Fix for bug#44860: ALTER TABLE on view crashes server

Problem: executing queries like "ALTER TABLE view1;" we don't
check new view's name (which is not specified),
that leads to server crash.

Fix: do nothing (to be consistent with the behaviour for tables) 
in such cases.

mysql-test/r/view.result

@@ -3836,6 +3836,14 @@ call p();
 call p();
 drop view a;
 drop procedure p;
+#
+# Bug #44860: ALTER TABLE on view crashes server
+#
+CREATE TABLE t1 (a INT);
+CREATE VIEW v1 AS SELECT a FROM t1;
+ALTER TABLE v1;
+DROP VIEW v1;
+DROP TABLE t1;
 # -----------------------------------------------------------------
 # -- End of 5.1 tests.
 # -----------------------------------------------------------------

mysql-test/t/view.test

@@ -3859,6 +3859,17 @@ drop procedure p;
 
 ###########################################################################
 
+
+--echo #
+--echo # Bug #44860: ALTER TABLE on view crashes server
+--echo #
+CREATE TABLE t1 (a INT);
+CREATE VIEW v1 AS SELECT a FROM t1;
+ALTER TABLE v1;
+DROP VIEW v1;
+DROP TABLE t1;
+
+
 --echo # -----------------------------------------------------------------
 --echo # -- End of 5.1 tests.
 --echo # -----------------------------------------------------------------

sql/sql_rename.cc

@@ -261,6 +261,8 @@ do_rename(THD *thd, TABLE_LIST *ren_table, char *new_db, char *new_table_name,
     old_alias= ren_table->table_name;
     new_alias= new_table_name;
   }
+  DBUG_ASSERT(new_alias);
+
   build_table_filename(name, sizeof(name),
                        new_db, new_alias, reg_ext, 0);
   if (!access(name,F_OK))

sql/sql_table.cc

@@ -6139,6 +6139,20 @@ bool mysql_alter_table(THD *thd,char *new_db, char *new_name,
   /* Sic: there is a race here */
   if (frm_type == FRMTYPE_VIEW && !(alter_info->flags & ~ALTER_RENAME))
   {
+    /*
+      The following branch handles "ALTER VIEW v1 /no arguments/;"
+      This feature is not documented one. 
+      However, before "OPTIMIZE TABLE t1;" was implemented, 
+      ALTER TABLE with no alter_specifications was used to force-rebuild
+      the table. That's why this grammar is allowed. That's why we ignore
+      it for views. So just do nothing in such a case.
+    */
+    if (!new_name)
+    {
+      my_ok(thd);
+      DBUG_RETURN(FALSE);
+    }
+
     /*
       Avoid problems with a rename on a table that we have locked or
       if the user is trying to to do this in a transcation context