bug#42017: 26.3; format-mode-line and %p

[Humberto Sgrott Reis]

M-x ielm
> (setq mode-line-format "(%p)")
Hit enter numerous times to grow the buffer. The percentage will be
displayed with a percent sign at the end, and will be enclosed in parens.
> (setq mode-line-format (:eval (format-mode-line "(%p)")))
The percentage will be displayed without a percent sign at the end, and
the right paren will be overwritten.


In GNU Emacs 26.3 (build 1, x86_64-apple-darwin18.2.0, NS appkit-1671.20 
Version 10.14.3 (Build 18D109))
of 2019-09-02 built on builder10-14.porkrind.org
Windowing system distributor 'Apple', version 10.3.1894
Recent messages:
previous-line: Beginning of buffer [5 times]
next-line: End of buffer [6 times]
Print buffer *ielm*? n
ns-print-buffer: Canceled
funcall-interactively: End of buffer
next-line: End of buffer [6 times]
Quit
next-line: End of buffer [3 times]
Quit
mwheel-scroll: End of buffer
kill-region: Text is read-only: #<buffer *ielm*>
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 THREADS

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

Major mode: IELM

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 puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib 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 ielm easymenu pp comint
ansi-color ring elec-pair 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 threads kqueue cocoa ns multi-tty make-network-process emacs)

Memory information:
((conses 16 212685 10286)
(symbols 48 20424 2)
(miscs 40 58 195)
(strings 32 29932 2153)
(string-bytes 1 802080)
(vectors 16 35484)
(vector-slots 8 728369 10374)
(floats 8 50 272)
(intervals 56 609 0)
(buffers 992 12))