Subject: 30.0.50; byte-compile-preprocess mutates self evaluating forms in expanded macro bodies

From: Vibhav Pant <[email-masked]>
Date: Sat, 21 Jan 2023 02:54:05 +0530

`cconv-closure-convert`, called from `byte-compile-preprocess` calls
`setcar` on a self evaluating interactive form as part of the function
body. This can be reproduced by adding the following snippet to
`lisp/loadup.el`, and building Emacs:

```
(load "emacs-lisp/bytecomp")
(setq sample-interactive-spec
      (purecopy '(interactive
                  (list (if current-prefix-arg
                            (prefix-numeric-value 
                             current-prefix-arg)
                          'toggle)))))

(defmacro define-purecopied-func ()
  `(defun foo-bar (arg)
     ,sample-interactive-spec))

(let ((byte-compile-debug t))
  (byte-compile '(define-purecopied-func)))
```
(`purecopy` ensures mutating the list triggers a `pure_write_error`)

As mutating quoted/constant lists is undefined behaviour as per the
Elisp reference manual
(https://www.gnu.org/software/emacs/manual/html_node/elisp/Mutability.htm
),
the body returned by `macroexpand-all` should likely be copied using
`copy-tree`.

In GNU Emacs 30.0.50 (build 6, x86_64-pc-linux-gnu, GTK+ Version
 3.24.36, cairo version 1.17.6) of 2023-01-05 built on vibhavp-mbp
Repository revision: 15fc7b3cde92e420f48dfe188251e6af4d832af5
Repository branch: master
System Description: Arch Linux

Configured using:
 'configure --with-pgtk --with-sqlite3 --with-native-compilation=yes
 --with-all --without-compress-install --enable-link-time-optimization
 -C 'CFLAGS=-march=native -mtune=native -O3 -g3 -ggdb3 -gdwarf-5''

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY
PDUMPER PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM GTK3 ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
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  electric-indent-mode: t
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  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: (only . t)
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media puny dired
dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068
epg-config gnus-util text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader cl-
loaddefs
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help-mode bytecomp byte-compile cl-lib sendmail rfc2047 rfc2045
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elisp-mode mwheel term/pgtk-win pgtk-win term/common-win pgtk-dnd
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cyrillic chinese composite emoji-zwj charscript charprop case-table
epa-hook jka-cmpr-hook help abbrev obarray oclosure cl-preloaded button
loaddefs theme-loaddefs faces cus-face macroexp files window
text-properties overlay sha1 md5 base64 format env code-pages mule
custom widget keymap hashtable-print-readable backquote threads
dbusbind
inotify dynamic-setting system-font-setting font-render-setting cairo
gtk pgtk lcms2 multi-tty make-network-process native-compile emacs)

Memory information:
((conses 16 78180 10230)
 (symbols 48 7127 0)
 (strings 32 19480 1383)
 (string-bytes 1 595292)
 (vectors 16 16343)
 (vector-slots 8 326128 14214)
 (floats 8 28 51)
 (intervals 56 237 0)
 (buffers 984 11))