bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

[Corwin Brust]

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In Dired, ERC, and, I assume, any read-only buffer the default behavior of
mouse-3 causes errors (E.g. "kill-region: Buffer is read-only: #<buffer
*Messages*>").

The attached patch attempts to prevent this by detecting a
read-only-buffer.  Unfortunately, it seems that ERC has some other means
of causing its buffers to be rendered read-only that doesn't affect
this var, thus the special-case logic.  I tested with dired, erc, and
(regression tested) while composing this bug report.

Are there other edge cases like erc-mode hanging around, where
read-only-buffer might not be accurate?  Is this oddity with ERC worth a
separate bug report?  Finally, s there a more elegant way to special
case whatever erc-mode is doing?

This is my first attempt at submitting a patch.  I will dig a bit more
into my own questions, above; tia for tips, suggestions, etc.

In GNU Emacs 27.1 (build 1, x86_64-w64-mingw32)
 of 2020-08-21 built on CIRROCUMULUS
Repository revision: 86d8d76aa36037184db0b2897c434cdaab1a9ae8
Repository branch: HEAD
Windowing system distributor 'Microsoft Corp.', version 10.0.18363
System Description: Microsoft Windows 10 Home (v10.0.1909.18363.1082)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY W32NOTIFY ACL GNUTLS LIBXML2
HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS MODULES THREADS JSON PDUMPER LCMS2 GMP

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-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
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs text-property-search time-date
subr-x seq byte-opt gv bytecomp byte-compile cconv mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-loaddefs
cl-lib sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils
tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win w32-vars
term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads w32notify w32 lcms2 multi-tty make-network-process
emacs)

Memory information:
((conses 16 46659 8583)
 (symbols 48 6075 1)
 (strings 32 16982 2021)
 (string-bytes 1 519943)
 (vectors 16 9274)
 (vector-slots 8 123598 13156)
 (floats 8 22 312)
 (intervals 56 222 0)
 (buffers 1000 12))


Corwin

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diff -u "c:/emacs/share/emacs/27.1/lisp/mouse.el-27.1" "c:/emacs/share/emacs/27.1/lisp/mouse.el"
--- c:/emacs/share/emacs/27.1/lisp/mouse.el-27.1	2020-10-07 05:13:58.000000000 -0500
+++ c:/emacs/share/emacs/27.1/lisp/mouse.el	2020-10-07 05:28:12.511318900 -0500
@@ -1601,8 +1601,10 @@
 previous region was just saved to the kill ring).
 
 If this command is called a second consecutive time with the same
-CLICK position, kill the region (or delete it
-if `mouse-drag-copy-region' is non-nil)."
+CLICK position, kill the region (or delete it if
+`mouse-drag-copy-region' is non-nil).  When buffer is
+read-only (or an `erc-mode' derived mode), use `kill-ring-save'
+instead of `kill-region'."
   (interactive "e")
   (mouse-minibuffer-check click)
   (let* ((posn     (event-start click))
@@ -1628,7 +1630,9 @@
           ;; Region already saved in the previous click;
           ;; don't make a duplicate entry, just delete.
           (funcall region-extract-function 'delete-only)
-        (kill-region (mark t) (point) 'region))
+        (if (or buffer-read-only (derived-mode-p 'erc-mode))
+	    (kill-ring-save (mark t) (point) 'region)
+	  (kill-region (mark t) (point) 'region)))
       (setq mouse-selection-click-count 0)
       (setq mouse-save-then-kill-posn nil))
 

Diff finished.  Wed Oct  7 05:31:50 2020

bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

[Noam Postavsky]

Corwin Brust <corwin@bru.st> writes:

> In Dired, ERC, and, I assume, any read-only buffer the default behavior of
> mouse-3 causes errors (E.g. "kill-region: Buffer is read-only: #<buffer
> *Messages*>").

I think you just need to set the kill-read-only-ok option.

    kill-read-only-ok is a variable defined in ‘simple.el’.
    Its value is nil

    Documentation:
    Non-nil means don’t signal an error for killing read-only text.

> Unfortunately, it seems that ERC has some other means of causing its
> buffers to be rendered read-only that doesn't affect this var, thus
> the special-case logic.

I'm guessing ERC marks only some of text as read-only via text
properties.

bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

[Lars Ingebrigtsen]

Noam Postavsky <npostavs@gmail.com> writes:

> I think you just need to set the kill-read-only-ok option.
>
>     kill-read-only-ok is a variable defined in ‘simple.el’.
>     Its value is nil
>
>     Documentation:
>     Non-nil means don’t signal an error for killing read-only text.

So I think this works as designed, and I'm closing this bug report.

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

bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

[Corwin Brust]

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Hi Lars,

Apologies for not having followed-up on this and thank you for lending it
your attention.

On Tue, Jan 26, 2021 at 11:37 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:

> Noam Postavsky <npostavs@gmail.com> writes:
>
> > I think you just need to set the kill-read-only-ok option.
> >
> >     kill-read-only-ok is a variable defined in ‘simple.el’.
> >     Its value is nil
> >
> >     Documentation:
> >     Non-nil means don’t signal an error for killing read-only text.
>
> So I think this works as designed, and I'm closing this bug report.
>

I disagree this behavior makes sense.

Should it be the users responsibility to set this variable (in some hook?
which?) for any buffers that default to read-only?

Again, thanks!


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


-- 
*Corwin*
*corwin@bru.st <corwin@bru.st>*

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bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

[Lars Ingebrigtsen]

Corwin Brust <corwin@bru.st> writes:

> Should it be the users responsibility to set this variable (in some
> hook? which?) for any buffers that default to read-only?

Yes.  Some buffers have read-only text, and killing that text will
signal an error (by design), whether you kill the text using the mouse
or with `C-w'.  If the user wants to be able to kill the text, then the
user should set that variable.

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

bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

[Corwin Brust]

Thanks again Lars.

On Thu, Jan 28, 2021 at 11:02 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:
>
> Corwin Brust <corwin@bru.st> writes:
>
> > Should it be the users responsibility to set this variable (in some
> > hook? which?) for any buffers that default to read-only?
>
> Yes.  Some buffers have read-only text, and killing that text will
> signal an error (by design), whether you kill the text using the mouse
> or with `C-w'.  If the user wants to be able to kill the text, then the
> user should set that variable.

Would you recommend packages such as ERC (or dired?) that essentially
create only read-only buffers to set this such that unconfigured
defaults don't lead to a user-error?

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


Regards,
Corwin

bug#43844: 27.1; Mouse-3 avoid "Buffer is read-only" *patch*

[Lars Ingebrigtsen]

Corwin Brust <corwin@bru.st> writes:

> Would you recommend packages such as ERC (or dired?) that essentially
> create only read-only buffers to set this such that unconfigured
> defaults don't lead to a user-error?

I'm not sure what you mean here?  Buffers that make text read-only do so
because the person who wrote that mode thinks that's a good design
decision.  As usual, Emacs allows users to override anything if they
want to, and `kill-read-only-ok' is the provided user override.

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