bug#23164: 25.1.50; xref-find-definitions with local tags-file-name fails

[Johan Claesson]

Hi,

emacs -Q 

(fundamental-mode)
(setq-local tags-file-name "/dev/zero")
(xref-find-definitions "foo")

Fails with (wrong-type-argument stringp nil) in
visit-tags-table-buffer.

The problem also occurs when tags-file-name points to a valid TAGS
file (the invalid /dev/zero was chosen just to make the recipe
short).

If tags-file-name have a global value there is no problem. 

It is the following line in visit-tags-table-buffer that fails. 

  (setq tags-file-name (tags-expand-table-name tags-file-name))

If this is protected with (when tags-file-name ...) then the problem
do not occur.  The same if the line is moved down and inside the
unless sexp that follows immediately.  If either is the right thing to
do i don't know.  But it seem a bit strange to assume that
tags-file-name shall be non-nil at that point.  The problem occurs
when etags--xref-find-definitions calls visit-tags-table-buffer for
the second time.

Regards,

/Johan



In GNU Emacs 25.1.50.1 (x86_64-unknown-linux-gnu, X toolkit)
 of 2016-03-28 built on goblin
Repository revision: a30e7e12ed8465e2565dd318d921bc87f52ce18e
Windowing system distributor 'The X.Org Foundation', version 11.0.11702000
System Description:     Ubuntu 15.10

Configured using:
 'configure --prefix=/ssd/home/jcl/usr --with-x-toolkit=lucid
 --without-toolkit-scroll-bars --disable-silent-rules
 --without-compress-install --enable-link-time-optimization
 PKG_CONFIG_PATH=/home/jcl/usr/lib/pkgconfig'

Configured features:
XAW3D XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF
GSETTINGS NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF
XFT ZLIB LUCID X11

Important settings:
  value of $LC_MONETARY: en_GB.UTF-8
  value of $LC_NUMERIC: en_GB.UTF-8
  value of $LC_TIME: en_GB.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: Text

Minor modes in effect:
  magit-auto-revert-mode: t
  display-time-mode: t
  minibuffer-depth-indicate-mode: t
  num3-mode: t
  minibuffer-electric-default-mode: t
  icomplete-mode: t
  diff-auto-refine-mode: t
  erc-list-mode: t
  erc-menu-mode: t
  erc-autojoin-mode: t
  erc-ring-mode: t
  erc-networks-mode: t
  erc-pcomplete-mode: t
  erc-track-mode: t
  erc-match-mode: t
  erc-button-mode: t
  erc-fill-mode: t
  erc-stamp-mode: t
  erc-netsplit-mode: t
  erc-irccontrols-mode: t
  erc-noncommands-mode: t
  erc-move-to-prompt-mode: t
  erc-readonly-mode: t
  global-git-commit-mode: t
  async-bytecomp-package-mode: t
  shell-dirtrack-mode: t
  wc-mode: t
  winner-mode: t
  ido-everywhere: t
  which-function-mode: t
  global-eldoc-mode: t
  electric-layout-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  global-prettify-symbols-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
  temp-buffer-resize-mode: t
  line-number-mode: t
  auto-fill-function: do-auto-fill
  transient-mark-mode: t
  abbrev-mode: t

Recent messages:
Saving file /home/jcl/.newsrc.eld...
Wrote /home/jcl/.newsrc.eld
Saving file /ssd/home/jcl/TAGS_REPORT...
Wrote /ssd/home/jcl/TAGS_REPORT
Preparing diary...done
Preparing diary...done
No event to add
Mark set [2 times]
Quit
Mark set

Load-path shadows:
None found.

Features:
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Memory information:
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