bug#15396: permanent-local truncate-lines

bug#15396: permanent-local truncate-lines

[Glenn Morris]

Package: emacs
Version: 24.3
Severity: wishlist

I wish truncate-lines was permanent local. Motivation:

emacs -Q foo.txt
   where foo.txt has lines longer than the frame width.
M-x toggle-truncate-lines
   now lines are truncated
M-x revert-buffer   ; or even just change mode
   now lines are untruncated again, grr

(Simply marking it permanent-local doesn't seem to be enough.)

bug#15396: permanent-local truncate-lines

[Drew Adams]

> I wish truncate-lines was permanent local. Motivation:
> M-x toggle-truncate-lines ; now lines are truncated
> M-x revert-buffer   ; now lines are untruncated again

FWIW, the manual says that "Permanent locals are appropriate for data
pertaining to where the file came from or how to save it, rather than
with how to edit the contents."

Display seems to be related more to how to edit than to where the file
came from or how to save it.

Not that that guideline is a biblical injunction, to be followed blindly,
but its characterization does not seem to apply here.  Dunno whether
it is appropriate to consider the guideline here.

bug#15396: permanent-local truncate-lines

[Stefan Monnier]

> I wish truncate-lines was permanent local.  Motivation:
> emacs -Q foo.txt
>    where foo.txt has lines longer than the frame width.
> M-x toggle-truncate-lines
>    now lines are truncated
> M-x revert-buffer   ; or even just change mode
>    now lines are untruncated again, grr

I don't mind so much that truncate-lines gets reset when I change major
mode because I very rarely change major-mode, but recently I started
feeling like M-x revert-buffer should usually not change major-mode.
After all, I can call M-x normal-mode if I really need that extra step.


        Stefan

bug#15396: permanent-local truncate-lines

[Stefan Monnier]

> FWIW, the manual says that "Permanent locals are appropriate for data
> pertaining to where the file came from or how to save it, rather than
> with how to edit the contents."

I think this makes a lot of sense for permanent-local settings made by
major-mode code.  But if the user calls M-x toggle-truncate-lines,
presumably it's because he finds the text to be more readable this way,
which will presumably still be the case after he changes major-mode.

IOW, maybe it's toggle-truncate-lines which should try and arrange for
the settings to survive a change of major-mode.


        Stefan

bug#15396: permanent-local truncate-lines

[Glenn Morris]

Glenn Morris wrote:

> I wish truncate-lines was permanent local. Motivation:
>
> emacs -Q foo.txt
>    where foo.txt has lines longer than the frame width.
> M-x toggle-truncate-lines
>    now lines are truncated
> M-x revert-buffer   ; or even just change mode
>    now lines are untruncated again, grr

Here's a patch to enable this.

--- i/src/buffer.c
+++ w/src/buffer.c
@@ -5128,7 +5128,9 @@ struct mmap_region
   XSETFASTINT (BVAR (&buffer_local_flags, selective_display), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, selective_display_ellipses), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, tab_width), idx); ++idx;
-  XSETFASTINT (BVAR (&buffer_local_flags, truncate_lines), idx); ++idx;
+  XSETFASTINT (BVAR (&buffer_local_flags, truncate_lines), idx);
+  /* Make this one a permanent local.  */
+  buffer_permanent_local_flags[idx++] = 1;
   XSETFASTINT (BVAR (&buffer_local_flags, word_wrap), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, ctl_arrow), idx); ++idx;
   XSETFASTINT (BVAR (&buffer_local_flags, fill_column), idx); ++idx;