Keep line breaks quoted when serializing CSV fields

SwiftCSV/Serializer.swift

@@ -37,9 +37,9 @@ fileprivate extension String {
     static let quote = "\""
 
     func enquoted(whenContaining separator: String) -> String {
-        // If value contains a delimiter or quotes, double any embedded quotes and surround with quotes.
+        // Quote fields containing delimiters, quotes or line breaks, and double embedded quotes.
         // For more information, see https://www.rfc-editor.org/rfc/rfc4180.html
-        if self.contains(separator) || self.contains(Self.quote) {
+        if self.contains(separator) || self.contains(Self.quote) || self.contains(where: { $0.isNewline }) {
             return Self.quote + self.replacingOccurrences(of: Self.quote, with: Self.quote + Self.quote) + Self.quote
         } else {
             return self

SwiftCSVTests/SerializationNewlineTests.swift

@@ -0,0 +1,28 @@
+import XCTest
+@testable import SwiftCSV
+
+class SerializationNewlineTests: XCTestCase {
+    func testLineBreaksRemainQuotedForEnumeratedRoundTrip() throws {
+        for newline in ["\n", "\r", "\r\n"] {
+            for delimiter: CSVDelimiter in [.comma, .semicolon, .tab, .character("|")] {
+                let separator = String(delimiter.rawValue)
+                let source = "\"first\(newline)name\"\(separator)second\n\"value\(newline)continued\"\(separator)other"
+                let original = try EnumeratedCSV(string: source, delimiter: delimiter)
+                XCTAssertEqual(original.serialized, source)
+                let decoded = try EnumeratedCSV(string: original.serialized, delimiter: delimiter)
+                XCTAssertEqual(decoded.header, original.header)
+                XCTAssertEqual(decoded.rows, original.rows)
+            }
+        }
+    }
+
+    func testLineBreaksRemainQuotedForNamedRoundTrip() throws {
+        for newline in ["\n", "\r", "\r\n"] {
+            let source = "name,note\nAlice,\"first\(newline)second\""
+            let original = try NamedCSV(string: source, delimiter: .comma)
+            XCTAssertEqual(original.serialized, source)
+            let decoded = try NamedCSV(string: original.serialized, delimiter: .comma)
+            XCTAssertEqual(decoded.rows, original.rows)
+        }
+    }
+}