MDEV-34634 Types mismatch when cloning items causes debug assertion

New runtime diagnostic introduced with MDEV-34490 has detected
that `Item_int_with_ref` incorrectly returns an instance of its ancestor
class `Item_int`. This commit fixes that.

In addition, this commit reverts a part of the diagnostic related
to `clone_item()` checks. As it turned out, `clone_item()` is not required
to return an object of the same class as the cloned one. For example,
look at `Item_param::clone_item()`: it can return objects of `Item_null`,
`Item_int`, `Item_string`, etc, depending on the object state.
So the runtime type diagnostic is not applicable to `clone_item()` and
is disabled with this commit.

As the similar diagnostic failures are expected to appear again
in the future, this commit introduces a new test file in the main suite:
item_types.test, and new test cases may be added to this file

Reviewer: Oleksandr Byelkin <sanja@mariadb.com>

mysql-test/main/item_types.result

@@ -0,0 +1,16 @@
+#
+# MDEV-34634 Types mismatch when cloning items causes debug assertion
+#
+CREATE TABLE t1 (a DATETIME);
+SET optimizer_switch='derived_merge=off';
+SELECT * FROM (SELECT * FROM t1) AS t1 WHERE a='';
+a
+Warnings:
+Warning	1292	Truncated incorrect datetime value: ''
+DROP TABLE t1;
+CREATE TABLE t1 (c YEAR);
+CREATE TABLE t2 (c INT);
+SELECT * FROM t1 JOIN t2 ON t1.c=t2.c WHERE t1.c<=>5;
+c	c
+DROP TABLE t1, t2;
+SET optimizer_switch=default;

mysql-test/main/item_types.test

@@ -0,0 +1,15 @@
+--echo #
+--echo # MDEV-34634 Types mismatch when cloning items causes debug assertion
+--echo #
+
+CREATE TABLE t1 (a DATETIME);
+SET optimizer_switch='derived_merge=off';
+SELECT * FROM (SELECT * FROM t1) AS t1 WHERE a='';
+DROP TABLE t1;
+
+CREATE TABLE t1 (c YEAR);
+CREATE TABLE t2 (c INT);
+SELECT * FROM t1 JOIN t2 ON t1.c=t2.c WHERE t1.c<=>5;
+DROP TABLE t1, t2;
+
+SET optimizer_switch=default;

sql/item.cc

@@ -3847,7 +3847,7 @@ void Item_decimal::set_decimal_value(my_decimal *value_par)
 }
 
 
-Item *Item_decimal::do_clone_const_item(THD *thd) const
+Item *Item_decimal::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_decimal(thd, name.str, &decimal_value, decimals,
                                          max_length);
@@ -3868,7 +3868,7 @@ my_decimal *Item_float::val_decimal(my_decimal *decimal_value)
 }
 
 
-Item *Item_float::do_clone_const_item(THD *thd) const
+Item *Item_float::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_float(thd, name.str, value, decimals,
                                        max_length);
@@ -4032,7 +4032,7 @@ Item *Item_null::safe_charset_converter(THD *thd, CHARSET_INFO *tocs)
   return this;
 }
 
-Item *Item_null::do_clone_const_item(THD *thd) const
+Item *Item_null::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_null(thd, name.str);
 }
@@ -4873,7 +4873,7 @@ Item *Item_param::value_clone_item(THD *thd) const
 /* see comments in the header file */
 
 Item *
-Item_param::do_clone_const_item(THD *thd) const
+Item_param::clone_item(THD *thd) const
 {
   // There's no "default". See comments in Item_param::save_in_field().
   switch (state) {
@@ -6953,7 +6953,7 @@ int Item_string::save_in_field(Field *field, bool no_conversions)
 }
 
 
-Item *Item_string::do_clone_const_item(THD *thd) const
+Item *Item_string::clone_item(THD *thd) const
 {
   LEX_CSTRING val;
   str_value.get_value(&val);
@@ -7017,7 +7017,7 @@ int Item_int::save_in_field(Field *field, bool no_conversions)
 }
 
 
-Item *Item_int::do_clone_const_item(THD *thd) const
+Item *Item_int::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_int(thd, name.str, value, max_length, unsigned_flag);
 }
@@ -7046,7 +7046,7 @@ int Item_decimal::save_in_field(Field *field, bool no_conversions)
 }
 
