Add support for minimum field width for strings to my_vsnprintf()

This patch adds support for right aligned strings and numbers.
Left alignment is left as an exercise for anyone needing it.

MDEV-25612 "Assertion `to <= end' failed in process_args" fixed.
(Was caused by the original version of this patch)

mysql-test/main/almost_full.result

@@ -7,24 +7,24 @@ INSERT INTO t1 SET b=repeat('a',600);
 ERROR HY000: The table 't1' is full
 CHECK TABLE t1 EXTENDED;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 65448 of 65534 used
+test.t1	check	warning	Datafile is almost full,      65448 of      65534 used
 test.t1	check	status	OK
 UPDATE t1 SET b=repeat('a', 800) where a=10;
 ERROR HY000: The table 't1' is full
 CHECK TABLE t1 EXTENDED;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 65448 of 65534 used
+test.t1	check	warning	Datafile is almost full,      65448 of      65534 used
 test.t1	check	status	OK
 INSERT INTO t1 SET b=repeat('a',400);
 CHECK TABLE t1 EXTENDED;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 65448 of 65534 used
+test.t1	check	warning	Datafile is almost full,      65448 of      65534 used
 test.t1	check	status	OK
 DELETE FROM t1 WHERE a=2 or a=6;
 UPDATE t1 SET b=repeat('a', 600) where a=11;
 CHECK TABLE t1 EXTENDED;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 65448 of 65534 used
+test.t1	check	warning	Datafile is almost full,      65448 of      65534 used
 test.t1	check	status	OK
 drop table t1;
 set global myisam_data_pointer_size=default;

mysql-test/main/grant4.result

@@ -187,8 +187,8 @@ connection con1;
 check table mysqltest_db1.t1;
 Table	Op	Msg_type	Msg_text
 mysqltest_db1.t1	check	warning	1 client is using or hasn't closed the table properly
-mysqltest_db1.t1	check	error	Size of indexfile is: 1024        Should be: 2048
-mysqltest_db1.t1	check	warning	Size of datafile is: 14       Should be: 7
+mysqltest_db1.t1	check	error	Size of indexfile is:     1024        Should be: 2048
+mysqltest_db1.t1	check	warning	Size of datafile is:        14       Should be: 7
 mysqltest_db1.t1	check	error	Corrupt
 # The below statement should fail before repairing t1.
 # Otherwise info about such repair will be missing from its result-set.
@@ -201,8 +201,8 @@ check table mysqltest_db1.t1;
 Table	Op	Msg_type	Msg_text
 mysqltest_db1.t1	check	warning	Table is marked as crashed
 mysqltest_db1.t1	check	warning	1 client is using or hasn't closed the table properly
-mysqltest_db1.t1	check	error	Size of indexfile is: 1024        Should be: 2048
-mysqltest_db1.t1	check	warning	Size of datafile is: 14       Should be: 7
+mysqltest_db1.t1	check	error	Size of indexfile is:     1024        Should be: 2048
+mysqltest_db1.t1	check	warning	Size of datafile is:        14       Should be: 7
 mysqltest_db1.t1	check	error	Corrupt
 repair table mysqltest_db1.t1;
 Table	Op	Msg_type	Msg_text

mysql-test/main/myisam.result

@@ -2644,8 +2644,8 @@ FLUSH TABLES;
 CHECK TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	check	warning	1 client is using or hasn't closed the table properly
-test.t1	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1	check	warning	Size of datafile is: 14       Should be: 7
+test.t1	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1	check	warning	Size of datafile is:        14       Should be: 7
 test.t1	check	error	Corrupt
 # Alter table should report error and not auto-repair the table.
 ALTER TABLE t1 ENGINE = MyISAM;
@@ -2654,8 +2654,8 @@ CHECK TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	check	warning	Table is marked as crashed
 test.t1	check	warning	1 client is using or hasn't closed the table properly
-test.t1	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1	check	warning	Size of datafile is: 14       Should be: 7
+test.t1	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1	check	warning	Size of datafile is:        14       Should be: 7
 test.t1	check	error	Corrupt
 DROP TABLE t1;
 #

