bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[N. Jackson]

In cc mode, with delete selection mode and electric pair mode both on,
entering a "(" when there is an active selection erroneously deletes the
selection (and inserts "()" in the buffer) rather than inserting a "("
before the selection and a ")" after it. This is inconsistent with the
seemingly correct [1] and useful behaviour in (for example) text mode,
fundamental mode, and lisp mode.

The bug affects both code and in comments.

STEPS TO REPRODUCE:

$ cat > test.c
/* This is a short comment. */
int test(void){
  return 0;
}
^D
$ emacs -Q
M-x delete-selection-mode
M-x electric-pair-mode
C-x f test.c RET
;; Select the word "short" in the first line.
(
;; Now select the "0" in the return statement.
(

EXPECTED RESULT:

/* This is a (short) comment. */
int test(void){
  return (0);
}

OBSERVED RESULT:

/* This is a () comment. */
int test(void){
  return ();
}

[1] http://debbugs.gnu.org/cgi/bugreport.cgi?bug=11520


In GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.14)
 of 2015-07-25 on moondust
Windowing system distributor `Fedora Project', version 11.0.11603000
System Description:	Fedora release 21 (Twenty One)

Configured using:
 `configure --prefix=/home/nlj/local/ --enable-checking=yes,glyphs
 'CFLAGS=-O0 -g3 -ggdb''

Important settings:
  value of $LC_MONETARY: en_DK.utf8
  value of $LC_NUMERIC: en_DK.utf8
  value of $LC_TIME: en_DK.utf8
  value of $LANG: en_CA.utf8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: C/l

Minor modes in effect:
  flyspell-mode: t
  recentf-mode: t
  delete-selection-mode: t
  show-paren-mode: t
  savehist-mode: t
  electric-pair-mode: t
  display-time-mode: t
  display-battery-mode: t
  desktop-save-mode: t
  cua-mode: t
  tooltip-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  size-indication-mode: t
  column-number-mode: t
  line-number-mode: t
  global-visual-line-mode: t
  visual-line-mode: t
  transient-mark-mode: t
  abbrev-mode: t

Recent messages:
Auto-saving...done
Making completion list...
Type C-x 1 to delete the help window.
Undo! [2 times]
Auto-saving...
Updating buffer list...done
Commands: m, u, t, RET, g, k, S, D, Q; q to quit; h for help
Mark set
Mark saved where search started
Mark set
call-interactively: End of buffer

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Features:
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Memory information:
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 (strings 32 143249 27034)
 (string-bytes 1 5112701)
 (vectors 16 49403)
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 (heap 1024 112144 35561))

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Alan Mackenzie]

Hello, N.

In article <mailman.8417.1439731993.904.bug-gnu-emacs@gnu.org> you wrote:
> In cc mode, with delete selection mode and electric pair mode both on,
> entering a "(" when there is an active selection erroneously deletes the
> selection (and inserts "()" in the buffer) rather than inserting a "("
> before the selection and a ")" after it. This is inconsistent with the
> seemingly correct [1] and useful behaviour in (for example) text mode,
> fundamental mode, and lisp mode.

> The bug affects both code and in comments.

And it also affects braces as well as parens.

Thanks for taking the trouble to report this bug, and thanks even more
for making your report so clear and well structured.

> STEPS TO REPRODUCE:

> $ cat > test.c
> /* This is a short comment. */
> int test(void){
>   return 0;
> }
> ^D
> $ emacs -Q
> M-x delete-selection-mode
> M-x electric-pair-mode
> C-x f test.c RET
> ;; Select the word "short" in the first line.
> (
> ;; Now select the "0" in the return statement.
> (

> EXPECTED RESULT:

> /* This is a (short) comment. */
> int test(void){
>   return (0);
> }

> OBSERVED RESULT:

