bug#38777: 26.3; tar-mode doesn't list a file / crashes on package-tar-file-info

[Victor Collod]

Hello!

A few months ago, the nix port of irony stopped building for a very, very 
strange reason:
when the complete path of the package metadata file is 32 characters long (plus 
some other unknown conditions), it isn't shown in the tar-mode file list view, 
and running (package-tar-file-info) fails with the following stack trace:

> Debugger entered--Lisp error: (wrong-type-argument arrayp nil)
>   tar--describe-as-link(nil)
>   tar--check-descriptor(nil)
>   tar-get-file-descriptor("irony-20190703.1732/irony-pkg.el")
>   package-tar-file-info()
>   eval((package-tar-file-info) nil)
>   eval-expression((package-tar-file-info) nil nil 127)
>   funcall-interactively(eval-expression (package-tar-file-info) nil nil 127)
>   call-interactively(eval-expression record nil)
>   command-execute(eval-expression record)
>   execute-extended-command(nil "eval-expression" nil)
>   funcall-interactively(execute-extended-command nil "eval-expression" nil)
>   call-interactively(execute-extended-command nil nil)
>   command-execute(execute-extended-command)

Unfortunately, my yet to be found lisp programming skills are way too low to 
solve this issue.
I have tried and failed to understand what's going on. Perhaps this bug isn't a 
good introduction to lisp programming :/

Here is the related (worked around) NixOS issue:
https://github.com/NixOS/nixpkgs/issues/66556#issuecomment-522809883

And a link to a zip file containing the cursed tar file:
https://github.com/NixOS/nixpkgs/files/3522572/repro.zip


Configured using:
 'configure
 --prefix=/nix/store/bgv2mpq96crnldxkq79iwc31qadnq5al-emacs-26.3
 --disable-build-details --with-modules --with-x-toolkit=gtk3 --with-xft
 CFLAGS=-DMAC_OS_X_VERSION_MAX_ALLOWED=101200'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS GLIB NOTIFY LIBSELINUX
GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB TOOLKIT_SCROLL_BARS
GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD

Important settings:
  value of $EMACSLOADPATH: 
/nix/store/62ynkkg5w0c1kxwlxdwzcvja47wmxycl-emacs-packages-deps/share/emacs/site-lisp:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Debugger

Minor modes in effect:
  shell-dirtrack-mode: t
  global-whitespace-mode: t
  which-key-mode: t
  editorconfig-mode: t
  diff-auto-refine-mode: t
  show-paren-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-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
  buffer-read-only: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/home/multun/.nix-profile/share/emacs/site-lisp/git hides 
/run/current-system/sw/share/emacs/site-lisp/git
/home/multun/.nix-profile/share/emacs/site-lisp/git-blame hides 
/run/current-system/sw/share/emacs/site-lisp/git-blame
/run/current-system/sw/share/emacs/site-lisp/site-start hides 
/nix/store/62ynkkg5w0c1kxwlxdwzcvja47wmxycl-emacs-packages-deps/share/emacs/site-lisp/site-start
/run/current-system/sw/share/emacs/site-lisp/site-start hides 
/nix/store/bgv2mpq96crnldxkq79iwc31qadnq5al-emacs-26.3/share/emacs/site-lisp/site-start
/nix/store/62ynkkg5w0c1kxwlxdwzcvja47wmxycl-emacs-packages-deps/share/emacs/site-lisp/elpa/seq-2.20/seq
 hides 
/nix/store/bgv2mpq96crnldxkq79iwc31qadnq5al-emacs-26.3/share/emacs/26.3/lisp/emacs-lisp/seq
/nix/store/62ynkkg5w0c1kxwlxdwzcvja47wmxycl-emacs-packages-deps/share/emacs/site-lisp/elpa/let-alist-1.0.6/let-alist
 hides 
/nix/store/bgv2mpq96crnldxkq79iwc31qadnq5al-emacs-26.3/share/emacs/26.3/lisp/emacs-lisp/let-alist

Features:
(cl-print debug shadow sort company-oddmuse company-keywords
company-etags etags company-gtags company-dabbrev-code company-dabbrev
company-files company-capf company-cmake company-xcode company-clang
company-semantic company-eclim company-bbdb company-irony
company-template company pcase mail-extr tar-mode arc-mode archive-mode
emacsbug yaml-mode diff novice xref project vc vc-dispatcher smerge-mode
js sgml-mode dom imenu rst compile writeroom-mode visual-fill-column
dired-aux face-remap nix-mode ffap nix-repl nix-shell nix-store
nix-instantiate nix-shebang nix-format nix markdown-mode color noutline
outline python tramp-sh tramp tramp-compat tramp-loaddefs trampver
ucs-normalize shell pcomplete parse-time comint ring ansi-color
make-mode two-column iso-transl sendmail misearch multi-isearch lisp-mnt
irony-cdb-libclang irony-cdb-json pp irony-cdb-clang-complete irony-cdb
irony-completion irony-snippet flycheck-irony irony-diagnostics irony
irony-iotask flycheck cl-extra json map find-func help-mode rx subr-x
dash cc-mode cc-fonts cc-guess cc-menus cc-cmds cc-styles cc-align
cc-engine cc-vars cc-defs vc-git sh-script smie executable server
elec-pair multiple-cursors mc-hide-unmatched-lines-mode
mc-separate-operations rectangular-region-mode mc-mark-pop mc-mark-more
mc-cycle-cursors mc-edit-lines multiple-cursors-core rect clang-format
xml whitespace rainbow-delimiters which-key editorconfig notmuch hl-line
notmuch-hello wid-edit notmuch-tree notmuch-show notmuch-print
notmuch-crypto notmuch-mua notmuch-message notmuch-draft
notmuch-maildir-fcc notmuch-address notmuch-company notmuch-parser
notmuch-wash diff-mode easy-mmode coolj notmuch-query goto-addr
thingatpt icalendar diary-lib diary-loaddefs cal-menu calendar
cal-loaddefs notmuch-tag edmacro kmacro crm notmuch-lib advice
notmuch-version notmuch-compat cl message rmc puny dired dired-loaddefs
format-spec rfc822 mml mailabbrev gmm-utils mailheader mm-view mml-smime
mml-sec epa derived epg gnus-util rmail rmail-loaddefs mail-utils smime
dig mm-decode mm-bodies mm-encode mailcap mail-parse rfc2231 rfc2047
rfc2045 mm-util ietf-drums mail-prsvr time-date tsdh-dark-theme paren
cus-start cus-load finder-inf info package easymenu epg-config
url-handlers url-parse auth-source cl-seq eieio eieio-core cl-macs
eieio-loaddefs password-cache url-vars seq seq-25 byte-opt gv bytecomp
byte-compile cconv cl-loaddefs cl-lib mule-util tooltip eldoc electric
uniquify ediff-hook vc-hooks lisp-float-type 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 elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame 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 charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads dbusbind inotify dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 813410 99456)
 (symbols 48 53733 20)
 (miscs 40 4416 6082)
 (strings 32 159751 8703)
 (string-bytes 1 4644355)
 (vectors 16 74595)
 (vector-slots 8 2364846 103216)
 (floats 8 328 893)
 (intervals 56 71244 222)
 (buffers 992 99))

-- 
Victor Collod