mysql-test/main/myisam_crash_before_flush_keys.result

@@ -25,6 +25,6 @@ ERROR HY000: Lost connection to server during query
 CHECK TABLE t1;
 Table	Op	Msg_type	Msg_text
 test.t1	check	warning	1 client is using or hasn't closed the table properly
-test.t1	check	error	Size of indexfile is: 1024        Should be: 3072
+test.t1	check	error	Size of indexfile is:     1024        Should be: 3072
 test.t1	check	error	Corrupt
 DROP TABLE t1;

mysql-test/main/myisam_recover.result

@@ -69,9 +69,9 @@ flush table t1;
 # check table is needed to mark the table as crashed.
 check table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Size of datafile is: 42       Should be: 21
-test.t1	check	error	Record-count is not ok; is 6   Should be: 3
-test.t1	check	warning	Found 6 key parts. Should be: 3
+test.t1	check	warning	Size of datafile is:        42       Should be: 21
+test.t1	check	error	Record-count is not ok; is          6   Should be: 3
+test.t1	check	warning	Found          6 key parts. Should be: 3
 test.t1	check	error	Corrupt
 #
 # At this point we have a merge table t1_mrg pointing to t1,
@@ -122,9 +122,9 @@ flush table t1;
 # Check table is needed to mark the table as crashed.
 check table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Size of datafile is: 14       Should be: 7
-test.t1	check	error	Record-count is not ok; is 2   Should be: 1
-test.t1	check	warning	Found 2 key parts. Should be: 1
+test.t1	check	warning	Size of datafile is:        14       Should be: 7
+test.t1	check	error	Record-count is not ok; is          2   Should be: 1
+test.t1	check	warning	Found          2 key parts. Should be: 1
 test.t1	check	error	Corrupt
 # At this point we have a corrupt t1
 set autocommit = 0;

mysql-test/main/mysqlcheck.result

@@ -429,7 +429,7 @@ create table mysqltest1.t1 (a int) engine=myisam;
 create table t2 (a int);
 check table mysqltest1.t1;
 Table	Op	Msg_type	Msg_text
-mysqltest1.t1	check	warning	Size of datafile is: 4       Should be: 0
+mysqltest1.t1	check	warning	Size of datafile is:         4       Should be: 0
 mysqltest1.t1	check	error	got error: 0 when reading datafile at record: 0
 mysqltest1.t1	check	error	Corrupt
 mtr.global_suppressions                            Table is already up to date
@@ -464,7 +464,7 @@ mysql.time_zone_transition_type                    Table is already up to date
 mysql.transaction_registry                         OK
 mysqltest1.t1
 warning  : Table is marked as crashed
-warning  : Size of datafile is: 4       Should be: 0
+warning  : Size of datafile is:         4       Should be: 0
 error    : got error: 0 when reading datafile at record: 0
 error    : Corrupt
 sys.sys_config                                     Table is already up to date

mysql-test/main/strings.result

+#
+# MDEV-25612 Assertion `to <= end' failed in process_args
+#
+SET SESSION default_master_connection=REPEAT('a',190),lc_messages=ru_ru;
+CHANGE MASTER TO master_host='dummy';
+START SLAVE sql_thread;
+CHANGE MASTER TO master_user='user',master_password='pwd';
+ERROR HY000: \042D\0442\0443 \043E\043F\0435\0440\0430\0446\0438\044E \043D\0435\0432\043E\0437\043C\043E\0436\043D\043E \0432\044B\043F\043E\043B\043D\0438\0442\044C \043F\0440\0438 \0440\0430\0431\043E\0442\0430\044E\0449\0435\043C \043F\043E\0442\043E\043A\0435 \043F\043E\0434\0447\0438\043D\0435\043D\043D\043E\0433\043E \0441\0435\0440\0432\0435\0440\0430 aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
+STOP SLAVE;

mysql-test/main/strings.test

+--source include/not_windows.inc
+--source include/not_embedded.inc
+
+#
+# Test that exposes problems in string functions like my_vsnprintf
+#
+
+--echo #
+--echo # MDEV-25612 Assertion `to <= end' failed in process_args
+--echo #
+SET SESSION default_master_connection=REPEAT('a',190),lc_messages=ru_ru;
+CHANGE MASTER TO master_host='dummy';
+START SLAVE sql_thread;
+--error ER_SLAVE_MUST_STOP
+CHANGE MASTER TO master_user='user',master_password='pwd';
+STOP SLAVE;