> /* This is a () comment. */
> int test(void){
>   return ();
> }

> [1] http://debbugs.gnu.org/cgi/bugreport.cgi?bug=11520


> In GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.14.14)
>  of 2015-07-25 on moondust
> Windowing system distributor `Fedora Project', version 11.0.11603000
> System Description:     Fedora release 21 (Twenty One)

I think the following patch should fix it.  To apply it, go to the
directory ..../emacs-24.5/lisp and apply the patch from there.  If `patch'
complains at not finding the second file, and prompts you for it, this
will be .../emacs-24.5/lisp/progmodes/cc-cmds.el.  After byte-compiling
both files (either with M-x byte-compile-file from inside emacs, or with
$ emacs -Q -batch -f batch-byte-compile delsel.el progmodes/cc-cmds.el
from a command line), just load the two files.elc into Emacs with
M-x load-file (or restart Emacs).

Would you please confirm that the problem has been fixed, or tell us what
is still not working.  Thanks in advance!

Here's the patch:


diff --git a/lisp/delsel.el b/lisp/delsel.el
index 740b603..6a77d75 100644
--- a/lisp/delsel.el
+++ b/lisp/delsel.el
@@ -231,10 +231,15 @@ See `delete-selection-helper'."
     (delete-selection-helper (and (symbolp this-command)
                                   (get this-command 'delete-selection)))))
 
-(put 'self-insert-command 'delete-selection
-     (lambda ()
-       (not (run-hook-with-args-until-success
-             'self-insert-uses-region-functions))))
+(defun delete-selection-uses-region-p ()
+  "Return non-nil when the current command uses the region.
+This function is intended for use as the value of the
+  `delete-selection' property of a command, and shouldn't be used for
+  anything else."
+  (not (run-hook-with-args-until-success
+        'self-insert-uses-region-functions)))
+
+(put 'self-insert-command 'delete-selection 'delete-selection-uses-region-p)
 
 (put 'insert-char 'delete-selection t)
 (put 'quoted-insert 'delete-selection t)
diff --git a/lisp/progmodes/cc-cmds.el b/lisp/progmodes/cc-cmds.el
index c9f5945..40ec4bd 100644
--- a/lisp/progmodes/cc-cmds.el
+++ b/lisp/progmodes/cc-cmds.el
@@ -2860,13 +2860,18 @@ sentence motion in or near comments and multiline strings."
     (put sym 'delete-selection t)	; for delsel (Emacs)
     (put sym 'pending-delete t)))	; for pending-del (XEmacs)
  '(c-electric-pound
-   c-electric-brace
+;  c-electric-brace
    c-electric-slash
    c-electric-star
    c-electric-semi&comma
    c-electric-lt-gt
    c-electric-colon
-   c-electric-paren))
+;  c-electric-paren
+   ))
+(put 'c-electric-brace 'delete-selection 'delete-selection-uses-region-p)
+(put 'c-electric-brace 'pending-delete 't)
+(put 'c-electric-paren 'delete-selection 'delete-selection-uses-region-p)
+(put 'c-electric-paren 'pending-delete 't)
 (put 'c-electric-delete    'delete-selection 'supersede) ; delsel
 (put 'c-electric-delete    'pending-delete   'supersede) ; pending-del
 (put 'c-electric-backspace 'delete-selection 'supersede) ; delsel


-- 
Alan Mackenzie (Nuremberg, Germany).

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[N. Jackson]

At 12:04 -0300 on Tuesday 2015-08-18, Alan Mackenzie wrote:

> I think the following patch should fix it.

> Would you please confirm that the problem has been fixed, or tell us
> what is still not working. Thanks in advance!

Thanks Alan. Yes, the patch does indeed fix the problem in my Emacs.

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Alan Mackenzie]

Bug fixed in savannah master branch.

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Stefan Monnier]

> +(defun delete-selection-uses-region-p ()

The way I read it, this name says "a function which tells us if
delete-selection uses the region".

> +  "Return non-nil when the current command uses the region.

