MDEV-20797 FULLTEXT search with apostrophe, and mandatory words

- InnoDB should ignore the single word followed by apostrophe while
tokenising the document. Example is that if the input string is O'brien
then right now, InnoDB seperates into two tokens as O, brien. But
after this patch, InnoDB can ignore the token 'O' and consider
only 'brien'.

mysql-test/suite/innodb_fts/r/fulltext.result

@@ -732,4 +732,32 @@ ALTER TABLE t1 DROP KEY `ftidx` ;
 INSERT INTO t1 (col_int, col_text) VALUES ( 1255, NULL);
 DROP TABLE t1;
 SET @@global.innodb_file_per_table = @save;
+#
+# MDEV-20797  FULLTEXT search with apostrophe,
+#		and mandatory words
+#
+CREATE TABLE t1(f1 TINYTEXT NOT NULL, FULLTEXT(f1))ENGINE=InnoDB;
+INSERT INTO t1 VALUES('O''Brien'), ('O Brien'), ('''Brien');
+INSERT INTO t1 VALUES('Brien'), ('O ''Brien'), ('O'' Brien');
+INSERT INTO t1 VALUES('Doh''nuts');
+SELECT * FROM t1 WHERE MATCH (f1) AGAINST ("+O'Brien" IN BOOLEAN MODE);
+f1
+O'Brien
+O Brien
+'Brien
+Brien
+O 'Brien
+O' Brien
+SELECT * FROM t1 WHERE MATCH (f1) AGAINST ("+Doh'nuts" IN BOOLEAN MODE);
+f1
+Doh'nuts
+SELECT * FROM t1 WHERE MATCH (f1) AGAINST ("+''Brien" IN BOOLEAN MODE);
+f1
+O'Brien
+O Brien
+'Brien
+Brien
+O 'Brien
+O' Brien
+DROP TABLE t1;
 # End of 10.3 tests

mysql-test/suite/innodb_fts/t/fulltext.test

@@ -757,4 +757,17 @@ INSERT INTO t1 (col_int, col_text) VALUES ( 1255, NULL);
 DROP TABLE t1;
 SET @@global.innodb_file_per_table = @save;
 
+--echo #
+--echo # MDEV-20797  FULLTEXT search with apostrophe,
+--echo #		and mandatory words
+--echo #
+CREATE TABLE t1(f1 TINYTEXT NOT NULL, FULLTEXT(f1))ENGINE=InnoDB;
+INSERT INTO t1 VALUES('O''Brien'), ('O Brien'), ('''Brien');
+INSERT INTO t1 VALUES('Brien'), ('O ''Brien'), ('O'' Brien');
+INSERT INTO t1 VALUES('Doh''nuts');
+SELECT * FROM t1 WHERE MATCH (f1) AGAINST ("+O'Brien" IN BOOLEAN MODE);
+SELECT * FROM t1 WHERE MATCH (f1) AGAINST ("+Doh'nuts" IN BOOLEAN MODE);
+SELECT * FROM t1 WHERE MATCH (f1) AGAINST ("+''Brien" IN BOOLEAN MODE);
+DROP TABLE t1;
+
 --echo # End of 10.3 tests

storage/innobase/handler/ha_innodb.cc

@@ -6912,7 +6912,8 @@ innobase_mysql_fts_get_token(
 
 	ulint	mwc = 0;
 	ulint	length = 0;
-
+	bool	reset_token_str = false;
+reset:
 	token->f_str = const_cast<byte*>(doc);
 
 	while (doc < end) {
@@ -6923,6 +6924,9 @@ innobase_mysql_fts_get_token(
 			cs, &ctype, (uchar*) doc, (uchar*) end);
 		if (true_word_char(ctype, *doc)) {
 			mwc = 0;
+		} else if (*doc == '\'' && length == 1) {
+			/* Could be apostrophe */
+			reset_token_str = true;
 		} else if (!misc_word_char(*doc) || mwc) {
 			break;
 		} else {
@@ -6932,6 +6936,14 @@ innobase_mysql_fts_get_token(
 		++length;
 
 		doc += mbl > 0 ? mbl : (mbl < 0 ? -mbl : 1);
+		if (reset_token_str) {
+			/* Reset the token if the single character
+			followed by apostrophe */
+			mwc = 0;
+			length = 0;
+			reset_token_str = false;
+			goto reset;
+		}
 	}
 
 	token->f_len = (uint) (doc - token->f_str) - mwc;