From 304dcb656eded40707499c2194b5da3841012c7c Mon Sep 17 00:00:00 2001
From: Steven Watanabe <steven@providere-consulting.com>
Date: Wed, 3 Apr 2019 11:28:54 -0600
Subject: [PATCH] Handle empty matches in regex.replace.  Fixes #421.

---
 src/engine/modules/regex.c | 8 +++++++-
 src/util/regex.jam         | 1 +
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/engine/modules/regex.c b/src/engine/modules/regex.c
index d9f8177bf..281e23ad7 100644
--- a/src/engine/modules/regex.c
+++ b/src/engine/modules/regex.c
@@ -108,7 +108,13 @@ LIST * regex_replace( FRAME * frame, int flags )
     {
         string_append_range( buf, pos, re->startp[ 0 ] );
         string_append( buf, object_str( replacement ) );
-        pos = re->endp[ 0 ];
+        /* Handle empty matches */
+        if ( *pos == '\0' )
+            break;
+        else if ( pos == re->endp[ 0 ] )
+            ++pos;
+        else
+            pos = re->endp[ 0 ];
     }
     string_append( buf, pos );
 
diff --git a/src/util/regex.jam b/src/util/regex.jam
index 766a231a6..483c6220e 100644
--- a/src/util/regex.jam
+++ b/src/util/regex.jam
@@ -198,6 +198,7 @@ rule __test__ ( )
     assert.result "&nbsp;string&nbsp;string" : replace " string string" " " "&nbsp;" ;
     assert.result "string&nbsp;&nbsp;string" : replace "string  string" " " "&nbsp;" ;
     assert.result "-" : replace "&" "&" "-" ;
+    assert.result "x" : replace "" "" "x" ;
 
     assert.result "-" "a-b" : replace-list "&" "a&b" : "&" : "-" ;
 }