bug#46122: 25.2; changes to .dir-locals.el are not picked up when .dir-locals.el is a symlink

[Dan Connolly]

1. Create ~/projects/m/.dir-locals.el file to set tab-width to 4.
2. Visit ~/projects/m/xyz.c and verify that tabs use 4 spaces
3. mv ~/projects/m/.dir-locals.el to ~/.emacs.d/m-locals.el
4. ln -s ~/.emacs.d/m-locals.el ~/projects/m/.dir-locals.el
5. Change 4 6 in ~/.emacs.d/m-locals.el
6. in the xyz.c buffer, M-x revert-buffer

expected result:
7. tabs use 6 spaces

actual result:
7. no change; tabs still use 4 spaces

work-around:
(setq dir-locals-directory-cache nil) before step 6.




In GNU Emacs 25.2.2 (x86_64-pc-linux-gnu, GTK+ Version 3.22.21)
 of 2017-09-22, modified by Debian built on lgw01-amd64-050
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Ubuntu 18.04.5 LTS

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 --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --build x86_64-linux-gnu
 --prefix=/usr --sharedstatedir=/var/lib --libexecdir=/usr/lib
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-pop=yes
 
--enable-locallisppath=/etc/emacs25:/etc/emacs:/usr/local/share/emacs/25.2/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/25.2/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-x=yes --with-x-toolkit=gtk3
 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
 -fdebug-prefix-map=/build/emacs25-jYekUr/emacs25-25.2+1=.
-fstack-protector-strong
 -Wformat -Werror=format-security -Wall' 'CPPFLAGS=-Wdate-time
 -D_FORTIFY_SOURCE=2' 'LDFLAGS=-Wl,-Bsymbolic-functions -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

Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

Major mode: Magit

Minor modes in effect:
  diff-auto-refine-mode: t
  magit-auto-revert-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  shell-dirtrack-mode: t
  direnv-mode: t
  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
  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

Recent messages:
Mark set
Press C-c C-c when you are done editing.
Enter a change comment.  Type C-c C-c when done
Checking in 
/home/connolly/projects/emacs-dotfiles/moddable-c-style/.dir-locals.el...done
[C-t] show common commands, [?] describe events, [C-h i] show manual [2 times]
Running git push -v dckc master:refs/heads/master
Git finished
mwheel-scroll: Beginning of buffer
mwheel-scroll: End of buffer
mwheel-scroll: Beginning of buffer

Load-path shadows:
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Features:
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server shell pcomplete comint ansi-color dired js-dev-flow
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hashtable-print-readable backquote dbusbind inotify dynamic-setting
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multi-tty make-network-process emacs)

Memory information:
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 (symbols 48 39612 1)
 (miscs 40 1701 1142)
 (strings 32 103022 8981)
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