Allow empty replacement strings in contrib/unaccent.

This is useful in languages where diacritic signs are represented as
separate characters; it's also one step towards letting unaccent be used
for arbitrary substring substitutions.

In passing, improve the user documentation for unaccent, which was sadly
vague about some important details.

Mohammad Alhashash, reviewed by Abhijit Menon-Sen

1 files changed, 23 insertions, 6 deletions

diff --git a/contrib/unaccent/unaccent.c b/contrib/unaccent/unaccent.c
index a337df61af4..5a31f85a132 100644
--- a/contrib/unaccent/unaccent.c
+++ b/contrib/unaccent/unaccent.c
@@ -104,11 +104,21 @@ initTrie(char *filename)
 
 			while ((line = tsearch_readline(&trst)) != NULL)
 			{
-				/*
-				 * The format of each line must be "src trg" where src and trg
-				 * are sequences of one or more non-whitespace characters,
-				 * separated by whitespace.  Whitespace at start or end of
-				 * line is ignored.
+				/*----------
+				 * The format of each line must be "src" or "src trg", where
+				 * src and trg are sequences of one or more non-whitespace
+				 * characters, separated by whitespace.  Whitespace at start
+				 * or end of line is ignored.  If trg is omitted, an empty
+				 * string is used as the replacement.
+				 *
+				 * We use a simple state machine, with states
+				 *	0	initial (before src)
+				 *	1	in src
+				 *	2	in whitespace after src
+				 *	3	in trg
+				 *	4	in whitespace after trg
+				 *	-1	syntax error detected (line will be ignored)
+				 *----------
 				 */
 				int			state;
 				char	   *ptr;
@@ -160,7 +170,14 @@ initTrie(char *filename)
 					}
 				}
 
-				if (state >= 3)
+				if (state == 1 || state == 2)
+				{
+					/* trg was omitted, so use "" */
+					trg = "";
+					trglen = 0;
+				}
+
+				if (state > 0)
 					rootTrie = placeChar(rootTrie,
 										 (unsigned char *) src, srclen,
 										 trg, trglen);