It's not about "the current command" but about self-insert-command
(which may be the current command or may be called by the current command).

> +(put 'c-electric-brace 'delete-selection 'delete-selection-uses-region-p)
> +(put 'c-electric-brace 'pending-delete 't)
> +(put 'c-electric-paren 'delete-selection 'delete-selection-uses-region-p)
> +(put 'c-electric-paren 'pending-delete 't)

An alternative would be to copy the `delete-selection' (and
`pending-delete') property of `self-insert-command'.  Probably in an
after-load, tho.


        Stefan

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Drew Adams]

> > +(defun delete-selection-uses-region-p ()
> 
> The way I read it, this name says "a function which tells us if
> delete-selection uses the region".

No idea what this is all about, but if this is for
`electric-pair-mode' and not for `delete-selection-mode' then
the name should reflect that - call it `electric-pair-SOMETHING'.

Is this something that `delete-selection-mode' needs?  Or is it
for something else?

> > +  "Return non-nil when the current command uses the region.

What does it mean for a command to "use the region"?

> It's not about "the current command" but about self-insert-command
> (which may be the current command or may be called by the current
> command).

What does it mean for such a command (or any other command) to
"use the region"?  That info should presumably be in the doc string.

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Alan Mackenzie]

Hello, Drew.

On Thu, Aug 20, 2015 at 02:35:43PM -0700, Drew Adams wrote:
> > > +(defun delete-selection-uses-region-p ()
> > 
> > The way I read it, this name says "a function which tells us if
> > delete-selection uses the region".

> No idea what this is all about, ....

It's for when delete-selection-mode and electric-pair-mode are both
enabled.  What was happening (in C Mode, etc.) was that the user would
mark an object and type "(", expecting e-p-m to put a pair of parens
around the marked object; however d-s-m got in first, and deleted
(?killed) the region before the parens were put around the now empty
region.

There was already a solution for this for when "(" is bound to
self-insert-command - this is fairly arcane, and involves setting a
particular variable to function which returns t in the pertinent
circumstances.

This function was previously coded as a lambda.  However, I needed to
use it for the pertinent CC Mode functions too, so I extracted it into a
defun, giving it the name `delete-selection-uses-region-p'.  The
"delete-seleection" bit is the prefix, shared by the other
de\(fun\|var\)s in the file.

> .... but if this is for `electric-pair-mode' and not for
> `delete-selection-mode' then the name should reflect that - call it
> `electric-pair-SOMETHING'.

It's for when BOTH minor modes are enabled, to enable them to play
nicely with eachother.  But it's in delsel.el, hence the prefix.

> Is this something that `delete-selection-mode' needs?  Or is it
> for something else?

See above.

> > > +  "Return non-nil when the current command uses the region.

> What does it mean for a command to "use the region"?

That isn't very good, is it?  It basically means, from e-p-m's point of
view "I'm going to be "using" the region, so don't you go and delete
it!".

> > It's not about "the current command" but about self-insert-command
> > (which may be the current command or may be called by the current
> > command).

> What does it mean for such a command (or any other command) to
> "use the region"?  That info should presumably be in the doc string.

I think you're right, here.  I'll have another look at it.

-- 
Alan Mackenzie (Nuremberg, Germany).

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Drew Adams]

Hi Alan,

Yes, it's a workaround for electric-pair mode. And yes, delete-selection mode got there first. A few decades earlier. ;-)

My point is that this workaround for electric-pair should have an "electric-pair" name, not a "delete-selection" name. It is not something used by delete-selection.

