#define PG_ENCODING_BE_LAST PG_ISO_8859_8
#define PG_ENCODING_FE_LAST PG_WIN1256

but the last client encoding in the enum list is actually PG_GB18030 and
it seems that

#define PG_ENCODING_IS_CLIEN_ONLY(_enc) \
                (((_enc) > PG_ENCODING_BE_LAST && (_enc) <= PG_ENCODING_FE_LAST)

can never be true.

I think the define should read
#define PG_ENCODING_FE_LAST PG_GB18030

On the other hand, perhaps no-one cares, because
PG_ENCODING_IS_CLIEN_ONLY is never used.

--
Oliver Elphick                                Oliver.Elphick@lfix.co.uk