mysql-test/suite/maria/maria-recovery3.result

@@ -100,7 +100,7 @@ ERROR HY000: Lost connection to server during query
 * recovery happens
 check table t1 extended;
 Table	Op	Msg_type	Msg_text
-mysqltest.t1	check	warning	Size of indexfile is: <SIZE>       Expected: 8192
+mysqltest.t1	check	warning	Size of indexfile is:      <SIZE>       Expected: 8192
 mysqltest.t1	check	status	OK
 * testing that checksum after recovery is as expected
 Checksum-check

mysql-test/suite/maria/max_length.result

@@ -54,20 +54,20 @@ insert into t1 (v,b) select v,b from t2;
 ERROR HY000: The table 't1' is full
 check table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 268230656 of 268320768 used
+test.t1	check	warning	Datafile is almost full,  268230656 of  268320768 used
 test.t1	check	status	OK
 insert into t1 values(null, repeat("gh",400),repeat("jkl",10000));
 ERROR HY000: The table 't1' is full
 check table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 268230656 of 268320768 used
+test.t1	check	warning	Datafile is almost full,  268230656 of  268320768 used
 test.t1	check	status	OK
 truncate table t1;
 insert into t1 (v,b) select v,b from t2;
 ERROR HY000: The table 't1' is full
 check table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 268230656 of 268320768 used
+test.t1	check	warning	Datafile is almost full,  268230656 of  268320768 used
 test.t1	check	status	OK
 drop table t1,t2;
 create table t1 (
@@ -135,7 +135,7 @@ count(*)
 3276
 check table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 65520 of 65535 used
+test.t1	check	warning	Datafile is almost full,      65520 of      65535 used
 test.t1	check	status	OK
 create or replace table t1 (
 c1 int unsigned,
@@ -172,7 +172,7 @@ count(*)
 6189940
 check table t1;
 Table	Op	Msg_type	Msg_text
-test.t1	check	warning	Datafile is almost full, 268320768 of 268320768 used
+test.t1	check	warning	Datafile is almost full,  268320768 of  268320768 used
 test.t1	check	status	OK
 show table status like "t1";
 Name	Engine	Version	Row_format	Rows	Avg_row_length	Data_length	Max_data_length	Index_length	Data_free	Auto_increment	Create_time	Update_time	Check_time	Collation	Checksum	Create_options	Comment	Max_index_length	Temporary

mysql-test/suite/parts/r/partition_recover_myisam.result

@@ -19,8 +19,8 @@ a
 Warnings:
 Error	145	Table 't1_will_crash' is marked as crashed and should be repaired
 Warning	1034	1 client is using or hasn't closed the table properly
-Error	1034	Size of indexfile is: 1024        Should be: 2048
-Warning	1034	Size of datafile is: 77       Should be: 7
+Error	1034	Size of indexfile is:     1024        Should be: 2048
+Warning	1034	Size of datafile is:        77       Should be: 7
 Warning	1034	Number of rows changed from 1 to 11
 DROP TABLE t1_will_crash;
 CREATE TABLE t1_will_crash (a INT, KEY (a))
@@ -48,7 +48,7 @@ a
 Warnings:
 Error	145	Table 't1_will_crash#P#p1' is marked as crashed and should be repaired
 Warning	1034	1 client is using or hasn't closed the table properly
-Error	1034	Size of indexfile is: 1024        Should be: 2048
-Warning	1034	Size of datafile is: 28       Should be: 7
+Error	1034	Size of indexfile is:     1024        Should be: 2048
+Warning	1034	Size of datafile is:        28       Should be: 7
 Warning	1034	Number of rows changed from 1 to 4
 DROP TABLE t1_will_crash;