 
-Item *Item_int_with_ref::do_clone_const_item(THD *thd) const
+Item *Item_int_with_ref::clone_item(THD *thd) const
 {
   DBUG_ASSERT(ref->const_item());
   /*
@@ -7142,7 +7142,7 @@ Item *Item_uint::neg(THD *thd)
 }
 
 
-Item *Item_uint::do_clone_const_item(THD *thd) const
+Item *Item_uint::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_uint(thd, name.str, value, max_length);
 }
@@ -7380,7 +7380,7 @@ void Item_date_literal::print(String *str, enum_query_type query_type)
 }
 
 
-Item *Item_date_literal::do_clone_const_item(THD *thd) const
+Item *Item_date_literal::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_date_literal(thd, &cached_time);
 }
@@ -7405,7 +7405,7 @@ void Item_datetime_literal::print(String *str, enum_query_type query_type)
 }
 
 
-Item *Item_datetime_literal::do_clone_const_item(THD *thd) const
+Item *Item_datetime_literal::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_datetime_literal(thd, &cached_time, decimals);
 }
@@ -7430,7 +7430,7 @@ void Item_time_literal::print(String *str, enum_query_type query_type)
 }
 
 
-Item *Item_time_literal::do_clone_const_item(THD *thd) const
+Item *Item_time_literal::clone_item(THD *thd) const
 {
   return new (thd->mem_root) Item_time_literal(thd, &cached_time, decimals);
 }
@@ -10389,7 +10389,7 @@ void Item_cache_temporal::store_packed(longlong val_arg, Item *example_arg)
 }
 
 
-Item *Item_cache_temporal::do_clone_const_item(THD *thd) const
+Item *Item_cache_temporal::clone_item(THD *thd) const
 {
   Item_cache *tmp= type_handler()->Item_get_cache(thd, this);
   Item_cache_temporal *item= static_cast<Item_cache_temporal*>(tmp);

sql/item.h

@@ -1698,21 +1698,17 @@ public:
   }
 
   /*
-    Clones the constant item
+    Clones the constant item (not necessary returning the same item type)
 
     Return value:
     - pointer to a clone of the Item
-    - nullptr if the item is not clonable */
-  Item *clone_const_item(THD *thd) const
-  {
-    Item *clone= do_clone_const_item(thd);
-    if (clone)
-    {
-      // Make sure the clone is of same type as this item
-      DBUG_ASSERT(typeid(*clone) == typeid(*this));
-    }
-    return clone;
-  }
+    - nullptr if the item is not clonable
+
+    Note: the clone may have item type different from this
+    (i.e., instance of another basic constant class may be returned).
+    For real clones look at build_clone()/get_copy() methods
+  */
+  virtual Item *clone_item(THD *thd) const { return nullptr; }
 
   virtual cond_result eq_cmp_result() const { return COND_OK; }
   inline uint float_length(uint decimals_par) const
@@ -2588,12 +2584,6 @@ protected:
     deep copies (clones) of the item where possible
   */
   virtual Item* do_build_clone(THD *thd) const = 0;
-
-  /*
-    Service function for public method clone_const_item(). See comments for
-    clone_const_item() above
-  */
-  virtual Item *do_clone_const_item(THD *thd) const { return nullptr; }
 };
 
 MEM_ROOT *get_thd_memroot(THD *thd);
@@ -3820,7 +3810,7 @@ public:
   const Type_handler *type_handler() const override
   { return &type_handler_null; }
   bool basic_const_item() const override { return true; }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   bool const_is_null() const override { return true; }
   bool is_null() override { return true; }
 
@@ -4270,7 +4260,7 @@ public:
     basic_const_item returned TRUE.
   */
   Item *safe_charset_converter(THD *thd, CHARSET_INFO *tocs) override;
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   void set_param_type_and_swap_value(Item_param *from);
 
