Make sure we convert the source to a native UTF-8 string before parsing

Sources/SwiftSyntax/SyntaxParser.swift

@@ -89,7 +89,7 @@ public enum SyntaxParser {
     // If the string is backed by an NSString then such indexing will become
     // extremely slow.
     var utf8Source = source
-    utf8Source.makeNativeUTF8IfNeeded()
+    utf8Source.makeContiguousUTF8()
 
     let rawSyntax = parseRaw(utf8Source, parseTransition, filenameForDiagnostics,
                              diagnosticEngine)
@@ -127,7 +127,7 @@ public enum SyntaxParser {
     _ filenameForDiagnostics: String,
     _ diagnosticEngine: DiagnosticEngine?
   ) -> RawSyntax {
-    assert(source.isNativeUTF8)
+    precondition(source.isContiguousUTF8)
     let c_parser = swiftparse_parser_create()
     defer {
       swiftparse_parser_dispose(c_parser)

Sources/SwiftSyntax/TokenKind.swift.gyb

@@ -172,7 +172,7 @@ extension TokenKind {
       return body(.init(kind: .${token.swift_kind()}, length: length))
 %   else:
     case .${token.swift_kind()}(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .${token.swift_kind()}, length: length, customText: buf))

Sources/SwiftSyntax/Trivia.swift.gyb

@@ -236,7 +236,7 @@ extension TriviaPiece {
       return body(.init(kind: .${trivia.lower_name}s, length: length))
 %   else:
     case var .${trivia.lower_name}(text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .${trivia.lower_name}, length: length, customText: buf))

Sources/SwiftSyntax/Utils.swift

@@ -73,26 +73,6 @@ extension String {
   static func fromBuffer(_ textBuffer: UnsafeBufferPointer<UInt8>) -> String {
     return String(decoding: textBuffer, as: UTF8.self)
   }
-
-  var isNativeUTF8: Bool {
-    return utf8.withContiguousStorageIfAvailable { _ in 0 } != nil
-  }
-
-  mutating func makeNativeUTF8IfNeeded() {
-    if !isNativeUTF8 {
-      self += ""
-    }
-  }
-
-  func utf8Slice(offset: Int, length: Int) -> Substring {
-    if length == 0 {
-      return Substring()
-    }
-    let utf8 = self.utf8
-    let begin = utf8.index(utf8.startIndex, offsetBy: offset)
-    let end = utf8.index(begin, offsetBy: length)
-    return Substring(utf8[begin..<end])
-  }
 }
 
 extension UnsafeBufferPointer where Element == UInt8 {

Sources/SwiftSyntax/gyb_generated/TokenKind.swift

@@ -1771,79 +1771,79 @@ extension TokenKind {
       let length = 13
       return body(.init(kind: .poundColorLiteralKeyword, length: length))
     case .integerLiteral(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .integerLiteral, length: length, customText: buf))
       })!
     case .floatingLiteral(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .floatingLiteral, length: length, customText: buf))
       })!
     case .stringLiteral(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .stringLiteral, length: length, customText: buf))
       })!
     case .unknown(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .unknown, length: length, customText: buf))
       })!
     case .identifier(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .identifier, length: length, customText: buf))
       })!
     case .unspacedBinaryOperator(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .unspacedBinaryOperator, length: length, customText: buf))
       })!
     case .spacedBinaryOperator(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .spacedBinaryOperator, length: length, customText: buf))
       })!
     case .postfixOperator(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .postfixOperator, length: length, customText: buf))
       })!
     case .prefixOperator(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .prefixOperator, length: length, customText: buf))
       })!
     case .dollarIdentifier(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .dollarIdentifier, length: length, customText: buf))
       })!
     case .contextualKeyword(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .contextualKeyword, length: length, customText: buf))
       })!
     case .rawStringDelimiter(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .rawStringDelimiter, length: length, customText: buf))
       })!
     case .stringSegment(var text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .stringSegment, length: length, customText: buf))

Sources/SwiftSyntax/gyb_generated/Trivia.swift

@@ -366,31 +366,31 @@ extension TriviaPiece {
       let length = count * 2
       return body(.init(kind: .carriageReturnLineFeeds, length: length))
     case var .lineComment(text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .lineComment, length: length, customText: buf))
       })!
     case var .blockComment(text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .blockComment, length: length, customText: buf))
       })!
     case var .docLineComment(text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .docLineComment, length: length, customText: buf))
       })!
     case var .docBlockComment(text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .docBlockComment, length: length, customText: buf))
       })!
     case var .garbageText(text):
-      text.makeNativeUTF8IfNeeded()
+      text.makeContiguousUTF8()
       let length = text.utf8.count
       return text.utf8.withContiguousStorageIfAvailable({ (buf: UnsafeBufferPointer<UInt8>) in
         return body(.init(kind: .garbageText, length: length, customText: buf))

Tests/SwiftSyntaxTest/SyntaxTests.swift

@@ -144,4 +144,11 @@ public class SyntaxTests: XCTestCase {
     XCTAssertEqual(Syntax(integerExpr), Syntax(fromProtocol: integerExpr as SyntaxProtocol))
     XCTAssertEqual(Syntax(integerExpr), Syntax(fromProtocol: integerExpr as ExprSyntaxProtocol))
   }
+
+  public func testRunParserOnForeignString() {
+    // Store the source code in a foreign non-UTF-8 string.
+    // If SwiftSyntax fails to convert it to a native UTF-8 string, internal assertions should fail.
+    let sourceNsString = "var 🎉 = 2" as NSString
+    _ = try? SyntaxParser.parse(source: sourceNsString as String)
+  }
 }