stream-advance-to-column not used

[Tomas Zellerin]

I define new subclass of fundamental-character-output-stream, and method sb-gray:stream-advance-to-column for it.

SBCL user manual says "This is intended for use by by pprint and format ~T." about the method (actually, this looks copied out as-is from gray streams specification). I call (format (make-instance 'tab-stream) "~8T") on the new class and I expect the method to be called; however, spaces are written instead.

In the sources I have at hand (1.3.3), formatter expands "~T" to sb-format::format-absolute-tab/format-relative-tab that call output-spaces; I can try to make a draft patch if it is agreed that this is indeed a bug and that the correct place to fix it is there; I am a bit lost in how the pretty printing related tab enqueuing, so I might have misdiagnosed the correct place or have a too simplistic view.

Observed on Windows with sbcl 1.3.3 as well as on Linux with sbcl 1.3.6, I can provide Linux uname and *features* at both if needed, but I do not think it is dependent on it.

Full test case:

(defclass tab-stream (sb-gray:fundamental-character-output-stream)
  ())

(defmethod sb-gray:stream-advance-to-column ((s tab-stream) col)
  (break "Do advance column") ;; <- I expect this break to be invoked
  t)

(defmethod sb-gray:stream-line-column ((s tab-stream))
  (format *standard-output* "Asked for column~%")
  0)

(defmethod sb-gray:stream-write-char ((s tab-stream) char)
  ;; Must be defined
  (format *standard-output* "Out: ~:c~%" char))

format (make-instance 'tab-stream) "~8T")

=>
Asked for column
Out: Space
Out: Space
Out: Space
Out: Space
Out: Space
Out: Space
Out: Space
Out: Space