bug#41436: 26.1; How to list upgradable packages only

[Eduardo Mercovich]

Dear Emacs Devs.

Along with my thanks, I'd like to report a feature request, as per the
discussion in the Emacs Reddit group
(https://www.reddit.com/r/emacs/comments/gnci5o/how_to_list_upgradable_packages_only/)
and the suggestion from https://www.reddit.com/user/cpitclaudel/

Here is the case: 

--8<---------------cut here---------------start------------->8---

Upon refreshing the repos, the emacs package manager (PM) tells us
if/how many packages we have to upgrade. With U we can mark them all,
and with X let the PM do it's job (uninstall old versions, install the
new ones). Up to here, everything is great. 

However, being a rookie, I' afraid of upgrading 28 packages at once
since some things may break, so I prefer to upgrade them in small groups
in a more controlled way. 

But, for my life, even after quite some searching and reading I can't
find how to filter the list by that status (the command
package-menu-filter does something different or I don't understand how
to use it for this), so I can see only the packages that can be
upgraded. With that list in front of me, I can pick which ones to
upgrade, slowly and in a more controlled path. 

I'm sure something like that exists, but obviously I'm not finding the
right keywords.

--8<---------------cut here---------------end--------------->8---

Again, thanks a lot for sharing your work with all of us. :)

What follows is part of my local install, although it's probably useless
in this case.

In GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
of 2019-09-23, modified by Debian built on x86-grnet-01
Windowing system distributor 'The X.Org Foundation', version 11.0.12004000
System Description:     Debian GNU/Linux 10 (buster)

Configured using:
'configure --build x86_64-linux-gnu --prefix=/usr
--sharedstatedir=/var/lib --libexecdir=/usr/lib
--localstatedir=/var/lib --infodir=/usr/share/info
--mandir=/usr/share/man --enable-libsystemd --with-pop=yes
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
--with-sound=alsa --without-gconf --with-mailutils --build
x86_64-linux-gnu --prefix=/usr --sharedstatedir=/var/lib
--libexecdir=/usr/lib --localstatedir=/var/lib
--infodir=/usr/share/info --mandir=/usr/share/man --enable-libsystemd
--with-pop=yes
--enable-locallisppath=/etc/emacs:/usr/local/share/emacs/26.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/26.1/site-lisp:/usr/share/emacs/site-lisp
--with-sound=alsa --without-gconf --with-mailutils --with-x=yes
--with-x-toolkit=gtk3 --with-toolkit-scroll-bars 'CFLAGS=-g -O2
-fdebug-prefix-map=/build/emacs-StqULU/emacs-26.1+1=.
-fstack-protector-strong -Wformat -Werror=format-security -Wall'
'CPPFLAGS=-Wdate-time -D_FORTIFY_SOURCE=2' LDFLAGS=-Wl,-z,relro'
Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS NOTIFY
ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 THREADS LIBSYSTEMD LCMS2
Important settings:
 value of $LANG: es_AR.UTF-8
 locale-coding-system: utf-8-unix

Major mode: Org

Minor modes in effect:
 diff-auto-refine-mode: t
 shell-dirtrack-mode: t
 auto-image-file-mode: t
 flyspell-mode: t
 org-indent-mode: t
 org-roam-mode: t
 display-time-mode: t
 desktop-save-mode: t
 pdf-occur-global-minor-mode: t
 wrap-region-mode: t
 async-bytecomp-package-mode: t
 helm-mode: t
 global-hi-lock-mode: t
 hi-lock-mode: t
 electric-pair-mode: t
 delete-selection-mode: t
 savehist-mode: t
 smartparens-global-mode: t
 smartparens-mode: t
 org-bullets-mode: t
 beacon-mode: t
 override-global-mode: t
 tooltip-mode: t
 global-eldoc-mode: t
 electric-indent-mode: t
 mouse-wheel-mode: t
 file-name-shadow-mode: t
 global-font-lock-mode: t
 font-lock-mode: t
 auto-composition-mode: t
 auto-encryption-mode: t
 auto-compression-mode: t
 line-number-mode: t
 global-visual-line-mode: t
 visual-line-mode: t
 transient-mark-mode: t
 abbrev-mode: t

Memory information:
((conses 16 2194798 1708575)
(symbols 48 68434 188)
(miscs 40 1962 3428)
(strings 32 296075 153673)
(string-bytes 1 9977187)
(vectors 16 84246)
(vector-slots 8 2071025 227004)
(floats 8 1245 490)
(intervals 56 271031 239055)
(buffers 992 38))

--
eduardo mercovich

Donde se cruzan tus talentos 
con las necesidades del mundo, 
ahí está tu vocación. 
(Anónimo)