MDEV-16309 Split ::create_tmp_field() into virtual methods in Item

Detailed: changes:
1. Moving Field specific code into new methods on Field:
   - Field *Field::create_tmp_field(...)
   - virtual void init_for_tmp_table(...)

2. Removing virtual Item::create_tmp_field().
   Adding instead a new virtual method Item::create_tmp_field_ex().

   Note, a virtual create_tmp_field() still exists, but only for Item_sum.
   This resembles 10.0 code structure. Perhaps create_tmp_field() should
   be removed from Item_sum and Item_sum descendants should override
   create_tmp_field_ex() directly. This can be done in a separate commit.

3. Adding helper classes Tmp_field_src and Tmp_field_param,
   to make the API for Item::create_tmp_field_ex() smaller
   and easier to extend in the future.

4. Decomposing the public function create_tmp_field() into
   virtual implementations for Item and a number of its descendants:
   - Item_basic_value
   - Item_sp_variable
   - Item_name_const
   - Item_result_field
   - Item_field
   - Item_ref
   - Item_type_holder
   - Item_row
   - Item_func_sp
   - Item_func_user_var
   - Item_sum
   - Item_sum_field
   - Item_proc

5. Adding DBUG_ASSERT-only virtual implementations for
   Item types that should not appear in create_tmp_table_ex(),
   for easier debugging:
   - Item_nodeset_func
   - Item_nodeset_to_const_comparator
   - Item_null_result
   - Item_copy
   - Item_ident_for_show
   - Item_user_var_as_out_param

6. Moving public function create_tmp_field_from_field()
   as a method to Item_field.

7. Removing Item::set_result_field(). It's not needed any more.

8. Cleanup: Removing the enum value "EXPR_CACHE_ITEM",
   as it's not used for a very long time.

1 files changed, 45 insertions, 0 deletions

diff --git a/mysql-test/main/func_analyse.result b/mysql-test/main/func_analyse.result
index 1e78e603bca..068693bd028 100644
--- a/mysql-test/main/func_analyse.result
+++ b/mysql-test/main/func_analyse.result
@@ -171,3 +171,48 @@ SELECT (SELECT 1 FROM t1 PROCEDURE ANALYSE()) FROM t2;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'PROCEDURE ANALYSE()) FROM t2' at line 1
 SELECT ((SELECT 1 FROM t1 PROCEDURE ANALYSE())) FROM t2;
 ERROR 42000: You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near 'PROCEDURE ANALYSE())) FROM t2' at line 1
+#
+# Start of 10.4 tests
+#
+#
+# MDEV-16309 Split ::create_tmp_field() into virtual methods in Item
+#
+CREATE TABLE t1 (a INT);
+INSERT INTO t1 VALUES (1),(2),(3);
+BEGIN NOT ATOMIC
+DECLARE rec ROW(Field_name TEXT,
+Min_value TEXT,
+Max_value TEXT,
+Min_length TEXT,
+Max_length TEXT,
+Empties_or_zeros TEXT,
+Nulls TEXT,
+Avg_value_or_avg_length TEXT,
+Std TEXT,
+Optimal_fieldtype TEXT);
+DECLARE c CURSOR FOR SELECT * FROM t1 PROCEDURE analyse();
+OPEN c;
+FETCH c INTO rec;
+CLOSE c;
+SELECT rec.field_name,
+rec.Min_value, rec.Max_value,
+rec.Min_length, rec. Max_length,
+rec.Empties_or_zeros, rec.Nulls,
+rec.Avg_value_or_avg_length, rec.Std,
+rec.Optimal_fieldtype;
+END;
+$$
+rec.field_name	test.t1.a
+rec.Min_value	1
+rec.Max_value	3
+rec.Min_length	1
+rec. Max_length	1
+rec.Empties_or_zeros	0
+rec.Nulls	0
+rec.Avg_value_or_avg_length	2.0000
+rec.Std	0.8165
+rec.Optimal_fieldtype	ENUM('1','2','3') NOT NULL
+DROP TABLE t1;
+#
+# End of 10.4 tests
+#