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Re: "Staying in the same place"

From: Lars Magne Ingebrigtsen
Subject: Re: "Staying in the same place"
Date: Mon, 04 Apr 2016 08:09:31 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1.50 (gnu/linux)

Lars Magne Ingebrigtsen <address@hidden> writes:

> I wonder if anybody has thought about the issue in a more general way --
> by providing a mechanism to save (perhaps a lot) of context, and then
> trying to go back to the same context again after regenerating the
> buffer, in a ... fuzzy way.

Thinking about this a bit more, I think it's difficult to see a way to
do this generally without support from each mode.  However:

In general, if the buffer reflects things that don't really change a
lot, just recording the current line (and the next and previous ten
lines, say), would DWIM.

For buffers where there is a strong "identity" (say, file names in dired
and bug numbers in debbugs mode), the mode could provide a way to give
those identities to `revert-buffer' (and a way to restore point).

Take compilation modes, for instance.  Let's say there's a variable
`revert-buffer-context-function'.  The mode would return a list of error

make -k 
  CC       vm-limit.o
  CC       dispnew.o
  CC       frame.o
frame.c: In function 'x_set_frame_parameters':
frame.c:3296:25: warning: 'height' may be used uninitialized in this function 
frame.c:3296:25: warning: 'width' may be used uninitialized in this function 
  CC       scroll.o
  CC       xdisp.o
xdisp.c: In function 'move_it_in_display_line_to':
xdisp.c:8556:13: warning: 'closest_pos' may be used uninitialized in this 
function [-Wmaybe-uninitialized]
xdisp.c: In function 'display_line':
xdisp.c:20348:8: warning: 'max_bpos' may be used uninitialized in this function 

The list would perhaps be '("^frame.c:3296:" "^xdisp.c:8556:" ...).
`revert-buffer' would then basically do

(let ((context (funcall revert-buffer-context-function)))
  (funcall revert-buffer-function)
  (revert-buffer-restore-point context))

which would use those regexps to put point somewhere DWIM-ey.  And there
could be a `revert-buffer-restore-point-function' variable, too, if the
mode needs a more specialised way to use the context.

Of course, the this specific example, this wouldn't work, since
compilation is asynchronous, but the compilation mode could just use the
context itself from the filter.  Or the sentinel.  Or something.


But I think this approach might work for many modes...  perhaps...

(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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