MDEV-15107 Add virtual Field::sp_prepare_and_store_item(), make sp_rcontext symmetric for scalar and ROW

After MDEV-14212, the Virtual_tmp_table instance that stores a ROW
variable elements is accessible from the underlying Field_row
(rather than Item_field_row).

This patch makes some further changes by moving the code from
sp_instr_xxx, sp_rcontext, Item_xxx to Virtual_tmp_table and Field_xxx.

The data type specific code (scalar vs ROW) now resides in
a new virtual method Field_xxx::sp_prepare_and_store_item().
The the code in sp_rcontext::set_variable() and sp_eval_expr()
is now symmetric for scalar and ROW values.
The code in sp_rcontext::set_variable_row_field(), sp_rcontext::set_variable_row_field(), sp_rcontext::set_variable_row()
is now symmetric for ROW elements (i.e. scalar and ROW elements inside a ROW).

Rationale:

Prepare the code to implement these tasks soon easier:

- MDEV-12252 ROW data type for stored function return values
- MDEV-12307 ROW data type for built-in function return values
- MDEV-6121 Data type: Array
- MDEV-10593 sql_mode=ORACLE: TYPE .. AS OBJECT: basic functionality
- ROW with ROW fields (no MDEV yet)

Details:

1. Moving the code in sp_eval_expr() responsible to backup/restore
   thd->count_cuted_fields, thd->abort_on_warning,
   thd->transaction.stmt.modified_non_trans_table
   into a new helper class Sp_eval_expr_state, to reuse it easier.
   Fixing sp_eval_expr() to use this new class.

2. Moving sp_eval_expr() and sp_prepare_func_item() from public functions
   to methods in THD, so they can be reused in *.cc files easier without
   a need to include "sp_head.h".

   Splitting sp_prepare_func_item() into two parts.
   Adding a new function sp_fix_func_item(), which fixes
   the underlying items, but does not do check_cols() for them.
   Reusing sp_fix_func_item() in Field_row::sp_prepare_and_store_item().

3. Moving the code to find ROW fields by name from Item to Virtual_tmp_table

   Moving the code searching for ROW fields by their names
   from Item_field_row::element_index_by_name() to a new method
   Item_field_row to Virtual_tmp_table::sp_find_field_by_name().

   Adding wrapper methods sp_rcontext::find_row_field_by_name() and
   find_row_field_by_name_or_error(), to search for a ROW variable
   fields by the variable offset and its field name.

   Changing Item_splocal_row_field_by_name::fix_fields() to do
   use sp_rcontext::find_row_field_by_name_or_error().
   Removing virtual Item::element_index_by_name().

4. Splitting sp_rcontext::set_variable()

   Adding a new virtual method Field::sp_prepare_and_store_item().
   Spliting the two branches of the code in sp_rcontext::set_variable()
   into two virtual implementations of Field::sp_prepare_and_store_item(),
   (for Field and for Field_row).

   Moving the former part of sp_rcontext::set_variable() with the loop
   doing set_null() for all ROW fields into a new method
   Virtual_tmp_table::set_all_fields_to_null() and using it in
   Field_row::sp_prepare_and_store_item().

   Moving the former part of sp_rcontext::set_variable() with the loop
   doing set_variable_row_field() into a new method
   Virtual_tmp_table::set_all_fields_from_item() and using it in
   Field_row::sp_prepare_and_store_item().
   The loop in the new method now uses sp_prepare_and_store_item()
   instead of set_variable_row_field(), because saving/restoring
   THD flags is now done on the upper level. No needs to save/restore
   on every iteration.

5. Fixing sp_eval_expr() to simply do two things:
   - backup/restore THD flags
   - call result_field->sp_prepare_and_store_item()
   So now sp_eval_expr() can be used for both scalar and ROW variables.
   Reusing it in sp_rcontext::set_variable*().

6. Moving the loop in sp_rcontext::set_variable_row() into a
   new method Virtual_tmp_table::sp_set_all_fields_from_item_list().

   Changing the loop body to call field->sp_prepare_and_store_item()
   instead of doing set_variable_row_field(). This removes
   saving/restoring of the THD flags from every interation.
   Instead, adding the code to save/restore the flags around
   the entire loop in set_variable_row(), using Sp_eval_expr_state.
   So now saving/restoring is done only once for the entire ROW
   (a slight performance improvement).

