I am able to collect output data from a process, but I don't understand the
coordination of point and process-mark. In particular, the visible cursor in
a non-selected window visiting the buffer does not advance, even though point
is reported at correct locations when I access the variable. Selecting the
window moves point to an incorrect location.
(EDIT: in an earlier version of this question, I had some basic confusion about windows, frames, selection, and focus. I consulted the documentation here and edited this question to be coherent with emacs definitions.)
I'd be grateful for some explanations and corrections to the following MVE (minimal viable example). First, I start a process:
(start-process-shell-command
"foo-process"
"foo-buffer"
"python")
I open another window to watch what's going on: C-x3,
visit foo-buffer in that window C-xbfoo-buffer, and
select my programming window window again C-xo. The window
visiting foo-buffer is not selected at this time, but a shadowy cursor is
visible in the window.
I set up a couple of global variables for debugging and for collecting output and a function to report on the state:
(defvar my-python-buffer-data '())
(defvar my-python-latest-output "")
(defun report ()
(with-current-buffer "foo-buffer"
`((:point-min ,(point-min))
(:point ,(point))
(:point-max ,(point-max))
(:process-mark ,(process-mark (get-process "foo-process")))
(:buffer-data ,my-python-buffer-data)
(:latest-output ,my-python-latest-output))))
Before sending data to the buffer, I check the state by calling report:
(report)
((:point-min 1)
(:point 149)
(:point-max 149)
(:process-mark #<marker at 149 in foo-buffer>)
(:buffer-data nil)
(:latest-output ""))
Things seems consistent: the point and process marker are at the end of the buffer. I can also see that the shadowy cursor in the other window (which is not selected) is at the end of the buffer.
I now set up my custom "insertion filter," following the documentation in
section 38.9.2 of the elisp manual at this link address. I am using the
documented option of unconditionally setting point via goto-char at the end
of the filter function. I want point to be always at the end of the new output.
I collect data about point and the process mark as I go along, so I need a function to do that:
(defun collect-python-buffer-data (sigil)
(setq my-python-buffer-data
(cons
`(:sigil ,sigil :marker ,(process-mark proc) :point ,(point))
my-python-buffer-data)))
and here is my filter function, copy-pasted and modded from the doc:
(defun extracting-insertion-filter (proc string)
(setq my-python-buffer-data '())
(setq my-python-latest-output "")
(let ((pb (process-buffer proc)))
(when (buffer-live-p pb)
(with-current-buffer pb
(save-excursion
(collect-python-buffer-data 1)
(goto-char (process-mark proc))
(collect-python-buffer-data 2)
(insert string) ; advances point
(collect-python-buffer-data 3)
(set-marker (process-mark proc) (point))
(collect-python-buffer-data 4))
(goto-char (process-mark proc))
(collect-python-buffer-data 5)))
;; for reporting:
(setq my-python-buffer-data (reverse my-python-buffer-data))
(setq my-python-latest-output string)))
I now set the process filter for the process to my new function:
(set-process-filter
(get-process "foo-process")
#'extracting-insertion-filter)
and send some data to my process:
(process-send-string "foo-process" "420 / 3\n")
Now report:
(report)
((:point-min 1)
(:point 157)
(:point-max 157)
(:process-mark #<marker at 157 in foo-buffer>)
(:buffer-data ((:sigil 1 :marker #<marker at 157 in foo-buffer> :point 149)
(:sigil 2 :marker #<marker at 157 in foo-buffer> :point 149)
(:sigil 3 :marker #<marker at 157 in foo-buffer> :point 157)
(:sigil 4 :marker #<marker at 157 in foo-buffer> :point 157)
(:sigil 5 :marker #<marker at 157 in foo-buffer> :point 157)))
(:latest-output "140
>>> "))
Things look OK, here. I get my output, and point and process-mark are at the
end, where I want them.
However, the little shadowy cursor is at the wrong place in the non-selected window that shows my buffer. Before selecting that window (and spoiling the state), let me make sure that I can send more data over:
(process-send-string "foo-process" "42 / 3\n")
(report)
((:point-min 1)
(:point 164)
(:point-max 164)
(:process-mark #<marker at 164 in foo-buffer>)
(:buffer-data ((:sigil 1 :marker #<marker at 164 in foo-buffer> :point 149)
(:sigil 2 :marker #<marker at 164 in foo-buffer> :point 157)
(:sigil 3 :marker #<marker at 164 in foo-buffer> :point 164)
(:sigil 4 :marker #<marker at 164 in foo-buffer> :point 164)
(:sigil 5 :marker #<marker at 164 in foo-buffer> :point 164)))
(:latest-output "14
>>> "))
Everything is OK in the program, but the cursor in the non-selected window has
not moved. If I select that that window and un-select it, the party is spoiled,
i.e., point moved from 164 (where I want it) to 149, where it should
not have been after the initialization of the process buffer.
C-xoC-xo
(with-current-buffer "foo-buffer" (point))
149
Again, I'd be grateful for guidance on how to fix this. I tried the moving
option in the documentation, but the effect is the same.
