bug#36396: 27.0.50; rx-to-string fails: wrong-type-argument characterp "\\(?"

[Göktuğ Kayaalp]

I started encountering this after building
"260b6c2c931d74ef64dacb20b7fcae6f888e6d42" today.

Eval the following with debugging enabled (taken from magit-todos.el,
just the outer let form added).  Results in the error mentioned in the
subject.

(let ((keywords (list "a" "b"))
      (magit-todos-keyword-suffix "\\(?:([^)]+)\\)?:"))
 (rx-to-string
  `(seq bol
        ;; Filename
        (group-n 8 (1+ (not (any ":")))) ":"
        ;; Line
        (group-n 2 (1+ digit)) ":"
        (or
         ;; Org item
         (seq (group-n 1 (1+ "*"))
              (1+ blank)
              (group-n 4 (or ,@keywords))
              (1+ blank)
              (group-n 5 (1+ not-newline)))
         ;; Non-Org
         (seq (optional (1+ not-newline))
              (group-n 4 (or ,@keywords))
              (optional (group-n 6 (regexp ,magit-todos-keyword-suffix)))
              (optional (1+ blank))
              (optional (group-n 5 (1+ not-newline))))))))

Excerpt from the backtrace:

Debugger entered--Lisp error: (wrong-type-argument characterp "\\(?")
  mapconcat(identity ("\\(?:.+\\)?" "\\(?4:[ab]\\)" ("\\(?" "6" ":" "\\)" "?") 
"\\(?:[[:blank:]]+\\)?" "\\(?5:.+\\)?") nil)
  rx--subforms(((optional (1+ not-newline)) (group-n 4 (or "a" "b")) (optional 
(group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional (1+ blank)) (optional 
(group-n 5 (1+ not-newline)))) :)
  rx-and((seq (optional (1+ not-newline)) (group-n 4 (or "a" "b")) (optional 
(group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional (1+ blank)) (optional 
(group-n 5 (1+ not-newline)))))
  rx-form((seq (optional (1+ not-newline)) (group-n 4 (or "a" "b")) (optional 
(group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional (1+ blank)) (optional 
(group-n 5 (1+ not-newline)))) |)
  #f(compiled-function (x) #<bytecode 0x15683f299d61>)((seq (optional (1+ 
not-newline)) (group-n 4 (or "a" "b")) (optional (group-n 6 (regexp 
"\\(?:([^)]+)\\)?:"))) (optional (1+ blank)) (optional (group-n 5 (1+ 
not-newline)))))
  mapcar(#f(compiled-function (x) #<bytecode 0x15683f299d61>) ((seq (group-n 1 
(1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ blank) (group-n 5 (1+ 
not-newline))) (seq (optional (1+ not-newline)) (group-n 4 (or "a" "b")) 
(optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional (1+ blank)) 
(optional (group-n 5 (1+ not-newline))))))
  rx--subforms(((seq (group-n 1 (1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) 
(1+ blank) (group-n 5 (1+ not-newline))) (seq (optional (1+ not-newline)) 
(group-n 4 (or "a" "b")) (optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) 
(optional (1+ blank)) (optional (group-n 5 (1+ not-newline))))) | "\\|")
  rx-or((or (seq (group-n 1 (1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ 
blank) (group-n 5 (1+ not-newline))) (seq (optional (1+ not-newline)) (group-n 
4 (or "a" "b")) (optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional 
(1+ blank)) (optional (group-n 5 (1+ not-newline))))))
  rx-form((or (seq (group-n 1 (1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ 
blank) (group-n 5 (1+ not-newline))) (seq (optional (1+ not-newline)) (group-n 
4 (or "a" "b")) (optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional 
(1+ blank)) (optional (group-n 5 (1+ not-newline))))) :)
  #f(compiled-function (x) #<bytecode 0x15683f299d29>)((or (seq (group-n 1 (1+ 
"*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ blank) (group-n 5 (1+ 
not-newline))) (seq (optional (1+ not-newline)) (group-n 4 (or "a" "b")) 
(optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional (1+ blank)) 
(optional (group-n 5 (1+ not-newline))))))
  mapcar(#f(compiled-function (x) #<bytecode 0x15683f299d29>) (bol (group-n 8 
(1+ (not (any ":")))) ":" (group-n 2 (1+ digit)) ":" (or (seq (group-n 1 (1+ 
"*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ blank) (group-n 5 (1+ 
not-newline))) (seq (optional (1+ not-newline)) (group-n 4 (or "a" "b")) 
(optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional (1+ blank)) 
(optional (group-n 5 (1+ not-newline)))))))
  rx--subforms((bol (group-n 8 (1+ (not (any ":")))) ":" (group-n 2 (1+ digit)) 
":" (or (seq (group-n 1 (1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ 
blank) (group-n 5 (1+ not-newline))) (seq (optional (1+ not-newline)) (group-n 
4 (or "a" "b")) (optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional 
(1+ blank)) (optional (group-n 5 (1+ not-newline)))))) :)
  rx-and((seq bol (group-n 8 (1+ (not (any ":")))) ":" (group-n 2 (1+ digit)) 
":" (or (seq (group-n 1 (1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ 
blank) (group-n 5 (1+ not-newline))) (seq (optional (1+ not-newline)) (group-n 
4 (or "a" "b")) (optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional 
(1+ blank)) (optional (group-n 5 (1+ not-newline)))))))
  rx-form((seq bol (group-n 8 (1+ (not (any ":")))) ":" (group-n 2 (1+ digit)) 
":" (or (seq (group-n 1 (1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) (1+ 
blank) (group-n 5 (1+ not-newline))) (seq (optional (1+ not-newline)) (group-n 
4 (or "a" "b")) (optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) (optional 
(1+ blank)) (optional (group-n 5 (1+ not-newline)))))))
  rx-to-string((seq bol (group-n 8 (1+ (not (any ":")))) ":" (group-n 2 (1+ 
digit)) ":" (or (seq (group-n 1 (1+ "*")) (1+ blank) (group-n 4 (or "a" "b")) 
(1+ blank) (group-n 5 (1+ not-newline))) (seq (optional (1+ not-newline)) 
(group-n 4 (or "a" "b")) (optional (group-n 6 (regexp "\\(?:([^)]+)\\)?:"))) 
(optional (1+ blank)) (optional (group-n 5 (1+ not-newline)))))))
  (let ((keywords (list "a" "b")) (magit-todos-keyword-suffix 
"\\(?:([^)]+)\\)?:")) (rx-to-string (list 'seq 'bol '(group-n 8 (1+ (not (any 
":")))) ":" '(group-n 2 (1+ digit)) ":" (list 'or (cons 'seq (cons '(group-n 1 
...) (cons '... (cons ... ...)))) (cons 'seq (cons '(optional ...) (cons (list 
... 4 ...) (cons ... ...))))))))
  eval-region(146 853 t #f(compiled-function (ignore) #<bytecode 
0x15683f299ced>))  ; Reading at buffer position 853
  elisp--eval-defun()
  eval-defun(nil)
  funcall-interactively(eval-defun nil)
  call-interactively(eval-defun nil nil)
  command-execute(eval-defun)




