bug#64102: 28.2; fails to find pathname with a sub dir as symlink and with parent dir ('..')

[Jacob Burckhardt]

Reproduce the bug by running this:

mkdir -p /tmp/usr2/lib/gcc/x86_64-linux-gnu/12
mkdir /tmp/usr2/include
echo symbolic link test > /tmp/usr2/include/test.h
\ln -s usr2/lib /tmp/lib2
cat /tmp/lib2/gcc/x86_64-linux-gnu/12/../../../../include/test.h
emacs -q /tmp/lib2/gcc/x86_64-linux-gnu/12/../../../../include/test.h

Emacs failed to display the content of that file in a buffer.  Since the above 
cat command shows the contents, Emacs should be able to show it as well.  The 
following bug is similar and includes some explanations that also apply to my 
bug.

https://debbugs.gnu.org/cgi/bugreport.cgi?bug=8035

Note that the following code succeeds.  You might consider using code like this 
to fix the bug:

(find-file (file-truename 
"/tmp/lib2/gcc/x86_64-linux-gnu/12/../../../../include/test.h"))




In GNU Emacs 28.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.37, cairo 
version 1.16.0)
 of 2023-05-13, modified by Debian built on x86-ubc-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12101007
System Description: Debian GNU/Linux 12 (bookworm)

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-libsystemd --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/28.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/28.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils
 --with-native-compilation --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-libsystemd --with-pop=yes
 
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/28.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/28.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils
 --with-native-compilation --with-cairo --with-x=yes
 --with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -ffile-prefix-map=/build/emacs-mPr7Vr/emacs-28.2+1=. -fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'

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

Important settings:
  locale-coding-system: nil

Major mode: Fundamental

Minor modes in effect:
  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
  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
  indent-tabs-mode: t
  transient-mark-mode: t

Load-path shadows:
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/usr/share/emacs/site-lisp/llvm-11/tablegen-mode
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/usr/share/emacs/site-lisp/vm/vcard hides /usr/share/emacs/site-lisp/vm.in/vcard
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/usr/share/emacs/site-lisp/vm/vm hides /usr/share/emacs/site-lisp/vm.in/vm
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/usr/share/emacs/site-lisp/vm/vm-vcard hides 
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/usr/share/emacs/site-lisp/vm/vm-mouse hides 
/usr/share/emacs/site-lisp/vm.in/vm-mouse
/usr/share/emacs/site-lisp/vm/vm-message hides 
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/usr/share/emacs/site-lisp/vm/vm-delete hides 
/usr/share/emacs/site-lisp/vm.in/vm-delete
/usr/share/emacs/site-lisp/vm/tapestry hides 
/usr/share/emacs/site-lisp/vm.in/tapestry
/usr/share/emacs/site-lisp/vm/vm-reply hides 
/usr/share/emacs/site-lisp/vm.in/vm-reply
/usr/share/emacs/site-lisp/vm/vm-edit hides 
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/usr/share/emacs/site-lisp/vm/vm-search hides 
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/usr/share/emacs/site-lisp/vm/vm-imap hides 
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/usr/share/emacs/site-lisp/vm/vm-sort hides 
/usr/share/emacs/site-lisp/vm.in/vm-sort
/usr/share/emacs/site-lisp/vm/vm-window hides 
/usr/share/emacs/site-lisp/vm.in/vm-window
/usr/share/emacs/site-lisp/vm/vm-ps-print hides 
/usr/share/emacs/site-lisp/vm.in/vm-ps-print
/usr/share/emacs/site-lisp/vm/vm-pop hides 
/usr/share/emacs/site-lisp/vm.in/vm-pop
/usr/share/emacs/site-lisp/vm/vm-save hides 
/usr/share/emacs/site-lisp/vm.in/vm-save
/usr/share/emacs/site-lisp/vm/vm-folder hides 
/usr/share/emacs/site-lisp/vm.in/vm-folder
/usr/share/emacs/site-lisp/vm/vm-virtual hides 
/usr/share/emacs/site-lisp/vm.in/vm-virtual
/usr/share/emacs/site-lisp/elpa/dash-2.17.0/dash hides 
/usr/share/emacs/site-lisp/elpa/dash-2.19.1/dash
/usr/share/emacs/site-lisp/elpa/dash-2.17.0/dash-autoloads hides 
/usr/share/emacs/site-lisp/elpa/dash-2.19.1/dash-autoloads
/usr/share/emacs/site-lisp/elpa/dash-2.17.0/dash-pkg hides 
/usr/share/emacs/site-lisp/elpa/dash-2.19.1/dash-pkg
/usr/share/emacs/site-lisp/elpa/seq-2.22/seq hides 
/usr/share/emacs/site-lisp/elpa/seq-2.23/seq
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/usr/share/emacs/site-lisp/elpa/slime-2.26.1/slime-autoloads hides 
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/usr/share/emacs/site-lisp/elpa/slime-2.26.1/slime hides 
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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 eieio eieio-core eieio-loaddefs
password-cache json map text-property-search time-date mm-decode
mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail comp comp-cstr subr-x rx cl-seq cl-macs cl-extra help-mode seq
seq-25 byte-opt gv warnings bytecomp byte-compile cconv rfc2047 rfc2045
ietf-drums mm-util mail-prsvr mail-utils cus-edit pp cus-start cus-load
wid-edit cl-loaddefs cl-lib vm-autoload vm-autoloads vm-version vm-vars
vm-init 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 lcms2
dynamic-setting system-font-setting font-render-setting cairo
move-toolbar gtk x-toolkit x multi-tty make-network-process
native-compile emacs)

Memory information:
((conses 16 133934 12639)
 (symbols 48 11016 1)
 (strings 32 31394 3667)
 (string-bytes 1 1130590)
 (vectors 16 19658)
 (vector-slots 8 370387 24015)
 (floats 8 39 31)
 (intervals 56 415 0)
 (buffers 992 14))