MDEV-12011 sql_mode=ORACLE: cursor%ROWTYPE in variable declarations

Implementing cursor%ROWTYPE variables, according to the task description.

This patch includes a refactoring in how sp_instr_cpush and sp_instr_copen
work. This is needed to implement MDEV-10598 later easier, to allow variable
declarations go after cursor declarations (which is currently not allowed).

Before this patch, sp_instr_cpush worked as a Query_arena associated with
the cursor. sp_instr_copen::execute() switched to the sp_instr_cpush's
Query_arena when executing the cursor SELECT statement.

Now the Query_arena associated with the cursor is stored inside an instance
of a new class sp_lex_cursor (a LEX descendand) that contains the cursor SELECT
statement.

This simplifies the implementation, because:
- It's easier to follow the code when everything related to execution
  of the cursor SELECT statement is stored inside the same sp_lex_cursor
  object (rather than distributed between LEX and sp_instr_cpush).
- It's easier to link an sp_instr_cursor_copy_struct to
  sp_lex_cursor rather than to sp_instr_cpush.
- Also, it allows to perform sp_instr_cursor_copy_struct::exec_core()
  without having a pointer to sp_instr_cpush, using a pointer to sp_lex_cursor
  instead. This will be important for MDEV-10598, because sp_instr_cpush will
  happen *after* sp_instr_cursor_copy_struct.

After MDEV-10598 is done, this declaration:

DECLARE
  CURSOR cur IS SELECT * FROM t1;
  rec cur%ROWTYPE;
BEGIN
  OPEN cur;
  FETCH cur INTO rec;
  CLOSE cur;
END;

will generate about this code:

+-----+--------------------------+
| Pos | Instruction              |
+-----+--------------------------+
|   0 | cursor_copy_struct rec@0 | Points to sp_cursor_lex through m_lex_keeper
|   1 | set rec@0 NULL           |
|   2 | cpush cur@0              | Points to sp_cursor_lex through m_lex_keeper
|   3 | copen cur@0              | Points to sp_cursor_lex through m_cursor
|   4 | cfetch cur@0 rec@0       |
|   5 | cclose cur@0             |
|   6 | cpop 1                   |
+-----+--------------------------+

Notice, "cursor_copy_struct" and "set" will go before "cpush".
Instructions at positions 0, 2, 3 point to the same sp_cursor_lex instance.

1 files changed, 5 insertions, 5 deletions

diff --git a/sql/sp_rcontext.h b/sql/sp_rcontext.h
index 1c47b1caff0..98464518787 100644
--- a/sql/sp_rcontext.h
+++ b/sql/sp_rcontext.h
@@ -272,7 +272,7 @@ public:
   /// @return error flag.
   /// @retval false on success.
   /// @retval true on error.
-  bool push_cursor(THD *thd, sp_lex_keeper *lex_keeper, sp_instr_cpush *i);
+  bool push_cursor(THD *thd, sp_lex_keeper *lex_keeper);
 
   /// Pop and delete given number of sp_cursor instance from the cursor stack.
   ///
@@ -434,7 +434,7 @@ private:
 };
 
 public:
-  sp_cursor(THD *thd_arg, sp_lex_keeper *lex_keeper, sp_instr_cpush *i);
+  sp_cursor(THD *thd_arg, sp_lex_keeper *lex_keeper);
 
   virtual ~sp_cursor()
   { destroy(); }
@@ -443,6 +443,8 @@ public:
 
   int open(THD *thd);
 
+  int open_view_structure_only(THD *thd);
+
   int close(THD *thd);
 
   my_bool is_open()
@@ -459,14 +461,12 @@ public:
 
   int fetch(THD *, List<sp_variable> *vars);
 
-  sp_instr_cpush *get_instr()
-  { return m_i; }
+  bool export_structure(THD *thd, Row_definition_list *list);
 
 private:
   Select_fetch_into_spvars result;
   sp_lex_keeper *m_lex_keeper;
   Server_side_cursor *server_side_cursor;
-  sp_instr_cpush *m_i;     // My push instruction
   ulonglong m_fetch_count; // Number of FETCH commands since last OPEN
   ulonglong m_row_count;   // Number of successful FETCH since last OPEN
   bool m_found;            // If last FETCH fetched a row