> > > > +(defun delete-selection-uses-region-p ()
> > >
> > > The way I read it, this name says "a function which tells us if
> > > delete-selection uses the region".
> 
> > No idea what this is all about, ....
> 
> It's for when delete-selection-mode and electric-pair-mode are both
> enabled.  What was happening (in C Mode, etc.) was that the user
> would mark an object and type "(", expecting e-p-m to put a pair
> of parens around the marked object; however d-s-m got in first,
> and deleted (?killed) the region before the parens were put around
> the now empty region.
> 
> There was already a solution for this for when "(" is bound to
> self-insert-command - this is fairly arcane, and involves setting a
> particular variable to function which returns t in the pertinent
> circumstances.
> 
> This function was previously coded as a lambda.  However, I needed
> to use it for the pertinent CC Mode functions too, so I extracted
> it into a defun, giving it the name `delete-selection-uses-region-p'.  
> The "delete-seleection" bit is the prefix, shared by the other
> de\(fun\|var\)s in the file.

In what file?  Why is the prefix "delete-selection", and not
"electric-pair"?

> > .... but if this is for `electric-pair-mode' and not for
> > `delete-selection-mode' then the name should reflect that -\
> > call it `electric-pair-SOMETHING'.
> 
> It's for when BOTH minor modes are enabled, to enable them to play
> nicely with eachother.  But it's in delsel.el, hence the prefix.

It's for electric-pair to move into the delete-selection
neighborhood.  It's an electric-pair thing.  Delete-selection
mode doesn't need it - never has.

> > Is this something that `delete-selection-mode' needs?
> > Or is it for something else?
> 
> See above.

AFAICT, it is not for delete-selection mode.  It is a hack
so that electric-pair mode can adapt to delete-selection 
mode.  Nothing wrong with that, in principle.  When a new
feature is added, it often has to accommodate existing
behavior.  My point is that the name should reflect the
fact that this is a workaround for electric-pair mode, so
that it DTRT.  If you had to add another workaround for e-p
mode, so that it DTRT with commas or whatever, that would
be no different.  Such things are about e-p; their names
should reflect that.

If you also want to refer, in the name, to the thing you
are working around for e-p mode, that's OK, but the prefix
of the name should be e-p: `elec-pair-hack-to-tolerate-delsel'
or whatever.

> > > > +  "Return non-nil when the current command uses the region.
> 
> > What does it mean for a command to "use the region"?
> 
> That isn't very good, is it?  It basically means, from e-p-m's
> point of view "I'm going to be "using" the region, so don't
> you go and delete it!".

That still doesn't speak to what "using the region" means.
It sounds like what is important is that you are protecting
the region for e-p.  If so, the name and description should
reflect that need, not just "using the region".

> > > It's not about "the current command" but about
> > > self-insert-command (which may be the current command or
> > > may be called by the current command).
> 
> > What does it mean for such a command (or any other command) to
> > "use the region"?  That info should presumably be in the doc
> > string.
> 
> I think you're right, here.  I'll have another look at it.

Anyway, it's not very important.  Just one opinion.  I'd
recommend writing the explanation and names from the point
of view of e-p (only).

HTH - Drew

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Stefan Monnier]

> My point is that this workaround for electric-pair should have an
> "electric-pair" name, not a "delete-selection" name.  It is not something
> used by delete-selection.

No.  It's a feature of delete-selection (in the form of a hook).
Look at the code: it doesn't say anything about electric-pair.
This feature was added for electric-pair, indeed, but it's a feature of
delete-selection.

elec-pair.el has the other half of code (added to delete-selection's
hook), using the proper prefix.


        Stefan

bug#21275: 24.5; Selection deleted with electric pair mode in cc mode

[Drew Adams]

> > My point is that this workaround for electric-pair should have an
> > "electric-pair" name, not a "delete-selection" name.  It is not
> > something used by delete-selection.
> 
> No.  It's a feature of delete-selection (in the form of a hook).
> Look at the code: it doesn't say anything about electric-pair.
> This feature was added for electric-pair, indeed, but it's a feature
> of delete-selection.
> 
> elec-pair.el has the other half of code (added to delete-selection's
> hook), using the proper prefix.

OK, my mistake, I guess.  Thanks for thinking about it.