7. Removing the code in sp_instr_set::exec_core() that sets
   a variable to NULL if the value evaluation failed.
   sp_rcontext::set_variable() now makes sure to reset
   the variable properly by effectively calling sp_eval_expr(),
   which calls virtual Field::sp_prepare_and_store_item().

   Removing the similar code from sp_instr_set_row_field::exec_core()
   and sp_instr_set_row_field_by_name::exec_core().

   Removing the method sp_rcontext::set_variable_row_field_to_null(),
   as it's not used any more.

8. Removing the call for sp_prepare_func_item() from
   sp_rcontext::set_variable_row_field(), as it was duplicate:
   it was done inside sp_eval_expr(). Now it's done inside
   virtual Field::sp_prepare_and_store_item().

9. Moving the code from sp_instr_set_row_field_by_name::exec_core()
   into sp_rcontext::set_variable_row_field_by_name(), for symmetry
   with other sp_instr_set*::exec_core()/sp_rcontext::set_variable*() pairs.
   Now sp_instr_set_row_field_by_name::exec_core() calls
   sp_rcontext::set_variable_row_field_by_name().

10. Misc:
   - Adding a helper private method sp_rcontext::virtual_tmp_table_for_row(),
     reusing it in a new sp_rcontext methods.
   - Removing Item_field_row::get_row_field(), as it's not used any more.
   - Removing the "Item *result_item" from sp_eval_expr(),
     as it's not needed any more.

1 files changed, 45 insertions, 90 deletions

diff --git a/sql/sp_rcontext.cc b/sql/sp_rcontext.cc
index 62b5439d84d..43d033ad83e 100644
--- a/sql/sp_rcontext.cc
+++ b/sql/sp_rcontext.cc
@@ -388,22 +388,13 @@ bool Item_field_row::row_create_items(THD *thd, List<Spvar_definition> *list)
 }
 
 
-Field *Item_field_row::get_row_field(uint i) const
-{
-  DBUG_ASSERT(field);
-  Virtual_tmp_table **ptable= field->virtual_tmp_table_addr();
-  DBUG_ASSERT(ptable);
-  return ptable[0]->field[i];
-}
-
-
 bool sp_rcontext::set_return_value(THD *thd, Item **return_value_item)
 {
   DBUG_ASSERT(m_return_value_fld);
 
   m_return_value_set = true;
 
-  return sp_eval_expr(thd, NULL, m_return_value_fld, return_value_item);
+  return thd->sp_eval_expr(m_return_value_fld, return_value_item);
 }
 
 
@@ -612,84 +603,31 @@ uint sp_rcontext::exit_handler(Diagnostics_area *da)
 
 int sp_rcontext::set_variable(THD *thd, uint idx, Item **value)
 {
-  Field *field= m_var_table->field[idx];
-  if (!value)
-  {
-    field->set_null();
-    return 0;
-  }
-  Item *dst= m_var_items[idx];
-
-  if (dst->cmp_type() != ROW_RESULT)
-    return sp_eval_expr(thd, dst, m_var_table->field[idx], value);
-
-  DBUG_ASSERT(dst->type() == Item::FIELD_ITEM);
-  if (value[0]->type() == Item::NULL_ITEM)
-  {
-    /*
-      We're in a auto-generated sp_inst_set, to assign
-      the explicit default NULL value to a ROW variable.
-    */
-    for (uint i= 0; i < dst->cols(); i++)
-    {
-      Item_field_row *item_field_row= (Item_field_row*) dst;
-      item_field_row->get_row_field(i)->set_null();
-    }
-    return false;
-  }
-
-  /**
-    - In case if we're assigning a ROW variable from another ROW variable,
-      value[0] points to Item_splocal. sp_prepare_func_item() will return the
-      fixed underlying Item_field_spvar with ROW members in its aguments().
-    - In case if we're assigning from a ROW() value, src and value[0] will
-      point to the same Item_row.
-  */
-  Item *src;
-  if (!(src= sp_prepare_func_item(thd, value, dst->cols())) ||
-      src->cmp_type() != ROW_RESULT)
-  {
-    my_error(ER_OPERAND_COLUMNS, MYF(0), dst->cols());
-    return true;
-  }
-  DBUG_ASSERT(dst->cols() == src->cols());
-  for (uint i= 0; i < src->cols(); i++)
-    set_variable_row_field(thd, idx, i, src->addr(i));
-  return false;
-}
-
-
-void sp_rcontext::set_variable_row_field_to_null(THD *thd,
-                                                 uint var_idx,
-                                                 uint field_idx)
-{
-  Item *dst= get_item(var_idx);
-  DBUG_ASSERT(dst->type() == Item::FIELD_ITEM);
-  DBUG_ASSERT(dst->cmp_type() == ROW_RESULT);
-  Item_field_row *item_field_row= (Item_field_row*) dst;
-  item_field_row->get_row_field(field_idx)->set_null();
+  DBUG_ENTER("sp_rcontext::set_variable");
+  DBUG_ASSERT(value);
+  DBUG_RETURN(thd->sp_eval_expr(m_var_table->field[idx], value));
 }
 