mysql-test/suite/parts/r/partition_repair_myisam.result

@@ -16,8 +16,8 @@ FLUSH TABLES;
 CHECK TABLE tp;
 Table	Op	Msg_type	Msg_text
 test.tp	check	warning	1 client is using or hasn't closed the table properly
-test.tp	check	error	Size of indexfile is: 1024        Should be: 2048
-test.tp	check	warning	Size of datafile is: 77       Should be: 7
+test.tp	check	error	Size of indexfile is:     1024        Should be: 2048
+test.tp	check	warning	Size of datafile is:        77       Should be: 7
 test.tp	check	error	Partition pCrashed returned error
 test.tp	check	error	Corrupt
 ALTER TABLE tp EXCHANGE PARTITION pCrashed WITH TABLE t;
@@ -40,8 +40,8 @@ FLUSH TABLES;
 CHECK TABLE t;
 Table	Op	Msg_type	Msg_text
 test.t	check	warning	1 client is using or hasn't closed the table properly
-test.t	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t	check	warning	Size of datafile is: 77       Should be: 7
+test.t	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t	check	warning	Size of datafile is:        77       Should be: 7
 test.t	check	error	Corrupt
 ALTER TABLE tp EXCHANGE PARTITION pCrashed WITH TABLE t;
 ERROR HY000: Table './test/t' is marked as crashed and should be repaired
@@ -69,8 +69,8 @@ FLUSH TABLES;
 CHECK TABLE t1_will_crash;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1_will_crash	check	warning	Size of datafile is: 77       Should be: 7
+test.t1_will_crash	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1_will_crash	check	warning	Size of datafile is:        77       Should be: 7
 test.t1_will_crash	check	error	Corrupt
 REPAIR TABLE t1_will_crash;
 Table	Op	Msg_type	Msg_text
@@ -104,8 +104,8 @@ FLUSH TABLES;
 CHECK TABLE t1_will_crash;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1_will_crash	check	warning	Size of datafile is: 28       Should be: 7
+test.t1_will_crash	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1_will_crash	check	warning	Size of datafile is:        28       Should be: 7
 test.t1_will_crash	check	error	Partition p1 returned error
 test.t1_will_crash	check	error	Corrupt
 REPAIR TABLE t1_will_crash;
@@ -134,16 +134,16 @@ test.t1_will_crash	check	status	OK
 ALTER TABLE t1_will_crash CHECK PARTITION p0, p1;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1_will_crash	check	warning	Size of datafile is: 28       Should be: 7
+test.t1_will_crash	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1_will_crash	check	warning	Size of datafile is:        28       Should be: 7
 test.t1_will_crash	check	error	Partition p1 returned error
 test.t1_will_crash	check	error	Corrupt
 ALTER TABLE t1_will_crash CHECK PARTITION p1, p2;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	Table is marked as crashed
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1_will_crash	check	warning	Size of datafile is: 28       Should be: 7
+test.t1_will_crash	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1_will_crash	check	warning	Size of datafile is:        28       Should be: 7
 test.t1_will_crash	check	error	Partition p1 returned error
 test.t1_will_crash	check	error	Corrupt
 ALTER TABLE t1_will_crash REPAIR PARTITION p0, p2;
@@ -195,8 +195,8 @@ FLUSH TABLES;
 CHECK TABLE t1_will_crash;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1_will_crash	check	warning	Size of datafile is: 14       Should be: 7
+test.t1_will_crash	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1_will_crash	check	warning	Size of datafile is:        14       Should be: 7
 test.t1_will_crash	check	error	Subpartition p1sp0 returned error
