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Subject: bug#52459: 28.0.90; prin1-to-string does not escape bidi control characters despite print-escape-control-characters=t
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1. Start emacs -Q
2. Enter the following in the scratch buffer:
(let ((print-escape-control-characters t))
  (prin1-to-string bidi-directional-controls-chars))
3. Evaluate. The bidi control characters are not escaped despite
print-escape-control-characters=t.

The bidi characters should probably be treated as control characters
since they have the Bidi_Control property according to the Unicode
standard.

If it is undesirable to treat bidi control characters like other control
characters it may make sense to introduce another print configuration
variable, print-escape-all-control-characters or
print-escape-bidi-control-characters?

In GNU Emacs 28.0.90 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5,
cairo version 1.16.0)
 of 2021-12-05 built on projects
Repository revision: 34f56561372d83b71dcaff1cdf5d9264ba38fa0e
Repository branch: emacs-28
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Configured using:
 'configure --prefix=/home/user/emacs/install --with-cairo'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG
LIBSELINUX LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG SECCOMP SOUND
THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM XPM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  eldoc-mode: t
  show-paren-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
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg rfc6068 epg-config gnus-util rmail
rmail-loaddefs auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache json map 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 sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils thingatpt
help-fns radix-tree help-mode cl-loaddefs cl-lib two-column iso-transl
tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/x-win x-win term/common-win x-dnd
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax 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 emoji-zwj charscript
charprop case-table epa-hook jka-cmpr-hook help simple abbrev obarray
cl-preloaded nadvice button loaddefs faces cus-face macroexp files
window text-properties overlay sha1 md5 base64 format env code-pages
mule custom widget hashtable-print-readable backquote threads dbusbind
inotify dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process emacs)

Memory information:
((conses 16 57250 10751)
 (symbols 48 6852 1)
 (strings 32 21147 1607)
 (string-bytes 1 651816)
 (vectors 16 13342)
 (vector-slots 8 183349 13347)
 (floats 8 22 48)
 (intervals 56 260 1)
 (buffers 992 13))

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From: help-debbugs@HIDDEN (GNU bug Tracking System)
To: Daniel Mendler <mail@HIDDEN>
Subject: bug#52459: Acknowledgement (28.0.90; prin1-to-string does not
 escape bidi control characters despite print-escape-control-characters=t)
Message-ID: <handler.52459.B.16393400018507.ack <at> debbugs.gnu.org>
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Date: Sun, 12 Dec 2021 20:14:01 +0000

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Message sent to bug-gnu-emacs@HIDDEN:

Subject: bug#52459: 28.0.90; prin1-to-string does not escape bidi control characters despite print-escape-control-characters=t
Resent-From: Eli Zaretskii <eliz@HIDDEN>
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Date: Sun, 12 Dec 2021 22:42:06 +0200
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From: Eli Zaretskii <eliz@HIDDEN>
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 from Daniel Mendler on Sun, 12 Dec 2021 21:13:12 +0100)
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> From: Daniel Mendler <mail@HIDDEN>
> Date: Sun, 12 Dec 2021 21:13:12 +0100
> 
> 1. Start emacs -Q
> 2. Enter the following in the scratch buffer:
> (let ((print-escape-control-characters t))
>   (prin1-to-string bidi-directional-controls-chars))
> 3. Evaluate. The bidi control characters are not escaped despite
> print-escape-control-characters=t.
> 
> The bidi characters should probably be treated as control characters
> since they have the Bidi_Control property according to the Unicode
> standard.

print-escape-control-characters is about ASCII control characters, not
about Unicode fomatting controls.

> If it is undesirable to treat bidi control characters like other control
> characters it may make sense to introduce another print configuration
> variable, print-escape-all-control-characters or
> print-escape-bidi-control-characters?

I don't think it's desirable.  Those formatting controls have starkly
different roles that ASCII control characters, and we already have
features to make them stand out on display.  Moreover, escape
sequences are not well-defined for codepoints beyond a single byte.

So I don't think we should do anything here, and we should close the
bug.

Message sent to bug-gnu-emacs@HIDDEN:

Subject: bug#52459: 28.0.90; prin1-to-string does not escape bidi control characters despite print-escape-control-characters=t
Resent-From: Daniel Mendler <mail@HIDDEN>
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Cc: 52459 <at> debbugs.gnu.org
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 <83v8ztmu75.fsf@HIDDEN>
From: Daniel Mendler <mail@HIDDEN>
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Date: Sun, 12 Dec 2021 22:11:38 +0100
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>> 1. Start emacs -Q
>> 2. Enter the following in the scratch buffer:
>> (let ((print-escape-control-characters t))
>>   (prin1-to-string bidi-directional-controls-chars))
>> 3. Evaluate. The bidi control characters are not escaped despite
>> print-escape-control-characters=t.
>>
>> The bidi characters should probably be treated as control characters
>> since they have the Bidi_Control property according to the Unicode
>> standard.
> 
> print-escape-control-characters is about ASCII control characters, not
> about Unicode fomatting controls.