 
 int sp_rcontext::set_variable_row_field(THD *thd, uint var_idx, uint field_idx,
                                         Item **value)
 {
+  DBUG_ENTER("sp_rcontext::set_variable_row_field");
   DBUG_ASSERT(value);
-  Item *dst= get_item(var_idx);
-  DBUG_ASSERT(dst->type() == Item::FIELD_ITEM);
-  DBUG_ASSERT(dst->cmp_type() == ROW_RESULT);
-  Item_field_row *item_field_row= (Item_field_row*) dst;
+  Virtual_tmp_table *vtable= virtual_tmp_table_for_row(var_idx);
+  DBUG_RETURN(thd->sp_eval_expr(vtable->field[field_idx], value));
+}
 
-  Item *expr_item= sp_prepare_func_item(thd, value);
-  if (!expr_item)
-  {
-    DBUG_ASSERT(thd->is_error());
-    return true;
-  }
-  return sp_eval_expr(thd,
-                      item_field_row->arguments()[field_idx],
-                      item_field_row->get_row_field(field_idx),
-                      value);
+
+int sp_rcontext::set_variable_row_field_by_name(THD *thd, uint var_idx,
+                                                const LEX_CSTRING &field_name,
+                                                Item **value)
+{
+  DBUG_ENTER("sp_rcontext::set_variable_row_field_by_name");
+  uint field_idx;
+  if (find_row_field_by_name_or_error(&field_idx, var_idx, field_name))
+    DBUG_RETURN(1);
+  DBUG_RETURN(set_variable_row_field(thd, var_idx, field_idx, value));
 }
 
 
@@ -697,15 +635,32 @@ int sp_rcontext::set_variable_row(THD *thd, uint var_idx, List<Item> &items)
 {
   DBUG_ENTER("sp_rcontext::set_variable_row");
   DBUG_ASSERT(get_item(var_idx)->cols() == items.elements);
-  List_iterator<Item> it(items);
-  Item *item;
-  for (uint i= 0 ; (item= it++) ; i++)
-  {
-    int rc;
-    if ((rc= set_variable_row_field(thd, var_idx, i, &item)))
-      DBUG_RETURN(rc);
-  }
-  DBUG_RETURN(0);
+  Virtual_tmp_table *vtable= virtual_tmp_table_for_row(var_idx);
+  Sp_eval_expr_state state(thd);
+  DBUG_RETURN(vtable->sp_set_all_fields_from_item_list(thd, items));
+}
+
+
+Virtual_tmp_table *sp_rcontext::virtual_tmp_table_for_row(uint var_idx)
+{
+  DBUG_ASSERT(get_item(var_idx)->type() == Item::FIELD_ITEM);
+  DBUG_ASSERT(get_item(var_idx)->cmp_type() == ROW_RESULT);
+  Field *field= m_var_table->field[var_idx];
+  Virtual_tmp_table **ptable= field->virtual_tmp_table_addr();
+  DBUG_ASSERT(ptable);
+  DBUG_ASSERT(ptable[0]);
+  return ptable[0];
+}
+
+
+bool sp_rcontext::find_row_field_by_name_or_error(uint *field_idx,
+                                                  uint var_idx,
+                                                  const LEX_CSTRING &field_name)
+{
+  Virtual_tmp_table *vtable= virtual_tmp_table_for_row(var_idx);
+  Field *row= m_var_table->field[var_idx];
+  return vtable->sp_find_field_by_name_or_error(field_idx,
+                                                row->field_name, field_name);
 }
 
 
@@ -728,7 +683,7 @@ Item_cache *sp_rcontext::create_case_expr_holder(THD *thd,
 bool sp_rcontext::set_case_expr(THD *thd, int case_expr_id,
                                 Item **case_expr_item_ptr)
 {
-  Item *case_expr_item= sp_prepare_func_item(thd, case_expr_item_ptr);
+  Item *case_expr_item= thd->sp_prepare_func_item(case_expr_item_ptr);
   if (!case_expr_item)
     return true;