bug#72414: 29.4; use-package :defer keyword does not honor ":defer nil"

[Derek Upham via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

- The relevant file is "lisp/use-package/use-package-core.el".
- The function is "use-package-normalize-keywords".
- This is as of commit 4c6e9f5b004, current for this file on the
  "emacs-30" tag.

Near the bottom of the use-package-normalize-keywords function, we have
the following code block.

    ;; If at this point no :load, :defer or :no-require has been seen, then
    ;; :load the package itself.
    (when (and (not (plist-member args :load))
               (not (plist-member args :defer))
               (not (plist-member args :no-require)))
      (setq args (append args `(:load (,name)))))

The intent is that we add an immediate-load instruction to the keyword
list, if there is no reason to not add it.  We have a couple of possible
reasons to not add it:

1. There's already a :load keyword.
2. We have asked use-package to :defer loading.
3. We have asked use-package to not require the package, to avoid
   certain byte-compilation problems.

The Use-Package documentation section 3.2 goes into more detail about
the :defer keyword behavior in (2).

   If you customize the user option ‘use-package-always-defer’ to
   non-‘nil’, the ‘use-package’ macro will behave as if ‘:defer t’ is
   always specified.  This can be overridden for individual declarations
   using either ‘:defer nil’ or ‘:demand t’ (*note Forcing loading::).

The way the code above uses plist-member doesn't match the
documentation.  The test looks for the simple presence of a :defer
key/value, and doesn't distinguish between any of the possible values:
t, nil, or an integer.

Replacing plist-member with plist-get should fix the problem.  A ":defer
nil" would produce the same nil value as a missing :defer.




In GNU Emacs 29.4 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.42,
 cairo version 1.18.0) of 2024-06-29, modified by Debian built on sbuild
Windowing system distributor 'The X.Org Foundation', version 11.0.12101011
System Description: Debian GNU/Linux trixie/sid

Configured using:
 'configure --build x86_64-linux-gnu --prefix=/usr
 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
 --mandir=/usr/share/man --with-libsystemd --with-pop=yes
 --enable-locallisppath=/etc/emacs:/usr/local/share/emacs/29.4/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/29.4/site-lisp:/usr/share/emacs/site-lisp
 --with-sound=alsa --without-gconf --with-mailutils
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 --sharedstatedir=/var/lib --libexecdir=/usr/libexec
 --localstatedir=/var/lib --infodir=/usr/share/info
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 --with-sound=alsa --without-gconf --with-mailutils
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 -fstack-clash-protection -Wformat -Werror=format-security
 -fcf-protection -Wall' 'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2'
 LDFLAGS=-Wl,-z,relro'

Configured features:
ACL CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
JSON LCMS2 LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES
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THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XDBE XIM XINPUT2
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Important settings:
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix

-- 
Derek Upham
derek_upham@mailfence.com