pprint directive in format isn't recognized when called via write-object

[shirok]

gosh> (define-class <x> () ())
<x>
gosh> (define (p port) (format port "abc ~:w def" (make-list 100 'a)))
p
gosh> (p (current-output-port))
abc (a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
     a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a
     a a a a a a a a a a a a a a a a a a a a a a a a a a) def#<undef>
gosh> (define-method write-object ((x <x>) port) (p port))
#:|write-object((x <x>) port).642|
gosh> (make <x>)
abc (a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a ...) def

[shirok]

The object is passed to write, which determines whether the content is to be handled with %pretty-print or with the internal writer, in pprintable_p(). Currently it returns false for <object>, meaning it is handled internally, not passed to %pretty-print. It's because %pretty-print delegates printing of <object> to the intenral writer, so passing <object> to %pretty-print causes infinite loop.