I see, but this is not a satisfactory answer.

>> If it is undesirable to treat bidi control characters like other control
>> characters it may make sense to introduce another print configuration
>> variable, print-escape-all-control-characters or
>> print-escape-bidi-control-characters?
> 
> I don't think it's desirable.  Those formatting controls have starkly
> different roles that ASCII control characters, and we already have
> features to make them stand out on display.  Moreover, escape
> sequences are not well-defined for codepoints beyond a single byte.
> 
> So I don't think we should do anything here, and we should close the
> bug.

I disagree. I would like to turn this report into a feature request
then. I've observed that multiple packages which escape strings and
print them for debugging or help purposes have difficulties with bidi
characters. All I would like to have is a way to print strings safely,
such that control characters (any kind of control characters, ascii or
unicode) do not affect the output.

Example packages which are affected by this issue are for example the
Helpful package, which provides an enhanced Help buffer. Another package
affected by the issue is the Marginalia package which adds annotations
to `describe-variable` in the minibuffer. The annotations show the
variable value. I would like to print the variable values in a safe way
which does not mess up the display. Instead of "string" these packages
show "str"gnandallthatfollowsisgarbage. How is this supposed to be done?

I propose the addition of an additional variable which configures
prin1-string such that all control characters which affect the display
in special ways are escaped. Is there an alternative approach to achieve
this goal?

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Subject: bug#52459: 28.0.90; prin1-to-string does not escape bidi control characters despite print-escape-control-characters=t
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On 12/12/21 10:11 PM, Daniel Mendler wrote:
> Example packages which are affected by this issue are for example the
> Helpful package, which provides an enhanced Help buffer. Another package
> affected by the issue is the Marginalia package which adds annotations
> to `describe-variable` in the minibuffer. The annotations show the
> variable value. I would like to print the variable values in a safe way
> which does not mess up the display. Instead of "string" these packages
> show "str"gnandallthatfollowsisgarbage. How is this supposed to be done?
> 
> I propose the addition of an additional variable which configures
> prin1-string such that all control characters which affect the display
> in special ways are escaped. Is there an alternative approach to achieve
> this goal?

There is actually one function which comes close in functionality -
`bidi-string-mark-left-to-right`. However this function is not really a
pure string manipulation function since it adds display properties. So
this function can only be used if the string is directly displayed as
is. The function is not a good fit if the resulting string is
manipulated further, truncated, etc.

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Subject: bug#52459: 28.0.90; prin1-to-string does not escape bidi control characters despite print-escape-control-characters=t
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> From: Daniel Mendler <mail@HIDDEN>
> Cc: 52459 <at> debbugs.gnu.org
> Date: Sun, 12 Dec 2021 22:33:50 +0100
> 
> On 12/12/21 10:11 PM, Daniel Mendler wrote:
> > Example packages which are affected by this issue are for example the
> > Helpful package, which provides an enhanced Help buffer. Another package
> > affected by the issue is the Marginalia package which adds annotations
> > to `describe-variable` in the minibuffer. The annotations show the
> > variable value. I would like to print the variable values in a safe way
> > which does not mess up the display. Instead of "string" these packages
> > show "str"gnandallthatfollowsisgarbage. How is this supposed to be done?
> > 
> > I propose the addition of an additional variable which configures
> > prin1-string such that all control characters which affect the display
> > in special ways are escaped. Is there an alternative approach to achieve
> > this goal?
> 
> There is actually one function which comes close in functionality -
> `bidi-string-mark-left-to-right`. However this function is not really a
> pure string manipulation function since it adds display properties. So
> this function can only be used if the string is directly displayed as
> is. The function is not a good fit if the resulting string is
> manipulated further, truncated, etc.

Sorry, I don't understand.  The examples you provided are of text
being displayed.  Which is expected, since these controls have no
other effect _except_ when the text is displayed.  So why isn't the
existing function bidi-string-mark-left-to-right (which was introduced
precisely for the situations like you describe, and is actually used
in Emacs for those purposes) the solution for the class of problems
that you described?

And can we agree that displaying these characters as escapes would not
solve the problems you had in mind, so it is off the table for the
rest of this discussion?

Last modified: Mon, 13 Dec 2021 12:30:02 UTC

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