Fix for BUG#15921: DROP TRIGGER - can't be drop trigger created

in older version.

The problem is that TRN-files created in "old" versions contain
junk in trigger_table field, which is not acceptable in "new" versions.

sql/parse_file.cc

@@ -533,7 +533,7 @@ parse_string(char *ptr, char *end, MEM_ROOT *mem_root, LEX_STRING *str)
   read escaped string from ptr to eol in already allocated str
 
   SYNOPSIS
-    parse_escaped_string()
+    read_escaped_string()
     ptr		- pointer on string beginning
     eol		- pointer on character after end of string
     str		- target string
@@ -604,7 +604,7 @@ read_escaped_string(char *ptr, char *eol, LEX_STRING *str)
     #	- pointer on symbol after string
 */
 
-static char *
+char *
 parse_escaped_string(char *ptr, char *end, MEM_ROOT *mem_root, LEX_STRING *str)
 {
   char *eol= strchr(ptr, '\n');
@@ -622,7 +622,7 @@ parse_escaped_string(char *ptr, char *end, MEM_ROOT *mem_root, LEX_STRING *str)
   parse '' delimited escaped string
 
   SYNOPSIS
-    parse_escaped_string()
+    parse_quoted_escaped_string()
     ptr		- pointer on string beginning
     end		- pointer on symbol after parsed string end (still owned
 		  by buffer and can be accessed

sql/parse_file.h

@@ -72,6 +72,9 @@ bool get_file_options_ulllist(char *&ptr, char *end, char *line,
                               gptr base, File_option *parameter,
                               MEM_ROOT *mem_root);
 
+char *
+parse_escaped_string(char *ptr, char *end, MEM_ROOT *mem_root, LEX_STRING *str);
+
 class File_parser;
 File_parser *sql_parse_prepare(const LEX_STRING *file_name,
 			       MEM_ROOT *mem_root, bool bad_format_errors);

sql/sql_trigger.cc

@@ -109,10 +109,6 @@ const LEX_STRING trg_event_type_names[]=
 
 static TABLE_LIST *add_table_for_trigger(THD *thd, sp_name *trig);
 
-bool handle_old_incorrect_sql_modes(char *&unknown_key, gptr base,
-                                    MEM_ROOT *mem_root,
-                                    char *end, gptr hook_data);
-
 class Handle_old_incorrect_sql_modes_hook: public Unknown_key_hook
 {
 private:
@@ -125,6 +121,20 @@ public:
                                       MEM_ROOT *mem_root, char *end);
 };
 
+class Handle_old_incorrect_trigger_table_hook: public Unknown_key_hook
+{
+public:
+  Handle_old_incorrect_trigger_table_hook(char *file_path,
+                                          LEX_STRING *trigger_table_arg)
+    :path(file_path), trigger_table_value(trigger_table_arg)
+  {};
+  virtual bool process_unknown_string(char *&unknown_key, gptr base,
+                                      MEM_ROOT *mem_root, char *end);
+private:
+  char *path;
+  LEX_STRING *trigger_table_value;
+};
+
 /*
   Create or drop trigger for table.
 
@@ -1130,6 +1140,9 @@ static TABLE_LIST *add_table_for_trigger(THD *thd, sp_name *trig)
   LEX_STRING path;
   File_parser *parser;
   struct st_trigname trigname;
+  Handle_old_incorrect_trigger_table_hook trigger_table_hook(
+                                          path_buff, &trigname.trigger_table);
+  
   DBUG_ENTER("add_table_for_trigger");
 
   strxnmov(path_buff, FN_REFLEN, mysql_data_home, "/", trig->m_db.str, "/",
@@ -1155,7 +1168,7 @@ static TABLE_LIST *add_table_for_trigger(THD *thd, sp_name *trig)
 
   if (parser->parse((gptr)&trigname, thd->mem_root,
                     trigname_file_parameters, 1,
-                    &file_parser_dummy_hook))
+                    &trigger_table_hook))
     DBUG_RETURN(0);
 
   /* We need to reset statement table list to be PS/SP friendly. */
@@ -1542,7 +1555,7 @@ Handle_old_incorrect_sql_modes_hook::process_unknown_string(char *&unknown_key,
                                                             MEM_ROOT *mem_root,
                                                             char *end)
 {
-  DBUG_ENTER("handle_old_incorrect_sql_modes");
+  DBUG_ENTER("Handle_old_incorrect_sql_modes_hook::process_unknown_string");
   DBUG_PRINT("info", ("unknown key:%60s", unknown_key));
 
   if (unknown_key + INVALID_SQL_MODES_LENGTH + 1 < end &&
@@ -1571,3 +1584,44 @@ Handle_old_incorrect_sql_modes_hook::process_unknown_string(char *&unknown_key,
   }
   DBUG_RETURN(FALSE);
 }
+
+/*
+  Trigger BUG#15921 compatibility hook. For details see
+  Handle_old_incorrect_sql_modes_hook::process_unknown_string().
+*/
+
+#define INVALID_TRIGGER_TABLE_LENGTH 15
+
+bool
+Handle_old_incorrect_trigger_table_hook::
+process_unknown_string(char *&unknown_key, gptr base, MEM_ROOT *mem_root,
+                       char *end)
+{
+  DBUG_ENTER("Handle_old_incorrect_trigger_table_hook::process_unknown_string");
+  DBUG_PRINT("info", ("unknown key:%60s", unknown_key));
+
+  if (unknown_key + INVALID_TRIGGER_TABLE_LENGTH + 1 < end &&
+      unknown_key[INVALID_TRIGGER_TABLE_LENGTH] == '=' &&
+      !memcmp(unknown_key, STRING_WITH_LEN("trigger_table")))
+  {
+    char *ptr= unknown_key + INVALID_TRIGGER_TABLE_LENGTH + 1;
+
+    DBUG_PRINT("info", ("trigger_table affected by BUG#15921 detected"));
+    push_warning_printf(current_thd,
+                        MYSQL_ERROR::WARN_LEVEL_NOTE,
+                        ER_OLD_FILE_FORMAT,
+                        ER(ER_OLD_FILE_FORMAT),
+                        (char *)path, "TRIGGER");
+
+    if (!(ptr= parse_escaped_string(ptr, end, mem_root, trigger_table_value)))
+    {
+      my_error(ER_FPARSER_ERROR_IN_PARAMETER, MYF(0), "trigger_table",
+               unknown_key);
+      DBUG_RETURN(TRUE);
+    }
+
+    /* Set parsing pointer to the last symbol of string (\n). */
+    unknown_key= ptr-1;
+  }
+  DBUG_RETURN(FALSE);
+}