bug#46171: 27.1; buffer-file-coding-system

bug#46171: 27.1; buffer-file-coding-system

[daniel-f.gordillo--- via Bug reports for GNU Emacs, the Swiss army knife of text editors]

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In Emacs for Windows: I opened a SQL generated file with coding utf-8,
but it's identified as iso-latin-1 (but it's not true). The same file,
in Emacs for gnu/Linux, it's identified as utf-8.


In GNU Emacs 27.1 (build 1, i686-w64-mingw32)
of 2020-08-21 built on CIRROCUMULUS
Repository revision: 86d8d76aa36037184db0b2897c434cdaab1a9ae8
Repository branch: HEAD
Windowing system distributor 'Microsoft Corp.', version 10.0.19041
System Description: Microsoft Windows 10 Enterprise (v10.0.2004.19041.685)

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Quit [2 times]
Quit
Configured using:
'configure --without-dbus --host=i686-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: ESN
  locale-coding-system: cp1252

Major mode: Fundamental

Minor modes in effect:
  tooltip-mode: t
  global-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
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr thingatpt help-fns radix-tree help-mode 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
tango-dark-theme 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 8 55606 26559)
(symbols 24 6362 1)
(strings 16 19700 1846)
(string-bytes 1 563964)
(vectors 8 10462)
(vector-slots 4 135393 15366)
(floats 8 22 261)
(intervals 28 283 35)
(buffers 576 12))


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bug#46171: 27.1; buffer-file-coding-system

[Eli Zaretskii]

> Date: Fri, 29 Jan 2021 12:14:45 +0000
> From: daniel-f.gordillo--- via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> In Emacs for Windows: I opened a SQL generated file with coding utf-8,
> but it's identified as iso-latin-1 (but it's not true). The same file,
> in Emacs for gnu/Linux, it's identified as utf-8.

It isn't always possible to identify the UTF-8 encoding, so when the
default of the locale is not UTF-8 (and it never is on MS-Windows),
Emacs sometimes guesses wrong.

To work around this, if you know the file is encoded in UTF-8, you can
tell Emacs about that:

  C-x RET c utf-8 RET C-x C-f <the-file> RET

OTOH, if SQL files are always encoded in UTF-8 (are they?), we can add
this knowledge to Emacs, assuming these files have some known
file-name extension, or have some telltale string at their beginning.

bug#46171: [External] : bug#46171: 27.1; buffer-file-coding-system

[Drew Adams]

> OTOH, if SQL files are always encoded in UTF-8 (are they?),

No, they are not.

bug#46171: 27.1; buffer-file-coding-system

[Lars Ingebrigtsen]

Eli Zaretskii <eliz@gnu.org> writes:

> It isn't always possible to identify the UTF-8 encoding, so when the
> default of the locale is not UTF-8 (and it never is on MS-Windows),
> Emacs sometimes guesses wrong.
>
> To work around this, if you know the file is encoded in UTF-8, you can
> tell Emacs about that:
>
>   C-x RET c utf-8 RET C-x C-f <the-file> RET
>
> OTOH, if SQL files are always encoded in UTF-8 (are they?), we can add
> this knowledge to Emacs, assuming these files have some known
> file-name extension, or have some telltale string at their beginning.

SQL files can be in any coding system, so we can't really do anything
here on the Emacs side -- sometimes Emacs will guess wrong on the coding
system, and the user will have to provide some hints, as you say here.

So I'm closing this bug report.

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