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Re: call-process and incremental display of output

From: John Shahid
Subject: Re: call-process and incremental display of output
Date: Fri, 19 Oct 2018 19:52:23 -0400
User-agent: mu4e 1.1.0; emacs 27.0.50

Stefan Monnier <> writes:

>>> You might like to (setq-local window-point-insertion-type t) in your
>>> buffer (make sure you do it before the buffer is displayed in a window).
>> I'm curious why `save-excursion' doesn't respect the value of
>> `window-point-insertion-type' ?  I was wondering about this for some
>> time now.  The behavior I want is to always append the output to the end
>> of the buffer but not annoy the user if they decide to move the point
>> somewhere else to look at previous output.  In this case the point
>> should stay where it is.  This sounds exactly like what markers are
>> supposed to do.  Unfortunately the marker created by `save-excursion'
>> always has a `nil' insertion type.  This means I have to maintain my own
>> marker in an `unwind-protect' similar to what the compilation mode does.
>> Are there any objections to changing `save-excursion' behavior ?
> I lost you: where do you save-excursion?

Sorry, I should have explained a little bit what I'm trying to do.  I
spin up a curl process that connects to our CI server and display the
log output of a build.  The server stream the log output as a sequence
of json messages that have to be parsed and appended to the buffer.  I
used to do that with the following snippet of code:

    (with-current-buffer log-buffer
        (goto-char (point-max))
        (insert log-line)))

This caused the data to be inserted at the end of the buffer, but I
constantly had to scroll to the end of the buffer in order to follow the

I was aware of this problem for a while but never got chance to tackle
it.  Then, I saw your earlier message about
`window-point-insertion-type' and I decided to try it.  That didn't work
and I think the reason is `save-excursion' creates a marker with
insertion type set to `nil'.

In my earlier message, I was trying to propose making `save-excursion'
set the marker insertion type to `t' if `window-point-insertion-type' is
set to t.

FYI, what I currently have is something like this:

    (let ((pos (copy-marker (point) t)))
        (goto-char (point-max))
        (insert payload))
      (goto-char pos))

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