bug#34704: 26.1; Wrong line endings detected for XML files

[Akkana Peck]

I often use emacs to edit GPX files produced by OsmAnd.
Emacs displays these files with ^M at the end, failing to detect
the proper newlines. od shows the file as having \r\n (^J^M)
at the end of every line.

I initially thought this was because the final line of the file
lacks any newline characters, but if I edit the file and write it,
emacs adds a final ^J^M, and if I then try to read that file back
into emacs it still fails to detect the proper line endings, and
shows the ^M on every line.

The problem is related to the file containing XML:
if I edit the file and change all the < > to ( ) then open the file,
it opens in Fundamental mode and emacs uses DOS encoding and doesn't
show the ^M characters. But if I open the file normally (it uses nXML
mode) then switch to Fundamental, that doesn't fix the erroneous
newline detection. Of course I can fix it manually, but I'd like
to find a way to get emacs to open the file properly without my
needing to run extra commands.

I asked about this on #emacs and a helpful person commented:

    | I think auto-coding-functions is a problem.
    | sgml-xml-auto-coding-function specifically.
    | mule.el: (memq detected '(utf-8 'utf-8-with-signature 'utf-8-hfs 
undecided))
    | That looks a bit funny to me.
    | Ugh, no, it's both sgml-* functions in auto-coding-functions?
    | I must have screwed something up, sgml-html-meta-auto-coding-function 
returns nil for me.
    | But sgml-xml-auto-coding-function returns utf-8-unix.
    | I don't know enough about how Emacs chooses character sets to speculate 
at how this should be fixed, but I *think* that function should probably return 
utf-8 not utf-8-unix.

I'm attaching a small test file that shows the problem.



In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.4)
 of 2019-02-03, modified by Debian built on zam904
Windowing system distributor 'The X.Org Foundation', version 11.0.12003000
System Description:     Debian GNU/Linux buster/sid

Recent messages:
Quit [2 times]
Saving file /tmp/test.paren...
Wrote /tmp/test.paren
Using vacuous schema
Type C-x 1 to delete the help window.
Using vacuous schema
Quit
Missing space after name token
Error during redisplay: (jit-lock-function 59) signaled (cl-assertion-failed 
(bobp))
Entering debugger...

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --enable-libsystemd --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --build
 x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
 --libexecdir=/usr/lib --localstatedir=/var/lib
 --infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
 --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs-26.1+1=. -fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 THREADS LIBSYSTEMD LCMS2

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

Major mode: nXML

Minor modes in effect:
  recentf-mode: t
  dubcaps-mode: t
  auto-insert-mode: t
  global-keys-minor-mode: t
  delete-selection-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

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Features:
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Memory information:
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test.gpx
Description: Text document