bug#39971: 28.0.50; Behavior change in flymake-diagnostic-beg/end

[Philipp Stephani]

With Emacs 26:

$ emacs -Q -batch -l flymake --eval='(with-temp-buffer (let ((debug-on-error t) 
(diag (flymake-make-diagnostic (current-buffer) 1 1 (quote warning) "foo"))) 
(print (flymake-diagnostic-beg diag))))'

1

With the Emacs 27 pretest:

$ ./src/emacs -Q -batch -l flymake --eval='(with-temp-buffer (let 
((debug-on-error t) (diag (flymake-make-diagnostic (current-buffer) 1 1 (quote 
warning) "foo"))) (print (flymake-diagnostic-beg diag))))'
Debugger entered--Lisp error: (wrong-type-argument overlayp nil)
  overlay-start(nil)
  flymake-diagnostic-beg(#s(flymake--diag :buffer #<buffer  *temp*> :beg 1 :end 
1 :type warning :text "foo" :backend nil :data nil :overlay-properties nil 
:overlay nil))
[…]

This was introduced in commit 5b48dab412c61980bca63a67a5d548d07e56b404.
While the intention of that commit is good, I'm not sure we should make
such a breaking change.  Basically, the flymake-diagnostic type no
longer behaves like an ordinary struct.


In GNU Emacs 28.0.50 (build 10, x86_64-pc-linux-gnu, GTK+ Version 3.24.12, 
cairo version 1.16.0)
 of 2020-02-25
Repository revision: 03c07c88d90b5747456b9d286bace2dd4a713aac
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux rodete

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.

Configured using:
 'configure --enable-gcc-warnings=warn-only
 --enable-gtk-deprecation-warnings --without-pop --with-mailutils
 --enable-checking --enable-check-lisp-object-type --with-modules
 'CFLAGS=-O0 -ggdb3''

Configured features:
XPM JPEG TIFF GIF PNG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS FREETYPE HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS GTK3 X11
XDBE XIM MODULES THREADS PDUMPER GMP

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

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  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
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec epa epg epg-config gnus-util
rmail rmail-loaddefs text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils phst skeleton
derived edmacro kmacro pcase ffap thingatpt url-parse auth-source cl-seq
eieio eieio-core cl-macs eieio-loaddefs password-cache json map url-vars
subr-x rx gnutls puny seq byte-opt gv bytecomp byte-compile cconv dbus
xml cl-loaddefs cl-lib 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
tab-bar menu-bar rfn-eshadow isearch timer select scroll-bar mouse
jit-lock font-lock syntax facemenu font-core term/tty-colors frame
minibuffer 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 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 cairo move-toolbar gtk x-toolkit x multi-tty
make-network-process emacs)

Memory information:
((conses 16 59428 8101)
 (symbols 48 8079 1)
 (strings 32 20894 1798)
 (string-bytes 1 679977)
 (vectors 16 12054)
 (vector-slots 8 164864 5040)
 (floats 8 26 33)
 (intervals 56 196 0)
 (buffers 1000 11))