bug#65092: 30.0.50; C-h f shows malformed description for vc-mode

bug#65092: 30.0.50; C-h f shows malformed description for vc-mode

[Eshel Yaron via Bug reports for GNU Emacs, the Swiss army knife of text editors]

I seems to have stumbled upon an issue with type inference on the master
branch that causes `describe-function` to display the following
malformed description for the function `vc-mode`:

    vc-mode is a native-compiled Lisp function in ‘vc-hooks.el’.

    (vc-mode &optional ARG)

    Inferred type: (function (&optional t) (member Version Control minor
    mode.  This minor mode is automatically activated whenever you visit a
    file under control of one of the revision control systems in
    `vc-handled-backends'.  VC commands are globally reachable under the
    prefix `\[vc-prefix-map]': \{vc-prefix-map}))

    Version Control minor mode.
    This minor mode is automatically activated whenever you...

To reproduce, do `C-h f vc-mode RET` in `emacs -Q`.

Basically, it looks like the inferred type somehow includes the
function's docstring verbatim:

--8<---------------cut here---------------start------------->8---
(comp-function-type-spec 'vc-mode)
=> ((function (&optional t) (member "Version Control minor mode.
This minor mode is automatically activated whenever you visit a file under
control of one of the revision control systems in `vc-handled-backends'.
VC commands are globally reachable under the prefix `\\[vc-prefix-map]':
\\{vc-prefix-map}")) . inferred)
--8<---------------cut here---------------end--------------->8---




In GNU Emacs 30.0.50 (build 3, x86_64-apple-darwin22.5.0, NS
 appkit-2299.60 Version 13.4 (Build 22F66)) of 2023-08-03 built on
 Dazzs-MBP
Repository revision: 7b30e11b2ac5cd360db7ee8b6aed07bd918b93a2
Repository branch: master
Windowing system distributor 'Apple', version 10.3.2299
System Description:  macOS 13.4

Configured using:
 'configure 'CFLAGS=-g0 -O3' --with-native-compilation --with-json
 --with-imagemagick --with-tree-sitter --enable-link-time-optimization'

Configured features:
ACL DBUS GIF GMP GNUTLS IMAGEMAGICK JPEG JSON LCMS2 LIBXML2 MODULES
NATIVE_COMP NOTIFY KQUEUE NS PDUMPER PNG SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP XIM ZLIB

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

Major mode: Help

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  isearch-fold-quotes-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  buffer-read-only: t
  line-number-mode: t
  indent-tabs-mode: t
  transient-mark-mode: 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 mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils time-date shortdoc vc-annotate vc-dir ewoc
vc vc-filewise vc-git diff-mode easy-mmode vc-dispatcher compile
text-property-search comint ansi-osc ansi-color ring comp comp-cstr
warnings icons subr-x rx cl-seq cl-macs gv cl-extra bytecomp
byte-compile thingatpt help-fns radix-tree help-mode cl-loaddefs cl-lib
rmc iso-transl tooltip cconv eldoc paren electric uniquify ediff-hook
vc-hooks lisp-float-type elisp-mode 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 lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch easymenu
timer select scroll-bar mouse jit-lock font-lock syntax font-core
term/tty-colors frame minibuffer nadvice seq simple cl-generic
indonesian philippine 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 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 kqueue cocoa ns
lcms2 multi-tty make-network-process native-compile emacs)

Memory information:
((conses 16 117625 14245) (symbols 48 8927 0) (strings 32 28340 1637)
 (string-bytes 1 843928) (vectors 16 20095)
 (vector-slots 8 394629 13087) (floats 8 92 641) (intervals 56 470 0)
 (buffers 984 13))

bug#65092: 30.0.50; C-h f shows malformed description for vc-mode

[Eli Zaretskii]

> Date: Sat, 05 Aug 2023 14:25:11 +0300
> From:  Eshel Yaron via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> 
> I seems to have stumbled upon an issue with type inference on the master
> branch that causes `describe-function` to display the following
> malformed description for the function `vc-mode`:
> 
>     vc-mode is a native-compiled Lisp function in ‘vc-hooks.el’.
> 
>     (vc-mode &optional ARG)
> 
>     Inferred type: (function (&optional t) (member Version Control minor
>     mode.  This minor mode is automatically activated whenever you visit a
>     file under control of one of the revision control systems in
>     `vc-handled-backends'.  VC commands are globally reachable under the
>     prefix `\[vc-prefix-map]': \{vc-prefix-map}))
> 
>     Version Control minor mode.
>     This minor mode is automatically activated whenever you...
> 
> To reproduce, do `C-h f vc-mode RET` in `emacs -Q`.
> 
> Basically, it looks like the inferred type somehow includes the
> function's docstring verbatim:
> 
> --8<---------------cut here---------------start------------->8---
> (comp-function-type-spec 'vc-mode)
> => ((function (&optional t) (member "Version Control minor mode.
> This minor mode is automatically activated whenever you visit a file under
> control of one of the revision control systems in `vc-handled-backends'.
> VC commands are globally reachable under the prefix `\\[vc-prefix-map]':
> \\{vc-prefix-map}")) . inferred)
> --8<---------------cut here---------------end--------------->8---

Probably because vc-mode is a "dummy function", whatever that means.
IOW, we are shooting ourselves in the foot, it seems like.

Adding Andrea.

bug#65092: 30.0.50; C-h f shows malformed description for vc-mode

[Stefan Monnier via Bug reports for GNU Emacs, the Swiss army knife of text editors]

> I seems to have stumbled upon an issue with type inference on the master
> branch that causes `describe-function` to display the following
> malformed description for the function `vc-mode`:
>
>     vc-mode is a native-compiled Lisp function in ‘vc-hooks.el’.
>
>     (vc-mode &optional ARG)
>
>     Inferred type: (function (&optional t) (member Version Control minor
>     mode.  This minor mode is automatically activated whenever you visit a
>     file under control of one of the revision control systems in
>     `vc-handled-backends'.  VC commands are globally reachable under the
>     prefix `\[vc-prefix-map]': \{vc-prefix-map}))
>
>     Version Control minor mode.
>     This minor mode is automatically activated whenever you...
>
> To reproduce, do `C-h f vc-mode RET` in `emacs -Q`.
>
> Basically, it looks like the inferred type somehow includes the
> function's docstring verbatim:
>
> --8<---------------cut here---------------start------------->8---
> (comp-function-type-spec 'vc-mode)
> => ((function (&optional t) (member "Version Control minor mode.
> This minor mode is automatically activated whenever you visit a file under
> control of one of the revision control systems in `vc-handled-backends'.
> VC commands are globally reachable under the prefix `\\[vc-prefix-map]':
> \\{vc-prefix-map}")) . inferred)
> --8<---------------cut here---------------end--------------->8---

This output is actually "correct" 🙁
I've just pushed a fix for it in `master` by giving an actual body to
the function, in addition to its doc string.


        Stefan