Fix an infinite loop if a conflict marker is found but it's not at the start of a new line

rdar://137746823

Author: ahoppen

Sources/SwiftParser/Lexer/Cursor.swift

@@ -2448,6 +2448,7 @@ extension Lexer.Cursor {
 
       // Must occur at start of line.
       guard restOfBuffer.previous == "\n" || restOfBuffer.previous == "\r" else {
+        _ = restOfBuffer.advance()
         continue
       }
 

Tests/SwiftParserTest/LexerTests.swift

@@ -1706,4 +1706,19 @@ class LexerTests: ParserTestCase {
       ]
     )
   }
+
+  func testConflictMarkerNotAtStartOfLine() {
+    assertLexemes(
+      #"""
+      <<<<<<< a
+       >>>>>>> a
+      """#,
+      lexemes: [
+        LexemeSpec(.binaryOperator, text: "<<<<<<<", trailing: " "),
+        LexemeSpec(.identifier, text: "a"),
+        LexemeSpec(.binaryOperator, leading: "\n ", text: ">>>>>>>", trailing: " ", flags: [.isAtStartOfLine]),
+        LexemeSpec(.identifier, text: "a"),
+      ]
+    )
+  }
 }