From f7c66eadce38b582ba00462f72776fbeefa1c0d3 Mon Sep 17 00:00:00 2001
From: Casper Jeukendrup <48658420+cbjeukendrup@users.noreply.github.com>
Date: Sat, 15 Apr 2023 19:20:56 +0200
Subject: [PATCH] Prefer the first lexical error in a string literal segment

Resolves: #1480
---
 Sources/SwiftParser/Lexer/Cursor.swift      | 5 ++++-
 Tests/SwiftParserTest/ExpressionTests.swift | 7 +++++++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/Sources/SwiftParser/Lexer/Cursor.swift b/Sources/SwiftParser/Lexer/Cursor.swift
index 6497ac19456..40a645af84d 100644
--- a/Sources/SwiftParser/Lexer/Cursor.swift
+++ b/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(
diff --git a/Tests/SwiftParserTest/ExpressionTests.swift b/Tests/SwiftParserTest/ExpressionTests.swift
index 17c6fbf026e..007bcc55f8a 100644
--- a/Tests/SwiftParserTest/ExpressionTests.swift
+++ b/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() {