GIS data types are declared as (non-reserved) keywords in lex.h:

  { "GEOMETRY",                SYM(GEOMETRY_SYM)},

  { "GEOMETRYCOLLECTION",SYM(GEOMETRYCOLLECTION)},

  { "LINESTRING",      SYM(LINESTRING)},

  { "MULTILINESTRING", SYM(MULTILINESTRING)},

  { "MULTIPOINT",      SYM(MULTIPOINT)},

  { "MULTIPOLYGON",    SYM(MULTIPOLYGON)},

  { "POINT",           SYM(POINT_SYM)},

  { "POLYGON",         SYM(POLYGON)},

There is an sql_yacc.yy rule to parse GIS data types:

spatial_type:

          GEOMETRY_SYM       { $$= GEOM_TYPE(&type_handler_geometry); }

        | GEOMETRYCOLLECTION { $$= GEOM_TYPE(&type_handler_geometrycollection);

        | POINT_SYM          { $$= GEOM_TYPE(&type_handler_point); }

        | MULTIPOINT         { $$= GEOM_TYPE(&type_handler_multipoint); }

        | LINESTRING         { $$= GEOM_TYPE(&type_handler_linestring); }

        | MULTILINESTRING    { $$= GEOM_TYPE(&type_handler_multilinestring); }

        | POLYGON            { $$= GEOM_TYPE(&type_handler_polygon); }

        | MULTIPOLYGON       { $$= GEOM_TYPE(&type_handler_multipolygon); }

        ;

There is also another sql_yacc.yy rule to create GIS contructor functions:

        | GEOMETRYCOLLECTION '(' expr_list ')'

          {

            $$= GEOM_NEW(thd, Item_func_geometrycollection(thd, *$3));

          }

        | LINESTRING '(' expr_list ')'

          {

            $$= GEOM_NEW(thd, Item_func_linestring(thd, *$3));

          }

        | MULTILINESTRING '(' expr_list ')'

          {

            $$= GEOM_NEW(thd, Item_func_multilinestring(thd, *$3));

          }

        | MULTIPOINT '(' expr_list ')'

          {

            $$= GEOM_NEW(thd, Item_func_multipoint(thd, *$3));

          }

        | MULTIPOLYGON '(' expr_list ')'

          {

            $$= GEOM_NEW(thd, Item_func_multipolygon(thd, *$3));

          }

        | POINT_SYM '(' expr ',' expr ')'

          {

            $$= GEOM_NEW(thd, Item_func_point(thd, $3, $5));

          }

        | POLYGON '(' expr_list ')'

          {

            $$= GEOM_NEW(thd, Item_func_polygon(thd, *$3));

          }

Under terms of this task we'll make GIS data types more plugable:

• remove the above keyword definitions and grammar rules
• add a new method in Type_handler:

  static handler_by_name(const LEX_CSTRING &name);

• add a new method in Type_handler:

  virtual Item *make_constructor_item(THD *thd, List<Item> *args) const

  {

  return NULL;

  }

• The grammar to parse a GIS data type will turn into:

  | IDENT_sys float_options srid_option

  {

  const Type_handler *h;

  if (!(h= Type_handler::handler_by_name_or_error($1)))

  MYSQL_YYABORT;

  $$.set(h, $2);

  Lex->charset= &my_charset_bin;

  }

  ;

• The grammar to parse GIS contructor functions will be removed, and a new code path will be added into the rule function_call_generic instead, with approximately this diff:

  - builder= find_native_function_builder(thd, &$1);

  - if (builder)

  + if ((h= Type_handler::handler_by_name($1)) &&

  + (item= h->make_constructor_item(thd, $4)))

  + {

  + // Found a constructor with a proper argument count

  + }

  + else if ((builder= find_native_function_builder(thd, &$1))

These changes will help to add pluggable data types and new built-in data types in a simple way, without changes in sql_yacc.yy.