Merge pull request #1553 from cbjeukendrup/prefer_first_lex_err_in_string_literal

Prefer the first lexical error in a string literal segment

Author: ahoppen

Sources/SwiftParser/Lexer/Cursor.swift

@@ -1913,7 +1913,10 @@ extension Lexer.Cursor {
           return Lexer.Result(.stringSegment, error: error)
         }
       case .error(let errorKind):
-        error = LexingDiagnostic(errorKind, position: self)
+        // Only overwrite error if we had not found an earlier error yet
+        if error == nil {
+          error = LexingDiagnostic(errorKind, position: self)
+        }
         self = clone
       case .endOfString:
         return Lexer.Result(

Tests/SwiftParserTest/ExpressionTests.swift

@@ -611,6 +611,13 @@ final class ExpressionTests: XCTestCase {
         DiagnosticSpec(locationMarker: "2️⃣", message: #"expected '"' to end string literal"#, fixIts: [#"insert '"'"#]),
       ]
     )
+
+    assertParse(
+      ###""1️⃣\1 \1""###,
+      diagnostics: [
+        DiagnosticSpec(message: "invalid escape sequence in literal")
+      ]
+    )
   }
 
   func testAdjacentRawStringLiterals() {