From 994695c669085058c4a500f295a0531893eff77a Mon Sep 17 00:00:00 2001
From: Marcel Greter <marcel.greter@ocbnet.ch>
Date: Sun, 3 Nov 2019 00:42:10 +0100
Subject: [PATCH] Fix out of boundary vector access

Fixes https://github.com/sass/libsass/issues/3001
---
 src/parser_selectors.cpp | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/src/parser_selectors.cpp b/src/parser_selectors.cpp
index d76dd2ca7..3b4a6e2d9 100644
--- a/src/parser_selectors.cpp
+++ b/src/parser_selectors.cpp
@@ -140,10 +140,12 @@ namespace Sass {
         // parent selector only allowed at start
         // upcoming Sass may allow also trailing
         ParserState state(pstate);
-        SimpleSelectorObj prev = (*seq)[seq->length()-1];
-        std::string sel(prev->to_string({ NESTED, 5 }));
         std::string found("&");
-        if (lex < identifier >()) { found += std::string(lexed); }
+        if (lex < identifier >()) {
+          found += std::string(lexed);
+        }
+        std::string sel(seq->hasRealParent() ? "&" : "");
+        if (!seq->empty()) { sel = seq->last()->to_string({ NESTED, 5 }); }
         // ToDo: parser should throw parser exceptions
         error("Invalid CSS after \"" + sel + "\": expected \"{\", was \"" + found + "\"\n\n"
           "\"" + found + "\" may only be used at the beginning of a compound selector.", state);