bug#49746: 28.0.50; bytecompilation introduces bug in org-capture with certain template

[Gregor Zattler]

Dear emacs developers, I use org-capture a lot with
org-capture-templates. It stopped working a few days ago,
throwing a error message instead:

org-capture: Capture abort: Unknown template placeholder: "%^g"

This is due to a problem with byte compilation.  It does not
happen, if I remove all .elc files before starting emacs.


You may test it with this:

(custom-set-variables
 '(org-capture-templates '(("d" "diary" entry (file "~/notes.org") "*** %? 
%^g"))))


in   minconfig.el   and with this invocation of emacs:

~/src/emacs$ src/emacs -Q -l /tmp/minconfig.el --eval '(org-capture 0 "d")'

If this gives you an error, quit emacs, remove all .elc
-files:

~/src/emacs$ find -type f -print0| grep -zZ "\.elc$" |xargs -0r rm

start emacs again:

~/src/emacs$ src/emacs -Q -l /tmp/minconfig.el --eval '(org-capture 0 "d")'

and there is no error.



I narrowed it down to this commit:


51a86b6a0504d580d3e10efe41abf3ae42c90711 is the first bad commit
commit 51a86b6a0504d580d3e10efe41abf3ae42c90711
Author: Mattias Engdegård <mattiase@acm.org>
Date:   Tue Jul 20 17:23:11 2021 +0200

    Count (not X) as a switch condition

    * lisp/emacs-lisp/bytecomp.el (byte-compile--cond-switch-prefix):
    Treat (not VAR) and (null VAR) as (eq VAR nil) when computing the
    extent of switch ops.

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 6970c8a5055..2968f1af5df 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -4340,6 +4340,16 @@ byte-compile--cond-switch-prefix
                          (push value keys)
                          (push (cons (list value) (or body '(t))) cases))
                        t))))
+             ;; Treat (not X) as (eq X nil).
+             (`((,(or 'not 'null) ,(and var (pred symbolp))) . ,body)
+              (and (or (eq var switch-var) (not switch-var))
+                   (progn
+                     (setq switch-var var)
+                     (setq switch-test 'eq)
+                     (unless (memq nil keys)
+                       (push nil keys)
+                       (push (cons (list nil) (or body '(t))) cases))
+                     t)))
              (`((,(and fn (or 'memq 'memql 'member)) ,var ,expr) . ,body)
               (and (symbolp var)
                    (or (eq var switch-var) (not switch-var))

:040000 040000 ae3e2ceaa690965108fb8547ce6e90ecd2fcaaf3 
28eec9e6920160dc5dff29e2567ee34b50924bec M      lisp


The problem came up recently on the org-mode mailing list:
https://www.mail-archive.com/emacs-orgmode@gnu.org/msg138065.html
Especially this message:
https://www.mail-archive.com/emacs-orgmode@gnu.org/msg138121.html
inspired me to do a git bisect and test builds if the throw
this error and if so, if it also happens after removing all
.elc files.

For every step in git bisect I did a

rm -rf * ; git checkout -f ; make 

in order to make sure that all .elc files are build afresh.


Ciao; Gregor
-- 
 -... --- .-. . -.. ..--.. ...-.-