A cleanup for MDEV-10914 ROW data type for stored routine variables

Changing datatypes for:
- Item_spvar_args::m_table
- sp_rcontext::m_var_table
- return value of create_virtual_tmp_table()
from TABLE* to Virtual_tmp_table*

Advantages:
- Stricter data type control
- Removing the duplicate code (a loop with free_blobs)
  from destructors ~sp_rcontext() and ~Item_spvar_args(),
  using "delete m_(var_)table" in both instead.
- Using Virtual_tmp_table::delete makes the code call Field::delete,
  which calls TRASH() for the freed fields,
  which is good for valgrind test runs.

sql/item.h

@@ -89,6 +89,7 @@ class ValueBuffer: public Value
 
 const char *dbug_print_item(Item *item);
 
+class Virtual_tmp_table;
 class sp_head;
 class Protocol;
 struct TABLE_LIST;
@@ -2093,16 +2094,12 @@ class Item_args
 
 class Item_spvar_args: public Item_args
 {
-  TABLE *m_table;
+  Virtual_tmp_table *m_table;
 public:
   Item_spvar_args():Item_args(), m_table(NULL) { }
   ~Item_spvar_args();
   bool row_create_items(THD *thd, List<Spvar_definition> *list);
-  Field *get_row_field(uint i) const
-  {
-    DBUG_ASSERT(m_table);
-    return m_table->field[i];
-  }
+  Field *get_row_field(uint i) const;
 };
 
 

sql/sp_rcontext.cc

@@ -51,9 +51,7 @@ sp_rcontext::sp_rcontext(const sp_pcontext *root_parsing_ctx,
 
 sp_rcontext::~sp_rcontext()
 {
-  if (m_var_table)
-    free_blobs(m_var_table);
-
+  delete m_var_table;
   // Leave m_handlers, m_handler_call_stack, m_var_items, m_cstack
   // and m_case_expr_holders untouched.
   // They are allocated in mem roots and will be freed accordingly.
@@ -375,10 +373,16 @@ bool Item_spvar_args::row_create_items(THD *thd, List<Spvar_definition> *list)
 }
 
 
+Field *Item_spvar_args::get_row_field(uint i) const
+{
+  DBUG_ASSERT(m_table);
+  return m_table->field[i];
+}
+
+
 Item_spvar_args::~Item_spvar_args()
 {
-  if (m_table)
-    free_blobs(m_table);
+  delete m_table;
 }
 
 

sql/sp_rcontext.h

@@ -34,6 +34,7 @@ class sp_instr_cpush;
 class Query_arena;
 class sp_head;
 class Item_cache;
+class Virtual_tmp_table;
 
 
 /*
@@ -365,7 +366,7 @@ class sp_rcontext : public Sql_alloc
   const sp_pcontext *m_root_parsing_ctx;
 
   /// Virtual table for storing SP-variables.
-  TABLE *m_var_table;
+  Virtual_tmp_table *m_var_table;
 
   /// Collection of Item_field proxies, each of them points to the
   /// corresponding field in m_var_table.

sql/sql_select.h

@@ -2013,7 +2013,7 @@ Field *create_tmp_field(THD *thd, TABLE *table,Item *item, Item::Type type,
 class Virtual_tmp_table: public TABLE
 {
   /**
-    Destruct collected fields. This method is called on errors only,
+    Destruct collected fields. This method can be called on errors,
     when we could not make the virtual temporary table completely,
     e.g. when some of the fields could not be created or added.
 
@@ -2024,7 +2024,10 @@ class Virtual_tmp_table: public TABLE
   void destruct_fields()
   {
     for (uint i= 0; i < s->fields; i++)
+    {
+      field[i]->free();
       delete field[i];  // to invoke the field destructor
+    }
     s->fields= 0;       // safety
   }
 
@@ -2144,7 +2147,7 @@ class Virtual_tmp_table: public TABLE
     TABLE object ready for read and write in case of success
 */
 
-inline TABLE *
+inline Virtual_tmp_table *
 create_virtual_tmp_table(THD *thd, List<Spvar_definition> &field_list)
 {
   Virtual_tmp_table *table;