From 08ea68dc1f3ffc387796addaacaeb40e4e566763 Mon Sep 17 00:00:00 2001
From: Maxime Coste <mawww@kakoune.org>
Date: Sun, 8 Oct 2017 11:16:03 +0800
Subject: [PATCH] Regex: Fix handling of match_prev_avail for boost regex

We were passing around iterators that were not allowed to
go before the begin iterator.
---
 src/regex.hh | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/regex.hh b/src/regex.hh
index 3d067b0b..eecb947d 100644
--- a/src/regex.hh
+++ b/src/regex.hh
@@ -180,7 +180,8 @@ bool regex_search(It begin, It end, const Regex& re,
 {
     try
     {
-        bool matched = boost::regex_search<RegexUtf8It<It>>({begin, begin, end}, {end, begin, end}, re, flags);
+        auto first = (flags & RegexConstant::match_prev_avail) ? begin-1 : begin;
+        bool matched = boost::regex_search<RegexUtf8It<It>>({begin, first, end}, {end, first, end}, re, flags);
         if (re.impl() and matched != regex_search(begin, end, *re.impl(), convert_flags(flags)))
             regex_mismatch(re);
         return matched;
@@ -197,7 +198,8 @@ bool regex_search(It begin, It end, MatchResults<It>& res, const Regex& re,
 {
     try
     {
-        bool matched = boost::regex_search<RegexUtf8It<It>>({begin, begin, end}, {end, begin, end}, res, re, flags);
+        auto first = (flags & RegexConstant::match_prev_avail) ? begin-1 : begin;
+        bool matched = boost::regex_search<RegexUtf8It<It>>({begin, first, end}, {end, first, end}, res, re, flags);
         Vector<It> captures;
         if (re.impl() and matched != regex_search(begin, end, captures, *re.impl(), convert_flags(flags)))
             regex_mismatch(re);