Bug #30832: Assertion + crash with select name_const('test', now());

The NAME_CONST function is required to work correctly with constants only.
When executed with functions that return types other than those returned by
Item::field_type (string, int, decimal, or real), the result gets cast to
one of those types. This cannot happen for constants.
Fixed by only allowing constants as arguments to NAME_CONST.

mysql-test/r/func_misc.result

@@ -185,4 +185,20 @@ ERROR 21000: Operand should contain 1 column(s)
 drop table table_26093;
 drop function func_26093_a;
 drop function func_26093_b;
+SELECT NAME_CONST('test', NOW());
+ERROR HY000: Incorrect arguments to NAME_CONST
+SELECT NAME_CONST('test', UPPER('test'));
+ERROR HY000: Incorrect arguments to NAME_CONST
+SELECT NAME_CONST('test', NULL);
+test
+NULL
+SELECT NAME_CONST('test', 1);
+test
+1
+SELECT NAME_CONST('test', 1.0);
+test
+1.0
+SELECT NAME_CONST('test', 'test');
+test
+test
 End of 5.0 tests

mysql-test/t/func_misc.test

@@ -189,4 +189,18 @@ drop table table_26093;
 drop function func_26093_a;
 drop function func_26093_b;
 
+#
+# Bug #30832: Assertion + crash with select name_const('test',now());
+#
+--error ER_WRONG_ARGUMENTS
+SELECT NAME_CONST('test', NOW());
+--error ER_WRONG_ARGUMENTS
+SELECT NAME_CONST('test', UPPER('test'));
+
+SELECT NAME_CONST('test', NULL);
+SELECT NAME_CONST('test', 1);
+SELECT NAME_CONST('test', 1.0);
+SELECT NAME_CONST('test', 'test');
+
 --echo End of 5.0 tests
+

sql/item.h

@@ -1112,6 +1112,8 @@ public:
   Item_name_const(Item *name_arg, Item *val):
     value_item(val), name_item(name_arg)
   {
+    if(!value_item->basic_const_item())
+      my_error(ER_WRONG_ARGUMENTS, MYF(0), "NAME_CONST");
     Item::maybe_null= TRUE;
   }