MDEV-19182 mysqldump not always handling SHOW CREATE TRIGGER failures correctly

only use SHOW TRIGGERS on old (< 5.1.21) servers, otherwise
always use SHOW CREATE TRIGGER and don't fallback.

client/mysqldump.c

@@ -3262,7 +3262,7 @@ static void dump_trigger_old(FILE *sql_file, MYSQL_RES *show_triggers_rs,
 
   char name_buff[NAME_LEN * 4 + 3];
   const char *xml_msg= "\nWarning! mysqldump being run against old server "
-                       "that does not\nsupport 'SHOW CREATE TRIGGERS' "
+                       "that does not\nsupport 'SHOW CREATE TRIGGER' "
                        "statement. Skipping..\n";
 
   DBUG_ENTER("dump_trigger_old");
@@ -3413,12 +3413,14 @@ static int dump_triggers_for_table(char *table_name, char *db_name)
 
   char       db_cl_name[MY_CS_NAME_SIZE];
   int        ret= TRUE;
+  /* Servers below 5.1.21 do not support SHOW CREATE TRIGGER */
+  const int  use_show_create_trigger= mysql_get_server_version(mysql) >= 50121;
 
   DBUG_ENTER("dump_triggers_for_table");
   DBUG_PRINT("enter", ("db: %s, table_name: %s", db_name, table_name));
 
-  if (path && !(sql_file= open_sql_file_for_table(table_name,
-                                                  O_WRONLY | O_APPEND)))
+  if (path &&
+      !(sql_file= open_sql_file_for_table(table_name, O_WRONLY | O_APPEND)))
     DBUG_RETURN(1);
 
   /* Do not use ANSI_QUOTES on triggers in dump */
@@ -3434,11 +3436,15 @@ static int dump_triggers_for_table(char *table_name, char *db_name)
 
   /* Get list of triggers. */
 
-  my_snprintf(query_buff, sizeof(query_buff),
-              "SELECT TRIGGER_NAME FROM INFORMATION_SCHEMA.TRIGGERS "
-              "WHERE EVENT_OBJECT_SCHEMA = DATABASE() AND "
-              "EVENT_OBJECT_TABLE = %s",
-              quote_for_equal(table_name, name_buff));
+  if (use_show_create_trigger)
+    my_snprintf(query_buff, sizeof(query_buff),
+                "SELECT TRIGGER_NAME FROM INFORMATION_SCHEMA.TRIGGERS "
+                "WHERE EVENT_OBJECT_SCHEMA = DATABASE() AND "
+                "EVENT_OBJECT_TABLE = %s",
+                quote_for_equal(table_name, name_buff));
+  else
+    my_snprintf(query_buff, sizeof(query_buff), "SHOW TRIGGERS LIKE %s",
+                quote_for_like(table_name, name_buff));
 
   if (mysql_query_with_error_report(mysql, &show_triggers_rs, query_buff))
     goto done;
@@ -3454,35 +3460,28 @@ static int dump_triggers_for_table(char *table_name, char *db_name)
 
   while ((row= mysql_fetch_row(show_triggers_rs)))
   {
-
-    my_snprintf(query_buff, sizeof (query_buff),
-                "SHOW CREATE TRIGGER %s",
-                quote_name(row[0], name_buff, TRUE));
-
-    if (mysql_query(mysql, query_buff))
+    if (use_show_create_trigger)
     {
-      /*
-        mysqldump is being run against old server, that does not support
-        SHOW CREATE TRIGGER statement. We should use SHOW TRIGGERS output.
+      MYSQL_RES *show_create_trigger_rs;
 
-        NOTE: the dump may be incorrect, as old SHOW TRIGGERS does not
-        provide all the necessary information to restore trigger properly.
-      */
+      my_snprintf(query_buff, sizeof (query_buff), "SHOW CREATE TRIGGER %s",
+                  quote_name(row[0], name_buff, TRUE));
 
-      dump_trigger_old(sql_file, show_triggers_rs, &row, table_name);
-    }
-    else
-    {
-      MYSQL_RES *show_create_trigger_rs= mysql_store_result(mysql);
-
-      int error= (!show_create_trigger_rs ||
-                  dump_trigger(sql_file, show_create_trigger_rs, db_name,
-                               db_cl_name));
-      mysql_free_result(show_create_trigger_rs);
-      if (error)
+      if (mysql_query_with_error_report(mysql, &show_create_trigger_rs,
+                                        query_buff))
         goto done;
+      else
+      {
+        int error= (!show_create_trigger_rs ||
+                    dump_trigger(sql_file, show_create_trigger_rs, db_name,
+                                 db_cl_name));
+        mysql_free_result(show_create_trigger_rs);
+        if (error)
+          goto done;
+      }
     }
-    
+    else
+      dump_trigger_old(sql_file, show_triggers_rs, &row, table_name);
   }
 
   if (opt_xml)

mysql-test/r/mysqldump-compat.result

@@ -2,3 +2,7 @@ CREATE DATABASE mysqldump_30126;
 USE mysqldump_30126;
 CREATE TABLE t1 (c1 int);
 DROP DATABASE mysqldump_30126;
+use test;
+create table t1 (a int);
+create trigger tr after insert on t1 for each row set @a=1;
+drop table t1;

mysql-test/t/mysqldump-compat.test

@@ -15,3 +15,16 @@ CREATE TABLE t1 (c1 int);
 DROP DATABASE mysqldump_30126;
 
 --remove_file $file
+use test;
+
+#
+# MDEV-19182 mysqldump not always handling SHOW CREATE TRIGGER failures correctly
+#
+create table t1 (a int);
+create trigger tr after insert on t1 for each row set @a=1;
+let $datadir=`select @@datadir`;
+move_file $datadir/test/tr.TRN $datadir/test/tr-1.TRN;
+error 2;
+exec $MYSQL_DUMP test t1 >/dev/null;
+move_file $datadir/test/tr-1.TRN $datadir/test/tr.TRN;
+drop table t1;