 test.t1_will_crash	check	error	Corrupt
 REPAIR TABLE t1_will_crash;
@@ -225,16 +225,16 @@ test.t1_will_crash	check	status	OK
 ALTER TABLE t1_will_crash CHECK PARTITION all;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1_will_crash	check	warning	Size of datafile is: 14       Should be: 7
+test.t1_will_crash	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1_will_crash	check	warning	Size of datafile is:        14       Should be: 7
 test.t1_will_crash	check	error	Subpartition p1sp0 returned error
 test.t1_will_crash	check	error	Corrupt
 ALTER TABLE t1_will_crash CHECK PARTITION p1;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	Table is marked as crashed
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	error	Size of indexfile is: 1024        Should be: 2048
-test.t1_will_crash	check	warning	Size of datafile is: 14       Should be: 7
+test.t1_will_crash	check	error	Size of indexfile is:     1024        Should be: 2048
+test.t1_will_crash	check	warning	Size of datafile is:        14       Should be: 7
 test.t1_will_crash	check	error	Subpartition p1sp0 returned error
 test.t1_will_crash	check	error	Corrupt
 ALTER TABLE t1_will_crash REPAIR PARTITION p0;
@@ -331,7 +331,7 @@ test.t1_will_crash	optimize	warning	Number of rows changed from 8 to 7
 test.t1_will_crash	optimize	status	OK
 CHECK TABLE t1_will_crash;
 Table	Op	Msg_type	Msg_text
-test.t1_will_crash	check	error	Size of datafile is: 0         Should be: 164
+test.t1_will_crash	check	error	Size of datafile is:         0         Should be: 164
 test.t1_will_crash	check	error	Partition p0 returned error
 test.t1_will_crash	check	error	Corrupt
 REPAIR TABLE t1_will_crash;
@@ -406,7 +406,7 @@ ALTER TABLE t1_will_crash CHECK PARTITION p4;
 Table	Op	Msg_type	Msg_text
 test.t1_will_crash	check	warning	Table is marked as crashed and last repair failed
 test.t1_will_crash	check	warning	1 client is using or hasn't closed the table properly
-test.t1_will_crash	check	warning	Size of datafile is: 368       Should be: 252
+test.t1_will_crash	check	warning	Size of datafile is:       368       Should be: 252
 test.t1_will_crash	check	error	Found 4 keys of 3
 test.t1_will_crash	check	error	Partition p4 returned error
 test.t1_will_crash	check	error	Corrupt
@@ -419,7 +419,7 @@ FLUSH TABLES;
 # replacing p6 with a crashed MYD file (2) (splitted dynamic record)
 ALTER TABLE t1_will_crash CHECK PARTITION p6;
 Table	Op	Msg_type	Msg_text
-test.t1_will_crash	check	warning	Size of datafile is: 868       Should be: 604
+test.t1_will_crash	check	warning	Size of datafile is:       868       Should be: 604
 test.t1_will_crash	check	error	Unexpected byte: 0 at link: 340
 test.t1_will_crash	check	error	Partition p6 returned error
 test.t1_will_crash	check	error	Corrupt
@@ -472,9 +472,9 @@ partition	b	a
 SET @@optimizer_switch=@save_optimizer_switch;
 ALTER TABLE t1_will_crash CHECK PARTITION p6;
 Table	Op	Msg_type	Msg_text
-test.t1_will_crash	check	warning	Size of datafile is: 868       Should be: 604
-test.t1_will_crash	check	error	Record-count is not ok; is 8   Should be: 7
-test.t1_will_crash	check	warning	Found 10 key parts. Should be: 7
+test.t1_will_crash	check	warning	Size of datafile is:       868       Should be: 604
+test.t1_will_crash	check	error	Record-count is not ok; is          8   Should be: 7
+test.t1_will_crash	check	warning	Found         10 key parts. Should be: 7
 test.t1_will_crash	check	error	Partition p6 returned error
 test.t1_will_crash	check	error	Corrupt
 ALTER TABLE t1_will_crash REPAIR PARTITION p6;

