapshot(_ recordings: inout Recordings,
   }
 
   /// Find the end of multi-line literal and replace contents with recording.
-  if let multiLineLiteralEndIndex = sourceCodeLines[offsetStartIndex...].firstIndex(where: { $0.contains(multiLineStringLiteralTerminator) }) {
+  if let multiLineLiteralEndIndex = sourceCodeLines[offsetStartIndex...].firstIndex(where: { $0.hasClosingMultilineStringDelimiter() }) {
+
+    let diffableLines = context.diffable.split(separator: "\n")
+
+    // Add #'s to the multiline string literal if needed
+    let numberSigns: String
+    if context.diffable.hasEscapedSpecialCharactersLiteral() {
+      numberSigns = String(repeating: "#", count: context.diffable.numberOfNumberSignsNeeded())
+    } else if nil != diffableLines.first(where: { $0.endsInBackslash() }) {
+      // We want to avoid \ being interpreted as an escaped newline in the recorded inline snapshot
+      numberSigns = "#"
+    } else {
+      numberSigns = ""
+    }
+    let multiLineStringLiteralTerminatorPre = numberSigns + multiLineStringLiteralTerminator
+    let multiLineStringLiteralTerminatorPost = multiLineStringLiteralTerminator + numberSigns
+
+    // Update opening (#...)"""
+    sourceCodeLines[functionLineIndex].replaceFirstOccurrence(
+      of: extendedOpeningStringDelimitersPattern,
+      with: multiLineStringLiteralTerminatorPre
+    )
+
+    // Update closing """(#...)
+    sourceCodeLines[multiLineLiteralEndIndex].replaceFirstOccurrence(
+      of: extendedClosingStringDelimitersPattern,
+      with: multiLineStringLiteralTerminatorPost
+    )
+
     /// Convert actual value to Lines to insert
     let indentText = indentation(of: sourceCodeLines[multiLineLiteralEndIndex])
     let newDiffableLines = context.diffable
@@ -250,8 +279,32 @@ private func indentation<S: StringProtocol>(of str: S) -> String {
   return String(repeating: " ", count: count)
 }
 
+fileprivate extension Substring {
+  mutating func replaceFirstOccurrence(of pattern: String, with newString: String) {
+    let newString = replacingOccurrences(of: pattern, with: newString, options: .regularExpression)
+    self = Substring(newString)
+  }
+
+  func hasOpeningMultilineStringDelimiter() -> Bool {
+    return range(of: extendedOpeningStringDelimitersPattern, options: .regularExpression) != nil
+  }
+
+  func hasClosingMultilineStringDelimiter() -> Bool {
+    return range(of: extendedClosingStringDelimitersPattern, options: .regularExpression) != nil
+  }
+
+  func endsInBackslash() -> Bool {
+    if let lastChar = last {
+      return lastChar == Character(#"\"#)
+    }
+    return false
+  }
+}
+
 private let emptyStringLiteralWithCloseBrace = "\"\")"
 private let multiLineStringLiteralTerminator = "\"\"\""
+private let extendedOpeningStringDelimitersPattern = #"#{0,}\"\"\""#
+private let extendedClosingStringDelimitersPattern = ##"\"\"\"#{0,}"##
 
 // When we modify a file, the line numbers reported by the compiler through #line are no longer
 // accurate. With the FileRecording values we keep track of we modify the files so we can adjust

Sources/SnapshotTesting/Common/String+SpecialCharacters.swift

@@ -0,0 +1,57 @@
+import Foundation
+
+extension String {
+
+  /// Checks whether the string has escaped special character literals or not.
+  ///
+  /// This method won't detect an unescaped special character.
+  /// For example, this method will return true for "\\n" or #"\n"#, but false for "\n"
+  ///
+  /// The following are the special character literals that this methods looks for:
+  /// The escaped special characters \0 (null character), \\ (backslash),
+  /// \t (horizontal tab), \n (line feed), \r (carriage return),
+  /// \" (double quotation mark) and \' (single quotation mark),
+  /// An arbitrary Unicode scalar value, written as \u{n},
+  /// where n is a 1–8 digit hexadecimal number (Unicode is discussed in Unicode below)
+  /// The character sequence "#
+  ///
+  /// - Returns: True if the string has any special character literals, false otherwise.
+  func hasEscapedSpecialCharactersLiteral() -> Bool {
+    let multilineLiteralAndNumberSign = ##"""
+    """#
+    """##
+    let patterns = [
+      // Matches \u{n} where n is a 1–8 digit hexadecimal number
+      try? NSRegularExpression(pattern: #"\\u\{[a-fA-f0-9]{1,8}\}"#, options: .init()),
+      try? NSRegularExpression(pattern: #"\0"#, options: .ignoreMetacharacters),
+      try? NSRegularExpression(pattern: #"\\"#, options: .ignoreMetacharacters),
+      try? NSRegularExpression(pattern: #"\t"#, options: .ignoreMetacharacters),
+      try? NSRegularExpression(pattern: #"\n"#, options: .ignoreMetacharacters),
+      try? NSRegularExpression(pattern: #"\r"#, options: .ignoreMetacharacters),
+      try? NSRegularExpression(pattern: #"\""#, options: .ignoreMetacharacters),
+      try? NSRegularExpression(pattern: #"\'"#, options: .ignoreMetacharacters),
+      try? NSRegularExpression(pattern: multilineLiteralAndNumberSign, options: .ignoreMetacharacters),
+    ]
+    let matches = patterns.compactMap { $0?.firstMatch(in: self, options: .init(), range: NSRange.init(location: 0, length: self.count)) }
+    return matches.count > 0
+  }
+
+
+  /// This method calculates how many number signs (#) we need to add around a string
+  /// literal to properly escape its content.
+  ///
+  /// Multiple # are needed when the literal contains "#, "##, "### ...
+  ///
+  /// - Returns: The number of "number signs(#)" needed around a string literal.
+  ///            When there is no "#, ... return 1
+  func numberOfNumberSignsNeeded() -> Int {
+    let pattern = try! NSRegularExpression(pattern: ##""#{1,}"##, options: .init())
+
+    let matches = pattern.matches(in: self, options: .init(), range: NSRange.init(location: 0, length: self.count))
+
+    // If we have "## then the length of the match is 3,
+    // which is also the number of "number signs (#)" we need to add
+    // before and after the string literal
+    return matches.map { $0.range.length }.max() ?? 1
+  }
+}