   Rewritable_query_parameter *get_rewritable_query_parameter() override
@@ -4369,7 +4359,7 @@ public:
   String *val_str(String*) override;
   int save_in_field(Field *field, bool no_conversions) override;
   bool is_order_clause_position() const override { return true; }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   void print(String *str, enum_query_type query_type) override;
   Item *neg(THD *thd) override;
   uint decimal_precision() const override
@@ -4417,7 +4407,7 @@ public:
   Item_uint(THD *thd, ulonglong i): Item_int(thd, i, 10) {}
   Item_uint(THD *thd, const char *str_arg, longlong i, uint length);
   double val_real() override { return ulonglong2double((ulonglong)value); }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   Item *neg(THD *thd) override;
   uint decimal_precision() const override { return max_length; }
   Item *do_get_copy(THD *thd) const override
@@ -4468,7 +4458,7 @@ public:
   const my_decimal *const_ptr_my_decimal() const override
   { return &decimal_value; }
   int save_in_field(Field *field, bool no_conversions) override;
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   void print(String *str, enum_query_type query_type) override
   {
     decimal_value.to_string(&str_value);
@@ -4521,7 +4511,7 @@ public:
   }
   String *val_str(String*) override;
   my_decimal *val_decimal(my_decimal *) override;
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   Item *neg(THD *thd) override;
   void print(String *str, enum_query_type query_type) override;
   Item *do_get_copy(THD *thd) const override
@@ -4644,7 +4634,7 @@ public:
   int save_in_field(Field *field, bool no_conversions) override;
   const Type_handler *type_handler() const override
   { return &type_handler_varchar; }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   Item *safe_charset_converter(THD *thd, CHARSET_INFO *tocs) override
   {
     return const_charset_converter(thd, tocs, true);
@@ -5067,7 +5057,7 @@ public:
   {
     return cached_time.get_mysql_time();
   }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   longlong val_int() override
   {
     return update_null() ? 0 : cached_time.to_longlong();
@@ -5117,7 +5107,7 @@ public:
   {
     return cached_time.get_mysql_time();
   }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   longlong val_int() override { return cached_time.to_longlong(); }
   double val_real() override { return cached_time.to_double(); }
   String *val_str(String *to) override
@@ -5168,7 +5158,7 @@ public:
   {
     return cached_time.get_mysql_time();
   }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   longlong val_int() override
   {
     return update_null() ? 0 : cached_time.to_longlong();
@@ -5256,6 +5246,9 @@ public:
     cached_time.copy_to_mysql_time(ltime);
     return (null_value= false);
   }
+  Item *do_get_copy(THD *thd) const override
+  { return get_item_copy<Item_datetime_literal_for_invalid_dates>(thd, this); }
+  Item *do_build_clone(THD *thd) const override { return get_copy(thd); }
 };
 
 
@@ -6299,8 +6292,11 @@ public:
   {
     return ref->save_in_field(field, no_conversions);
   }
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   Item *real_item() override { return ref; }
+  Item *do_get_copy(THD *thd) const override
+  { return get_item_copy<Item_int_with_ref>(thd, this); }
+  Item *do_build_clone(THD *thd) const override { return get_copy(thd); }
 };
 
 #ifdef MYSQL_SERVER
@@ -7209,7 +7205,7 @@ public:
     is a constant and need not be optimized further.
     Important when storing packed datetime values.
   */
-  Item *do_clone_const_item(THD *thd) const override;
+  Item *clone_item(THD *thd) const override;
   Item *convert_to_basic_const_item(THD *thd) override;
   virtual Item *make_literal(THD *) =0;
 };

sql/sql_select.cc

@@ -16632,7 +16632,7 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
   if (can_change_cond_ref_to_const(func, right_item, left_item,
                                    field_value_owner, field, value))
   {
-    Item *tmp=value->clone_const_item(thd);
+    Item *tmp=value->clone_item(thd);
     if (tmp)
     {
       tmp->collation.set(right_item->collation);
@@ -16662,7 +16662,7 @@ change_cond_ref_to_const(THD *thd, I_List<COND_CMP> *save_list,
   else if (can_change_cond_ref_to_const(func, left_item, right_item,
                                         field_value_owner, field, value))
   {
-    Item *tmp= value->clone_const_item(thd);
+    Item *tmp= value->clone_item(thd);
     if (tmp)
     {
       tmp->collation.set(left_item->collation);