MDEV-34776 Assertion failure in Item_string::do_build_clone

Added missed methods to Item_string child.

mysql-test/main/item_types.result

@@ -35,5 +35,12 @@ SELECT * FROM t WHERE a=b'';
 a
 drop view t;
 #
+# MDEV-34776: Assertion failure in Item_string::do_build_clone
+#
+CREATE VIEW v AS SELECT version() AS f;
+SELECT * FROM v WHERE f = '10.5.20';
+f
+drop view v;
+#
 # End of 10.5 tests
 #

mysql-test/main/item_types.test

@@ -38,6 +38,14 @@ CREATE VIEW t AS SELECT 1 AS a;
 SELECT * FROM t WHERE a=b'';
 drop view t;
 
+--echo #
+--echo # MDEV-34776: Assertion failure in Item_string::do_build_clone
+--echo #
+
+CREATE VIEW v AS SELECT version() AS f;
+SELECT * FROM v WHERE f = '10.5.20';
+drop view v;
+
 --echo #
 --echo # End of 10.5 tests
 --echo #

sql/item.h

@@ -4719,6 +4719,9 @@ class Item_string_sys :public Item_string
   Item_string_sys(THD *thd, const char *str):
     Item_string(thd, str, (uint) strlen(str), system_charset_info)
   { }
+  Item *do_get_copy(THD *thd) const override
+  { return get_item_copy<Item_string_sys>(thd, this); }
+  Item *do_build_clone(THD *thd) const override { return get_copy(thd); }
 };
 
 
@@ -4733,6 +4736,9 @@ class Item_string_ascii :public Item_string
     Item_string(thd, str, (uint) strlen(str), &my_charset_latin1,
                 DERIVATION_COERCIBLE, MY_REPERTOIRE_ASCII)
   { }
+  Item *do_get_copy(THD *thd) const override
+  { return get_item_copy<Item_string_ascii>(thd, this); }
+  Item *do_build_clone(THD *thd) const override { return get_copy(thd); }
 };
 
 
@@ -4769,6 +4775,9 @@ class Item_static_string_func :public Item_string
     // require fix_fields() to be re-run for every statement.
     return mark_unsupported_function(func_name.str, arg, VCOL_TIME_FUNC);
   }
+  Item *do_get_copy(THD *thd) const override
+  { return get_item_copy<Item_static_string_func>(thd, this); }
+  Item *do_build_clone(THD *thd) const override { return get_copy(thd); }
 };
 
 
@@ -4786,6 +4795,9 @@ class Item_partition_func_safe_string: public Item_string
   {
     return mark_unsupported_function("safe_string", arg, VCOL_IMPOSSIBLE);
   }
+  Item *do_get_copy(THD *thd) const override
+  { return get_item_copy<Item_partition_func_safe_string>(thd, this); }
+  Item *do_build_clone(THD *thd) const override { return get_copy(thd); }
 };