strings/my_vsnprintf.c

@@ -224,12 +224,27 @@ static char *backtick_string(CHARSET_INFO *cs, char *to, const char *end,
 */
 
 static char *process_str_arg(CHARSET_INFO *cs, char *to, const char *end,
-                             size_t width, char *par, uint print_type,
-                             my_bool nice_cut)
+                             longlong length_arg, size_t width, char *par,
+                             uint print_type, my_bool nice_cut)
 {
   int well_formed_error;
   uint dots= 0;
   size_t plen, left_len= (size_t) (end - to) + 1, slen=0;
+  my_bool left_fill= 1;
+  size_t length;
+
+  /*
+    The sign of the length argument specific the string should be right
+    or left adjusted
+  */
+  if (length_arg < 0)
+  {
+    length= (size_t) -length_arg;
+    left_fill= 0;
+  }
+  else
+    length= (size_t) length_arg;
+
   if (!par)
     par = (char*) "(null)";
 
@@ -239,7 +254,10 @@ static char *process_str_arg(CHARSET_INFO *cs, char *to, const char *end,
     if (plen > width)
       plen= width;
     if (left_len <= plen)
+    {
       plen = left_len - 1;
+      length= plen;
+    }
     if ((slen > plen))
     {
       if (plen < 3)
@@ -259,24 +277,34 @@ static char *process_str_arg(CHARSET_INFO *cs, char *to, const char *end,
     plen= slen= strnlen(par, width);
     dots= 0;
     if (left_len <= plen)
+    {
       plen = left_len - 1;
+      length= plen;
+    }
   }
 
   plen= my_well_formed_length(cs, par, par + plen, width, &well_formed_error);
   if (print_type & ESCAPED_ARG)
   {
+    const char *org_to= to;
     to= backtick_string(cs, to, end, par, plen + dots, '`', MY_TEST(dots));
+    plen= (size_t) (to - org_to);
     dots= 0;
   }
   else
-    to= strnmov(to,par,plen);
-
-  if (dots)
   {
-    for (; dots; dots--)
-      *(to++)= '.';
-    *(to)= 0;
+    if (left_fill)
+    {
+      if (plen + dots < length)
+        to= strfill(to, length - plen - dots, ' ');
+    }
+    to= strnmov(to,par,plen);
+    if (dots)
+      to= strfill(to, dots, '.');
   }
+
+  if (!left_fill && plen + dots < length)
+    to= strfill(to, length - plen - dots, ' ');
   return to;
 }
 
@@ -494,11 +522,16 @@ static char *process_args(CHARSET_INFO *cs, char *to, char *end,
       case 's':
       case 'T':
       {
+        longlong min_field_width;
         char *par= args_arr[print_arr[i].arg_idx].str_arg;
         width= (print_arr[i].flags & WIDTH_ARG)
           ? (size_t)args_arr[print_arr[i].width].longlong_arg
           : print_arr[i].width;
-        to= process_str_arg(cs, to, end, width, par, print_arr[i].flags,
+        min_field_width= (print_arr[i].flags & LENGTH_ARG)
+          ? args_arr[print_arr[i].length].longlong_arg
+          : (longlong) print_arr[i].length;
+        to= process_str_arg(cs, to, end, min_field_width, width, par,
+                            print_arr[i].flags,
                             (print_arr[i].arg_type == 'T'));
         break;
       }
@@ -565,7 +598,7 @@ static char *process_args(CHARSET_INFO *cs, char *to, char *end,
           *to++= ' ';
           *to++= '"';
           my_strerror(errmsg_buff, sizeof(errmsg_buff), (int) larg);
-          to= process_str_arg(cs, to, real_end, width, errmsg_buff,
+          to= process_str_arg(cs, to, real_end, 0, width, errmsg_buff,
                               print_arr[i].flags, 1);
           if (real_end > to) *to++= '"';
         }
@@ -693,7 +726,8 @@ size_t my_vsnprintf_ex(CHARSET_INFO *cs, char *to, size_t n,
     if (*fmt == 's' || *fmt == 'T')			/* String parameter */
     {
       reg2 char *par= va_arg(ap, char *);
-      to= process_str_arg(cs, to, end, width, par, print_type, (*fmt == 'T'));
+      to= process_str_arg(cs, to, end, (longlong) length, width, par,
+                          print_type, (*fmt == 'T'));
       continue;
     }
     else if (*fmt == 'b')				/* Buffer parameter */
@@ -751,7 +785,7 @@ size_t my_vsnprintf_ex(CHARSET_INFO *cs, char *to, size_t n,
         *to++= ' ';
         *to++= '"';
         my_strerror(errmsg_buff, sizeof(errmsg_buff), (int) larg);
-        to= process_str_arg(cs, to, real_end, width, errmsg_buff,
+        to= process_str_arg(cs, to, real_end, 0, width, errmsg_buff,
                             print_type, 1);
         if (real_end > to) *to++= '"';
       }

unittest/mysys/my_vsnprintf-t.c

@@ -61,7 +61,7 @@ static void test_many(const char **res, const char *fmt, ...)
 
 int main(void)
 {
-  plan(47);
+  plan(48);
 
   test1("Constant string",
         "Constant string");
@@ -96,8 +96,11 @@ int main(void)
   test1("Flag '0' works <0006>",
         "Flag '0' works <%04d>", 6);
 
-  test1("Width is ignored for strings <x> <y>",
-        "Width is ignored for strings <%04s> <%5s>", "x", "y");
+  test1("Width for strings <   x> <    y>",
+        "Width for strings <%04s> <%5s>", "x", "y");
+
+  test1("Negative width is ignored for strings <   x> <    y>",
+        "Negative width is ignored for strings <%-4s> <%-5s>", "x", "y");
 
   test1("Precision works for strings <abcde>",
         "Precision works for strings <%.5s>", "abcdef!");