Bug #31155 gis types in union'd select cause crash.

We use get_geometry_type() call to decide the exact type
of a geometry field to be created (POINT, POLYGON etc)
Though this function was only implemented for few items.
In the bug's case we need to call this function for the
Item_sum instance, where it was not implemented, what is
the reason of the crash.
Fixed by implementing virtual Item::get_geometry_type(),
so it can be called for any Item.

sql/item.cc

@@ -4364,11 +4364,8 @@ Field *Item::tmp_table_field_from_field_type(TABLE *table)
                           collation.collation);
     break;					// Blob handled outside of case
   case MYSQL_TYPE_GEOMETRY:
-    return new Field_geom(max_length, maybe_null, name, table,
-                          (Field::geometry_type)
-                          ((type() == Item::TYPE_HOLDER) ?
-                           ((Item_type_holder *)this)->get_geometry_type() :
-                           ((Item_geometry_func *)this)->get_geometry_type()));
+    return new Field_geom(max_length, maybe_null,
+                          name, table, get_geometry_type());
   }
 }
 
@@ -6489,9 +6486,7 @@ Item_type_holder::Item_type_holder(THD *thd, Item *item)
     decimals= 0;
   prev_decimal_int_part= item->decimal_int_part();
   if (item->field_type() == MYSQL_TYPE_GEOMETRY)
-    geometry_type= (item->type() == Item::FIELD_ITEM) ?
-      ((Item_field *)item)->get_geometry_type() :
-      (Field::geometry_type)((Item_geometry_func *)item)->get_geometry_type();
+    geometry_type= item->get_geometry_type();
 }
 
 

sql/item.h

@@ -870,6 +870,8 @@ public:
   */
   virtual bool result_as_longlong() { return FALSE; }
   bool is_datetime();
+  virtual Field::geometry_type get_geometry_type() const
+    { return Field::GEOM_GEOMETRY; };
 };
 
 
@@ -1335,7 +1337,7 @@ public:
   int fix_outer_field(THD *thd, Field **field, Item **reference);
   virtual Item *update_value_transformer(byte *select_arg);
   void print(String *str);
-  Field::geometry_type get_geometry_type()
+  Field::geometry_type get_geometry_type() const
   {
     DBUG_ASSERT(field_type() == MYSQL_TYPE_GEOMETRY);
     return field->get_geometry_type();
@@ -2637,7 +2639,7 @@ public:
   Field *make_field_by_type(TABLE *table);
   static uint32 display_length(Item *item);
   static enum_field_types get_real_type(Item *);
-  Field::geometry_type get_geometry_type() { return geometry_type; };
+  Field::geometry_type get_geometry_type() const { return geometry_type; };
 };
 
 

sql/item_geofunc.cc

@@ -27,7 +27,7 @@
 Field *Item_geometry_func::tmp_table_field(TABLE *t_arg)
 {
   return new Field_geom(max_length, maybe_null, name, t_arg,
-                        (Field::geometry_type) get_geometry_type());
+                        get_geometry_type());
 }
 
 void Item_geometry_func::fix_length_and_dec()
@@ -38,10 +38,6 @@ void Item_geometry_func::fix_length_and_dec()
   maybe_null= 1;
 }
 
-int Item_geometry_func::get_geometry_type() const
-{
-  return (int)Field::GEOM_GEOMETRY;
-}
 
 String *Item_func_geometry_from_text::val_str(String *str)
 {
@@ -160,9 +156,9 @@ String *Item_func_geometry_type::val_str(String *str)
 }
 
 
-int Item_func_envelope::get_geometry_type() const
+Field::geometry_type Item_func_envelope::get_geometry_type() const
 {
-  return (int) Field::GEOM_POLYGON;
+  return Field::GEOM_POLYGON;
 }
 
 
@@ -190,9 +186,9 @@ String *Item_func_envelope::val_str(String *str)
 }
 
 
-int Item_func_centroid::get_geometry_type() const
+Field::geometry_type Item_func_centroid::get_geometry_type() const
 {
-  return (int) Field::GEOM_POINT;
+  return Field::GEOM_POINT;
 }
 
 
@@ -330,9 +326,9 @@ err:
 */
 
 
-int Item_func_point::get_geometry_type() const
+Field::geometry_type Item_func_point::get_geometry_type() const
 {
-  return (int) Field::GEOM_POINT;
+  return Field::GEOM_POINT;
 }
 
 

sql/item_geofunc.h

@@ -33,7 +33,6 @@ public:
   void fix_length_and_dec();
   enum_field_types field_type() const  { return MYSQL_TYPE_GEOMETRY; }
   Field *tmp_table_field(TABLE *t_arg);
-  virtual int get_geometry_type() const;
   bool is_null() { (void) val_int(); return null_value; }
 };
 
@@ -92,7 +91,7 @@ public:
   Item_func_centroid(Item *a): Item_geometry_func(a) {}
   const char *func_name() const { return "centroid"; }
   String *val_str(String *);
-  int get_geometry_type() const;
+  Field::geometry_type get_geometry_type() const;
 };
 
 class Item_func_envelope: public Item_geometry_func
@@ -101,7 +100,7 @@ public:
   Item_func_envelope(Item *a): Item_geometry_func(a) {}
   const char *func_name() const { return "envelope"; }
   String *val_str(String *);
-  int get_geometry_type() const;
+  Field::geometry_type get_geometry_type() const;
 };
 
 class Item_func_point: public Item_geometry_func
@@ -111,7 +110,7 @@ public:
   Item_func_point(Item *a, Item *b, Item *srid): Item_geometry_func(a, b, srid) {}
   const char *func_name() const { return "point"; }
   String *val_str(String *);
-  int get_geometry_type() const;
+  Field::geometry_type get_geometry_type() const;
 };
 
 class Item_func_spatial_decomp: public Item_geometry_func