A cleanup patch for MDEV-12011 sql_mode=ORACLE: cursor%ROWTYPE in variable declarations

Addressing Monty's review suggestions

sql/field.h

@@ -3987,16 +3987,6 @@ public:
 };
 
 
-class Cursor_rowtype: public Sql_alloc
-{
-public:
-  uint m_cursor;
-  Cursor_rowtype(uint cursor)
-   :m_cursor(cursor)
-  { }
-};
-
-
 /**
   This class is used during a stored routine or a trigger execution,
   at sp_rcontext::create() time.
@@ -4020,20 +4010,20 @@ class Spvar_definition: public Column_definition
 {
   class Qualified_column_ident *m_column_type_ref; // for %TYPE
   class Table_ident *m_table_rowtype_ref;          // for table%ROWTYPE
-  class Cursor_rowtype *m_cursor_rowtype_ref;      // for cursor%ROWTYPE
+  bool m_cursor_rowtype_ref;                       // for cursor%ROWTYPE
   Row_definition_list *m_row_field_definitions;    // for ROW
 public:
   Spvar_definition()
    :m_column_type_ref(NULL),
     m_table_rowtype_ref(NULL),
-    m_cursor_rowtype_ref(NULL),
+    m_cursor_rowtype_ref(false),
     m_row_field_definitions(NULL)
   { }
   Spvar_definition(THD *thd, Field *field)
    :Column_definition(thd, field, NULL),
     m_column_type_ref(NULL),
     m_table_rowtype_ref(NULL),
-    m_cursor_rowtype_ref(NULL),
+    m_cursor_rowtype_ref(false),
     m_row_field_definitions(NULL)
   { }
   const Type_handler *type_handler() const
@@ -4044,7 +4034,7 @@ public:
   }
   bool is_column_type_ref() const { return m_column_type_ref != 0; }
   bool is_table_rowtype_ref() const { return m_table_rowtype_ref != 0; }
-  bool is_cursor_rowtype_ref() const { return m_cursor_rowtype_ref != NULL; }
+  bool is_cursor_rowtype_ref() const { return m_cursor_rowtype_ref; }
   class Qualified_column_ident *column_type_ref() const
   {
     return m_column_type_ref;
@@ -4062,11 +4052,7 @@ public:
   {
     m_table_rowtype_ref= ref;
   }
-  class Cursor_rowtype *cursor_rowtype_ref() const
-  {
-    return m_cursor_rowtype_ref;
-  }
-  void set_cursor_rowtype_ref(class Cursor_rowtype *ref)
+  void set_cursor_rowtype_ref(bool ref)
   {
     m_cursor_rowtype_ref= ref;
   }

sql/sp_head.cc

@@ -3183,7 +3183,6 @@ int sp_lex_keeper::cursor_reset_lex_and_exec_core(THD *thd, uint *nextp,
   */
   thd->stmt_arena= m_lex->query_arena();
   int res= reset_lex_and_exec_core(thd, nextp, open_tables, instr);
-  if (thd->stmt_arena->free_list)
   cleanup_items(thd->stmt_arena->free_list);
   thd->stmt_arena= old_arena;
   return res;
@@ -4170,10 +4169,18 @@ sp_instr_cfetch::print(String *str)
   sp_instr_cursor_copy_struct class functions
 */
 
+/**
+  This methods processes cursor %ROWTYPE declarations, e.g.:
+    CURSOR cur IS SELECT * FROM t1;
+    rec cur%ROWTYPE;
+  and does the following:
+  - opens the cursor without copying data (materialization).
+  - copies the cursor structure to the associated %ROWTYPE variable.
+*/
 int
 sp_instr_cursor_copy_struct::exec_core(THD *thd, uint *nextp)
 {
-  DBUG_ENTER("sp_instr_cusrot_copy_struct::exec_core");
+  DBUG_ENTER("sp_instr_cursor_copy_struct::exec_core");
   int ret= 0;
   Item_field_row *row= (Item_field_row*) thd->spcont->get_item(m_var);
   DBUG_ASSERT(row->type_handler() == &type_handler_row);
@@ -4188,6 +4195,7 @@ sp_instr_cursor_copy_struct::exec_core(THD *thd, uint *nextp)
   if (!row->arguments())
   {
     sp_cursor tmp(thd, &m_lex_keeper);
+    // Open the cursor without copying data
     if (!(ret= tmp.open_view_structure_only(thd)))
     {
       Row_definition_list defs;

sql/sp_rcontext.cc

@@ -743,11 +743,17 @@ int sp_cursor::open(THD *thd)
 }
 
 
+/**
+  Open the cursor, but do not copy data.
+  This method is used to fetch the cursor structure
+  to cursor%ROWTYPE routine variables.
+  Data copying is suppressed by setting thd->lex->limit_rows_examined to 0.
+*/
 int sp_cursor::open_view_structure_only(THD *thd)
 {
   int res;
   int thd_no_errors_save= thd->no_errors;
-  Item *limit_rows_examined= thd->lex->limit_rows_examined;
+  Item *limit_rows_examined= thd->lex->limit_rows_examined; // No data copying
   if (!(thd->lex->limit_rows_examined= new (thd->mem_root) Item_uint(thd, 0)))
     return -1;
   thd->no_errors= true; // Suppress ER_QUERY_EXCEEDED_ROWS_EXAMINED_LIMIT

sql/sql_lex.cc

@@ -5303,10 +5303,7 @@ LEX::sp_variable_declarations_rowtype_finalize(THD *thd, int nvars,
 
     if (pcursor)
     {
-      Cursor_rowtype *ref;
-      if (!(ref= new (thd->mem_root) Cursor_rowtype(coffp)))
-        return true;
-      spvar->field_def.set_cursor_rowtype_ref(ref);
+      spvar->field_def.set_cursor_rowtype_ref(true);
       sp_instr_cursor_copy_struct *instr=
         new (thd->mem_root) sp_instr_cursor_copy_struct(sphead->instructions(),
                                                         spcont, pcursor->lex(),
@@ -5435,10 +5432,7 @@ LEX::sp_add_for_loop_cursor_variable(THD *thd,
   sphead->fill_spvar_definition(thd, &spvar->field_def, spvar->name.str);
   spvar->default_value= new (thd->mem_root) Item_null(thd);
 
-  Cursor_rowtype *ref;
-  if (!(ref= new (thd->mem_root) Cursor_rowtype(coffset)))
-    return NULL;
-  spvar->field_def.set_cursor_rowtype_ref(ref);
+  spvar->field_def.set_cursor_rowtype_ref(true);
 
   if (sphead->add_for_loop_open_cursor(thd, spcont, spvar, pcursor, coffset,
                                        param_lex, parameters))