bug#15577: 24.3; dir-local variables not applied when switching major-mode

[yary]

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Please describe exactly what actions triggered the bug, and
the precise symptoms of the bug.  If you can, give a recipe
starting from `emacs -Q':

If I create a ".dir-locals.el" that applies to all major modes, such as:
  ((nil . ((tab-width . 3))))
It works when first opening any file under that directory- good. But, if
I switch the buffer's major-mode, it loses the directory-local
tab-width - and I've seen it lose other variables as well.

An alternate case showing the same is to have a ".dir-locals.el" like:
  ((js-mode . ((tab-width . 3))))

and opening a non-JS file in the directory, such as an HTML file, and
then switching to js-mode. Since I'm now editing the file in js-mode,
I would want it to read the js-mode dir-local variables.

Losing dir-locals seems like a bug to me, though perhaps there is a
reason for it. I did notice from other dir-local-related bugs that
they require some
thought as to how to handle edge cases...



In GNU Emacs 24.3.1 (i386-mingw-nt5.1.2600)
 of 2013-03-17 on MARVIN
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include
 -ID:/devel/emacs/libs/libiconv-1.13.1-1-dev/include
 -ID:/devel/emacs/libs/libxml2-2.7.8/include/libxml2'

Important settings:
  value of $LANG: ENU
  locale-coding-system: cp1252
  default enable-multibyte-characters: t

Major mode: Info

Minor modes in effect:
  yas-global-mode: t
  yas-minor-mode: t
  global-auto-complete-mode: t
  diff-auto-refine-mode: t
  recentf-mode: t
  desktop-save-mode: t
  tooltip-mode: t
  mouse-wheel-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

Features:
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mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader
sendmail rfc2047 rfc2045 ietf-drums conf-mode sh-script smie executable
info dos org-table org-wl org-w3m org-vm org-rmail org-mhe org-mew
org-irc org-jsinfo org-infojs org-html org-exp ob-exp org-exp-blocks
org-agenda org-info org-gnus org-docview org-bibtex bibtex org-bbdb
face-remap gtags js json moz imenu thingatpt vc-git js2-mode-autoloads
finder-inf undo-tree-autoloads package multi-web-mode mumamo-fun
mumamo-chunks amrita desktop-autosave hide-lines yasnippet help-mode
auto-complete-config auto-complete popup flymake-jslint flymake php-mode
etags cc-langs cc-mode cc-fonts cc-guess cc-menus cc-cmds cc-styles
cc-align speedbar sb-image ezimage dframe psvn derived log-edit
pcvs-util add-log diff-mode elp ediff-merg ediff-diff ediff-wind
ediff-mult ediff-help ediff-init ediff-util dired emacsw32 w32-integ
w32shell w32-grep rebind ourcomments-widgets ourcomments-util rx
cus-edit cus-start cus-load uniquify recentf tree-widget mm-url url
url-proxy url-privacy url-expand url-methods url-history url-cookie
url-domsuf url-util url-parse auth-source eieio password-cache url-vars
mailcap gnus gnus-ems nnheader gnus-util mail-utils mm-util mail-prsvr
org ob-tangle ob-ref ob-lob ob-table org-footnote org-src ob-comint
ob-keys org-pcomplete pcomplete org-list org-faces org-entities noutline
outline org-version ob-emacs-lisp ob org-compat org-macs ob-eval
org-loaddefs format-spec find-func cal-menu calendar cal-loaddefs ido
grep compile comint ansi-color ring bookmark pp apropos mumamo byte-opt
warnings bytecomp byte-compile cconv advice help-fns advice-preload
sgml-mode ruby-mode rng-nxml rng-valid rng-loc rng-uri rng-parse
nxml-parse rng-match rng-dt rng-util rng-pttrn nxml-ns nxml-mode
nxml-outln nxml-rap nxml-util nxml-glyph nxml-enc xmltok mumamo-cmirr
flyspell ispell desktop cc-engine cc-vars cc-defs new-key-seq-widget
edmacro kmacro wid-edit hfyview easy-mmode easymenu htmlfontify cl-macs
gv cl cl-lib noprint nxhtml-loader emacsw32-eol time-date tooltip
ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp
w32-common-fns disp-table w32-win w32-vars tool-bar dnd fontset image
regexp-opt fringe tabulated-list newcomment lisp-mode register page
menu-bar rfn-eshadow timer select scroll-bar mouse jit-lock font-lock
syntax facemenu font-core frame cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese hebrew greek
romanian slovak czech european ethiopic indian cyrillic chinese
case-table epa-hook jka-cmpr-hook help simple abbrev minibuffer loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote make-network-process w32 multi-tty emacs)