bug#23949: 25.0.95; Regression in handling error caused by (string-match-p "." nil)

[Kaushal Modi]

As I do not understand the true nature of this bug, the title of this debbugs could be confusing. Please read the below in entirety.

Related discussion is also on emacs-devel: https://lists.gnu.org/archive/html/emacs-devel/2016-07/msg00519.html

Evaluating the below in emacs 24.5 emacs -Q results in the below error backtrace as expected:

=====

Debugger entered--Lisp error: (wrong-type-argument stringp nil)

  string-match("." nil nil)

  string-match-p("." nil)

  (progn (require (quote package)) (if (member (quote ("melpa" . "http://melpa.org/packages/")) package-archives) package-archives (setq package-archives (append package-archives (list (quote ("melpa" . "http://melpa.org/packages/")))))) (package-initialize) (package-refresh-contents) (package-install (quote projectile)) (require (quote projectile)) (projectile-global-mode) (string-match-p "." nil))

  eval((progn (require (quote package)) (if (member (quote ("melpa" . "http://melpa.org/packages/")) package-archives) package-archives (setq package-archives (append package-archives (list (quote ("melpa" . "http://melpa.org/packages/")))))) (package-initialize) (package-refresh-contents) (package-install (quote projectile)) (require (quote projectile)) (projectile-global-mode) (string-match-p "." nil)) nil)

  eval-last-sexp-1(nil)

  eval-last-sexp(nil)

  call-interactively(eval-last-sexp nil nil)

  command-execute(eval-last-sexp)

=====

Minimal code to reproduce the issue:

=====

(progn

  (require 'package)

  (add-to-list 'package-archives '("melpa" . "http://melpa.org/packages/") t)

  (package-initialize)

  (package-refresh-contents)

  (package-install 'projectile)

  (require 'projectile)

  (projectile-global-mode)

  (string-match-p "." nil))

=====

But evaluating the same on emacs-25 build results in:

=====

Entering debugger...

help-function-arglist: End of file during parsing

=====

Also evaluating the above after M-x toggle-debug-on-error does not give a backtrace on the "help-function-arglist: End of file during parsing" error.

This is a regression from how the actual error (wrong-type-argument stringp nil) backtrace showed up correctly on emacs 24.5 but is giving confusing and difficult to debug error on emacs-25.

emacs-25 build info:

In GNU Emacs 25.0.95.11 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.23)

 of 2016-06-29 built on ulcf41.cld.analog.com

Repository revision: 6192b6c3a4374b2cb6e02ca865e1899a04a7f7dc

Windowing system distributor 'The X.Org Foundation', version 11.0.60900000

System Description: Red Hat Enterprise Linux Workstation release 6.6 (Santiago)

Configured using:

 'configure --with-modules

 --prefix=/home/kmodi/usr_local/apps/6/emacs/emacs-25

 'CPPFLAGS=-fgnu89-inline -I/home/kmodi/usr_local/6/include

 -I/usr/include/freetype2 -I/usr/include' 'CFLAGS=-ggdb3 -O0'

 'CXXFLAGS=-ggdb3 -O0' 'LDFLAGS=-L/home/kmodi/usr_local/6/lib

 -L/home/kmodi/usr_local/6/lib64 -ggdb3'

 PKG_CONFIG_PATH=/home/kmodi/usr_local/6/lib/pkgconfig:/home/kmodi/usr_local/6/lib64/pkgconfig:/cad/adi/apps/gnu/linux/x86_64/6/lib/pkgconfig:/cad/adi/apps/gnu/linux/x86_64/6/lib64/pkgconfig:/usr/lib/pkgconfig:/usr/lib64/pkgconfig:/usr/share/pkgconfig:/lib/pkgconfig:/lib64/pkgconfig'

Configured features:

XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GCONF GSETTINGS

NOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE LIBOTF XFT ZLIB

TOOLKIT_SCROLL_BARS GTK2 X11 MODULES

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Kaushal Modi