Fix regexp_matches() handling of zero-length matches.

We'd find the same match twice if it was of zero length and not immediately
adjacent to the previous match.  replace_text_regexp() got similar cases
right, so adjust this search logic to match that.  Note that even though
the regexp_split_to_xxx() functions share this code, they did not display
equivalent misbehavior, because the second match would be considered
degenerate and ignored.

Jeevan Chalke, with some cosmetic changes by me.

1 files changed, 6 insertions, 7 deletions

diff --git a/src/backend/utils/adt/regexp.c b/src/backend/utils/adt/regexp.c
index 67e205d0816..b15b0905b74 100644
--- a/src/backend/utils/adt/regexp.c
+++ b/src/backend/utils/adt/regexp.c
@@ -957,14 +957,13 @@ setup_regexp_matches(text *orig_str, text *pattern, text *flags,
 			break;
 
 		/*
-		 * Advance search position.  Normally we start just after the end of
-		 * the previous match, but always advance at least one character (the
-		 * special case can occur if the pattern matches zero characters just
-		 * after the prior match or at the end of the string).
+		 * Advance search position.  Normally we start the next search at the
+		 * end of the previous match; but if the match was of zero length, we
+		 * have to advance by one character, or we'd just find the same match
+		 * again.
 		 */
-		if (start_search < pmatch[0].rm_eo)
-			start_search = pmatch[0].rm_eo;
-		else
+		start_search = prev_match_end;
+		if (pmatch[0].rm_so == pmatch[0].rm_eo)
 			start_search++;
 		if (start_search > wide_len)
 			break;