MDEV-29344: engines/iuds.insert_time cannot run with PS protocol (syntax error)

The syntax error produced on running the test engines/iuds.insert_time
in PS-mode was caused by presence of the C-Style comment containing
the single quote at the end of SQL statement, something like
the following one:
  /* doesn't throw error */;
Presence of the single quote was interpreted by mysqltest utility as
indication of real string literal, that resulted in consuming every
characters following that mark as a literal, including the delimiter
character ';'. It led to concatenation of lines into a single
multi-statement that was sent from mysqltest to MariaDB server for
processing. In case mysqltest is run in regular mode (that is,
not PS-mode), multi-statement is handled successfully on server side,
but in case PS-mode is on, multi-statement is supplied in COM_STMT_PREPARE
that caused the parsing error since multi-statements is not supported by
statement prepare command.

To fix the issue, in case mysqltest encounters the C-Style comment
is should switch to reading next following characters without any
processing until it hit the closing C-style comment marks '*/',
with one exception if the sequence of characters '/*' followed by
the exclamation mark, that means the hint introducer has been read.

client/mysqltest.cc

@@ -6744,7 +6744,7 @@ int read_line()
   my_bool have_slash= FALSE;
   
   enum {R_NORMAL, R_Q, R_SLASH_IN_Q,
-        R_COMMENT, R_LINE_START} state= R_LINE_START;
+        R_COMMENT, R_LINE_START, R_CSTYLE_COMMENT} state= R_LINE_START;
   DBUG_ENTER("read_line");
 
   *p= 0;
@@ -6831,9 +6831,23 @@ int read_line()
 	  state= R_Q;
 	}
       }
+      else if (c == '*' && last_char == '/')
+      {
+        state= R_CSTYLE_COMMENT;
+        break;
+      }
       have_slash= is_escape_char(c, last_quote);
       break;
 
+    case R_CSTYLE_COMMENT:
+      if (c == '!')
+        // Got the hint introducer '/*!'. Switch to normal processing of
+        // next following characters
+        state= R_NORMAL;
+      else if (c == '/' && last_char == '*')
+        state= R_NORMAL;
+      break;
+
     case R_COMMENT:
       if (c == '\n')
       {

mysql-test/main/mysqltest.result

@@ -989,4 +989,13 @@ select "foo\""bar";
 foo\"bar
 foo\"bar
 set sql_mode=default;
+#
+# MDEV-29344: engines/iuds.insert_time cannot run with PS protocol (syntax error)
+#
+SELECT 1 /* doesn't throw error */;
+1
+1
+SELECT 1 /* doesn't throw error */;
+1
+1
 End of tests

mysql-test/main/mysqltest.test

@@ -2954,6 +2954,12 @@ set sql_mode=no_backslash_escapes;
 select "foo\""bar";
 set sql_mode=default;
 
+--echo #
+--echo # MDEV-29344: engines/iuds.insert_time cannot run with PS protocol (syntax error)
+--echo #
+SELECT 1 /* doesn't throw error */;
+SELECT 1 /* doesn't throw error */;
+
 --echo End of tests
 
 # Wait till we reached the initial number of concurrent sessions

mysql-test/suite/engines/iuds/r/insert_time.result

@@ -5073,10 +5073,14 @@ ERROR 23000: Duplicate entry '825:23:00' for key 'c2'
 INSERT INTO t3(c1,c2) VALUES('34 9:23','34 9:23') /* throws error as row exists with c1='34 9:23',c2='34 9:23' */;
 ERROR 23000: Duplicate entry '825:23:00-825:23:00' for key 'idx'
 INSERT IGNORE INTO t1(c1,c2) VALUES('10:22:33','10:22:34') /* doesn't throw error */;
+Warnings:
+Warning	1062	Duplicate entry '10:22:33' for key 'PRIMARY'
 INSERT IGNORE INTO t2(c1,c2) VALUES('12:34:56.78','12:34:56.78') /*doesn't throw error */;
 Warnings:
 Warning	1062	Duplicate entry '12:34:56-12:34:56' for key 'PRIMARY'
 INSERT IGNORE INTO t1(c1,c2) VALUES('10:22:34','34 9:23') /*doesn't throw error */;
+Warnings:
+Warning	1062	Duplicate entry '825:23:00' for key 'c2'
 INSERT IGNORE INTO t3(c1,c2) VALUES('34 9:23','34 9:23') /*doesn't throw error */;
 Warnings:
 Warning	1062	Duplicate entry '825:23:00-825:23:00' for key 'idx'