bug#68751: 29.1; "\x0e0" is a multibyte string

bug#68751: 29.1; "\x0e0" is a multibyte string

[Christopher Yeleighton]

M-: (multibyte-string-p "\x0e0") RET

 > t


In GNU Emacs 29.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.38,
cairo version 1.17.8)
Windowing system distributor 'The X.Org Foundation', version 11.0.12101010
System Description: Arch Linux

Configured using:
'configure --sysconfdir=/etc --prefix=/usr --libexecdir=/usr/lib
--with-tree-sitter --localstatedir=/var --with-cairo
--disable-build-details --with-harfbuzz --with-libsystemd
--with-modules --with-x-toolkit=gtk3 'CFLAGS=-march=x86-64
-mtune=generic -O2 -pipe -fno-plt -fexceptions -Wp,-D_FORTIFY_SOURCE=2
-Wformat -Werror=format-security -fstack-clash-protection
-fcf-protection -g
-ffile-prefix-map=/build/emacs/src=/usr/src/debug/emacs -flto=auto'
'LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now -flto=auto''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 M17N_FLT MODULES NOTIFY INOTIFY
PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS
TREE_SITTER WEBP X11 XDBE XIM XINPUT2 XPM GTK3 ZLIB

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

Major mode: Info

Minor modes in effect:
shell-dirtrack-mode: t
tooltip-mode: t
global-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
isearch-fold-quotes-mode: t
global-font-lock-mode: t
font-lock-mode: t
blink-cursor-mode: t
buffer-read-only: t
line-number-mode: t
indent-tabs-mode: t
transient-mark-mode: t
auto-composition-mode: t
auto-encryption-mode: t
auto-compression-mode: t

Load-path shadows:
None found.

Features:
(xref project lpr thai-util thai-word repeat mailalias mailclient
textsec uni-scripts idna-mapping ucs-normalize uni-confusable
textsec-check facemenu shadow sort mail-extr emacsbug message yank-media
puny rfc822 mml mml-sec epa derived epg rfc6068 epg-config gnus-util
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils browse-url url url-proxy url-privacy url-expand url-methods
url-history url-cookie generate-lisp-file url-domsuf url-util url-parse
url-vars mailcap mule-util info tar-mode arc-mode archive-mode sh-script
rx smie treesit executable files-x conf-mode shell pcomplete comint
ansi-osc ansi-color ring dired-aux dired dired-loaddefs noutline outline
icons two-column kmacro debug backtrace find-func face-remap shortdoc
text-property-search cl-extra cl-print erc-lang erc-goodies erc iso8601
auth-source cl-seq eieio eieio-core cl-macs password-cache json map pp
format-spec erc-backend erc-networks byte-opt gv bytecomp byte-compile
erc-common erc-compat erc-loaddefs thingatpt help-fns radix-tree
jka-compr misearch multi-isearch time-date subr-x rfc1345 quail
help-mode cl-loaddefs cl-lib rmc iso-transl tooltip cconv 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 nadvice seq simple cl-generic
indonesian philippine 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 abbrev obarray oclosure cl-preloaded button loaddefs
theme-loaddefs faces cus-face macroexp files window text-properties
overlay sha1 md5 base64 format env code-pages mule custom widget keymap
hashtable-print-readable backquote threads dbusbind inotify lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit xinput2 x multi-tty make-network-process
emacs)

Memory information:
((conses 16 514130 81836)
(symbols 48 26162 44)
(strings 32 129312 5724)
(string-bytes 1 2808230)
(vectors 16 59943)
(vector-slots 8 1889204 140248)
(floats 8 953 203)
(intervals 56 27501 657)
(buffers 984 37))

bug#68751: Acknowledgement (29.1; "\x0e0" is a multibyte string)

[Christopher Yeleighton]

Info (elisp) Non-ASCII in Strings says:

 > If a string constant contains hexadecimal or octal escape sequences, 
and these
 > escape sequences all specify unibyte characters (i.e., less than 256),
 > and there are no other literal non-ASCII characters or Unicode-style
 > escape sequences in the string, then Emacs automatically assumes that it
 > is a unibyte string.

I believe it should say:

| (i.e., less than 256 and octal or written with 2 hexadecimal digits),

and additionally

| Unibyte characters embedded in multibyte string constants evaluate to 
private character codes,
| e.g. "\x0a0\xa0" equals "\x0a0\x3fffa0".

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bug#68751: 29.1; "\x0e0" is a multibyte string

[Eli Zaretskii]

> Date: Sat, 27 Jan 2024 06:23:45 +0000
> From: Christopher Yeleighton <giecrilj@stegny.2a.pl>
> 
> M-: (multibyte-string-p "\x0e0") RET
> 
>  > t

Why do you think this is a problem?  U+0E0E is à, a non-ASCII
character, so it has a multibyte representation.

bug#68751: 29.1; "\x0e0" is a multibyte string

[Krzysztof Żelechowski]

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bug#68751: 29.1; "\x0e0" is a multibyte string

[Eli Zaretskii]

> Date: Sat, 27 Jan 2024 06:46:36 +0000
> From: Christopher Yeleighton <giecrilj@stegny.2a.pl>
> 
> Info (elisp) Non-ASCII in Strings says:
> 
>  > If a string constant contains hexadecimal or octal escape sequences, 
> and these
>  > escape sequences all specify unibyte characters (i.e., less than 256),
>  > and there are no other literal non-ASCII characters or Unicode-style
>  > escape sequences in the string, then Emacs automatically assumes that it
>  > is a unibyte string.
> 
> I believe it should say:
> 
> | (i.e., less than 256 and octal or written with 2 hexadecimal digits),

Right.  I modified the text to that effect.

> and additionally
> 
> | Unibyte characters embedded in multibyte string constants evaluate to 
> private character codes,
> | e.g. "\x0a0\xa0" equals "\x0a0\x3fffa0".

I didn't make this change because I don't see how it is useful.
First, "evaluate" is confusing here.  Also, "private character codes"
is confusing/incorrect, as it could be interpreted to mean Emacs
somehow uses the PUA of Unicode codespace, which it doesn't.  Finally,
when Emacs converts from a single-byte representation of a raw byte to
its multibyte representation is an obscure matter largely defined by
ad-hoc compatibility considerations, and doesn't belong to the ELisp
manual.

I think this bug can be closed now.