Subject: bug#29371: 26.0.50; (setf (buffer-modified-p) t) bug

From: Devon Sean McCullough <[email-masked]>
Date: Mon, 20 Nov 2017 20:53:02 -0500

(setf (buffer-modified-p) t) -> (with-current-buffer nil (set-buffer-modified-p t))
which bombs because nil is not a buffer.

Here's a fix:
diff -Bbdu old/cl-lib.el new/cl-lib.el
--- old/cl-lib.el	2017-06-06 16:19:10.000000000 -0400
+++ new/cl-lib.el	2017-11-20 20:08:41.000000000 -0500
@@ -539,7 +539,7 @@
 ;; Some more Emacs-related place types.
 (gv-define-simple-setter buffer-file-name set-visited-file-name t)
 (gv-define-setter buffer-modified-p (flag &optional buf)
-  `(with-current-buffer ,buf
+  `(with-current-buffer (or ,buf (current-buffer))
      (set-buffer-modified-p ,flag)))
 (gv-define-simple-setter buffer-name rename-buffer t)
 (gv-define-setter buffer-string (store)

		Peace
			--Devon

P.S. Here's a backtrace:
Debugger entered--Lisp error: (wrong-type-argument stringp nil)
  set-buffer(nil)
  (save-current-buffer (set-buffer nil) (set-buffer-modified-p t))
  (with-current-buffer nil (set-buffer-modified-p t))
  (setf (buffer-modified-p) t)
  eval((setf (buffer-modified-p) t))
  command-line-1(("--funcall" "toggle-debug-on-error" "--load" "cl" "--eval" "(setf (buffer-modified-p) t)"))
  command-line()
  normal-top-level()

P.P.S. We can imagine optimizers
which know (or nil ...) -> (or ...), (or #) -> #
and (with-current-buffer (current-buffer) ...) -> (progn ...)
but this is, after all, simply a text editor.

In GNU Emacs 26.0.50 (build 1, x86_64-apple-darwin13.4.0, NS appkit-1265.21 Version 10.9.5 (Build 13F1911))
 of 2017-06-07 built on builder10-9.local
Windowing system distributor 'Apple', version 10.3.1404
Recent messages:
Warning: arch-dependent data dir ’/Users/build/workspace/Emacs-Multi-Build/label/mavericks/emacs-source/nextstep/Emacs.app/Contents/MacOS/libexec/’: No such file or directory

For information about GNU Emacs and the GNU system, type C-h C-a.
Debug on Error enabled globally
Entering debugger...

Configured using:
 'configure --with-ns '--enable-locallisppath=/Library/Application
 Support/Emacs/${version}/site-lisp:/Library/Application
 Support/Emacs/site-lisp' --with-modules'

Configured features:
NOTIFY ACL GNUTLS LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Debugger

Minor modes in effect:
  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

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message subr-x puny seq byte-opt
bytecomp byte-compile cconv dired dired-loaddefs format-spec rfc822 mml
mml-sec password-cache epa derived epg epg-config gnus-util rmail
rmail-loaddefs mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils help-mode easymenu debug cl gv cl-loaddefs
cl-lib cus-start cus-load time-date tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/ns-win ns-win
ucs-normalize mule-util term/common-win 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 kqueue cocoa ns multi-tty make-network-process emacs)

Memory information:
((conses 16 213089 10429)
 (symbols 48 21048 2)
 (miscs 40 64 182)
 (strings 32 20087 5364)
 (string-bytes 1 619310)
 (vectors 16 35085)
 (vector-slots 8 697226 6051)
 (floats 8 54 126)
 (intervals 56 252 0)
 (buffers 976 12))