MDEV-11245 Move prepare_create_field and sp_prepare_create_field() as methods to Column_definition

Some upcoming tasks, e.g.:
- MDEV-10577 sql_mode=ORACLE: %TYPE in variable declarations
- MDEV-10914 ROW data type for stored routine variables

will need to reuse the code implemented in prepare_create_field(),
sp_prepare_create_field(), prepare_blob_field().

Before reusing this code, it's a good idea to move these global functions
as methods to Column_definition.

This patch:
- actually moves prepare_create_field(), sp_prepare_create_field(),
  prepare_blob_field() as methods to Column_definition
- makes sp_prepare_create_field() call prepare_create_field() at the end,
  to avoid duplicate code in MDEV-10577 and MDEV-10914.
- changes the return data type for prepare_create_field() from int to bool,
  to make it consistent with all other functions returning "ok" or "error".
- moves the implementation sp_head::fill_field_definition() from sp_head.cc
  to sp_head.h, as it now uses globally visible Column_definition methods,
  and is very simple, so inlining is now possible.
- removes the unused "LEX*" argument from sp_head::fill_field_definition()

1 files changed, 7 insertions, 0 deletions

diff --git a/sql/field.h b/sql/field.h
index b55cc9a0c58..36ac7f5f528 100644
--- a/sql/field.h
+++ b/sql/field.h
@@ -3872,6 +3872,13 @@ public:
     set_if_smaller(length, MAX_FIELD_WIDTH - 1);
     DBUG_RETURN(false);
   }
+
+  bool prepare_blob_field(THD *thd);
+
+  bool sp_prepare_create_field(THD *thd, MEM_ROOT *mem_root);
+
+  bool prepare_create_field(uint *blob_columns, longlong table_flags);
+
   bool check(THD *thd);
 
   bool stored_in_db() const { return !vcol_info || vcol_info->stored_in_db; }