Please refer to xtra/pgscript/doc/developers.html for the pgScript developer
documentation.

parser.sh must be called for regenerating Flex and Bison source files because it
does some more processing than just executing Bison and Flex: it replaces some
headers and add other ones.

Please use Flex 2.5.33 otherwise the pgadmin/include/pgscript/FlexLexer.h file
will not be valid. If you use a different version from 2.5.33 you need to copy FlexLexer.h that comes along with your Flex distribution to
pgadmin/include/pgscript.