In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5, cairo 
version 1.16.0)
 of 2019-06-26 built on alpha
Repository revision: 260b6c2c931d74ef64dacb20b7fcae6f888e6d42
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description: Debian GNU/Linux 10 (buster)

Recent messages:
~/cf/emacs.d/lisp/site 
~/cf/emacs.d/lisp 
~/cf/emacs.d 
~/cf 
rx--subforms: Wrong type argument: characterp, "\\(?" [2 times]
Debug on Error enabled globally
Debug on Quit enabled globally
Entering debugger...
Quit
user-error: Previous command was not a yank

Configured using:
 'configure --prefix=/home/g/local/emacs --with-x-toolkit=gtk3
 --with-modules --with-file-notification=yes --with-gameuser=no
 --with-cairo --with-mailutils'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD
JSON PDUMPER LCMS2 GMP

Important settings:
  value of $LC_MONETARY: tr_TR.UTF-8
  value of $LC_TIME: tr_TR.UTF-8
  value of $LANG: en_GB.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Debugger

Minor modes in effect:
  auto-image-file-mode: t
  show-paren-mode: t
  gk-ucins-entry-mode: t
  global-gk-minor-mode: t
  gk-minor-mode: t
  yas-global-mode: t
  yas-minor-mode: t
  winner-mode: t
  global-whitespace-mode: t
  which-key-mode: t
  save-place-mode: t
  persistent-scratch-autosave-mode: t
  global-paren-face-mode: t
  magit-todos-mode: t
  global-magit-file-mode: t
  url-handler-mode: t
  global-git-commit-mode: t
  shell-dirtrack-mode: t
  eval-sexp-fu-flash-mode: t
  auto-insert-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-quote-mode: t
  mouse-wheel-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 mailalias mail-extr emacsbug cl-print pcmpl-unix
bug-reference dired-aux dabbrev two-column iso-transl rmailout qp
executable rmailmm misearch multi-isearch eieio-opt speedbar sb-image
ezimage dframe help-fns radix-tree vc-filewise diary-lib diary-loaddefs
cal-iso image-file paren paper-theme init gk-feeds man org-rmail org-mhe
org-irc org-info org-gnus nnir gnus-sum gnus-group gnus-undo gnus-start
gnus-cloud nnimap utf7 gnus-spec gnus-win org-docview org-bibtex bibtex
org-bbdb org-w3m loadhist ob-python ob-shell yasnippet elec-pair
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wdired vc-rcs vc-cvs vc vc-dispatcher turkish tramp-cache time thinks
smtpmail sendmail scheme saveplace rmailsum python tramp-sh tramp
tramp-loaddefs trampver tramp-integration files-x tramp-compat
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elfeed-lib url-util time-date avl-tree generator url-queue url-parse
url-vars xml-query xml dollar doc-view jka-compr image-mode dired-x
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crm mailabbrev vcard bbdb derived easymenu bbdb-site timezone autoinsert
auth-source eieio eieio-core eieio-loaddefs password-cache json subr-x
map seq byte-opt bytecomp byte-compile cconv apropos ansi-color
ace-jump-mode advice cl-macs cl gv cl-seq 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
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backquote threads dbusbind inotify lcms2 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 990275 71274)
 (symbols 48 50169 30)
 (strings 32 169409 11941)
 (string-bytes 1 5711072)
 (vectors 16 91201)
 (vector-slots 8 1897909 201284)
 (floats 8 779 284)
 (intervals 56 13672 1432)
 (buffers 992 61))

-- 
İ. Göktuğ Kayaalp       <https://www.gkayaalp.com/>
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