bug#49924: 28.0.50; `package-quickstart-refresh' fails for "long" (according to `print-length') `package-alist'

[Pal Gloss <pcfeb0009@gmx.com>]

Following #49922, I was able to diagnose & fix an issue with
`package-quickstart-refresh' when `print-length' is lower than
`(length package-activated-list)'.  There are two possible
user-visible symptoms, caused by the presence of the "..." ellipsis
in the `package-quickstart-file':
1. A warning in *Compile-Log* about a free variable ‘\.\.\.’
2. When restarting emacs, an error message about a missing package
   named "..."

I did not make any experiments, but I am pretty sure that it also would
be possible to produce a broken `package-quickstart-file' with
`print-level' suitably low (1 or 2, maybe even 3?).




;; !!! This reproduction scenario ruins your                       !!!
;; !!! $HOME/.emacs.d/package-quickstart.el unless you are careful !!!
;; !!! Run it with:                                                !!!
;; env HOME=/tmp emacs -Q

(let ((print-length 2))
  (require 'package)
  (package-quickstart-refresh))

;; There is a warning in *Compile-Log*
;;
;; Compiling file c:/msys64/tmp/.emacs.d/package-quickstart.el at Sat Aug  7 10:09:10 2021
;; Entering directory ‘c:/msys64/tmp/.emacs.d/’
;; package-quickstart.el:4:30: Warning: reference to free variable ‘\.\.\.’

Now look inside the generated "package-quickstart.el" with

(find-file package-quickstart-file)

And you will see "(setq package-activated-list ...)" (literally with 3
dots) instead of "(setq package-activated-list (append <text elided for brevity>))".



There is another way to reproduce it that can work with a more "likely"
(or reasonable) value of `print-length', but this is not with `emacs -Q'
because it requires a non-NIL `package-alist', i.e. an existing emacs
configuration with some outside packages:

;; !!! This reproduction scenario ruins your                 !!!
;; !!! `package-quickstart-file'.  Regenerate it afterwards. !!!
;; Assuming you have at least 4 external packages activated in
;; your configuration
(progn
  (package-initialize)
  (let ((print-length (- (length package-alist) 1)))
    (package-quickstart-refresh)))

Now look inside the generated "package-quickstart.el" with

(find-file package-quickstart-file)

And you will see that a package named "..." is added to the
`package-activated-list'.  Next time you start emacs, the package
initialization will fail because there is no such package.





My work-around is to rebind `print-level' and `print-length' before
calling `package-quickstart-refresh' (I do so periodically in the
background):

;; -------- From my early-init.el file --------
;; Enable package quickstart ...
(funcall (or (get 'package-quickstart 'custom-set)
             'set-default)
         'package-quickstart t)
;; ... and make sure it stays up to date
(run-with-idle-timer
 120 ; seconds
 'repeat
 (lambda ()
   (let (;; don't abbreviate lists: the `package-activated-list' is long and
         ;; needs to be complete, otherwise Emacs will search for a package
         ;; called "...".
         (print-length nil)
         ;; I haven't had a problem with it yet, but better safe than sorry.
         (print-level nil))
     (package-quickstart-refresh))))
;; -------- End of my early-init.el file --------




In GNU Emacs 28.0.50 (build 1, x86_64-w64-mingw32)
 of 2021-08-06 built on <hostname>
Repository revision: 0afab352e02d7070a8ced2af53c1d01217400cdf
Repository branch: master
Windowing system distributor 'Microsoft Corp.', version 6.3.9600
System Description: Microsoft Windows 8.1 (v6.3.0.9600.20069)

Configured using:
 'configure --with-xml2 --with-zlib --without-pop
 --prefix=/home/username/emacs-native-comp/dest
 --without-compress-install --without-dbus --with-native-compilation
 --with-modules 'CFLAGS=-O2 -g3'
 PKG_CONFIG_PATH=/mingw64/lib/pkgconfig:/mingw64/share/pkgconfig'

Configured features:
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NOTIFY W32NOTIFY PDUMPER PNG RSVG SOUND THREADS TIFF TOOLKIT_SCROLL_BARS
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Important settings:
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  value of $LANG: en_US.UTF-8
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Major mode: ELisp/l

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Memory information:
((conses 16 174962 29708)
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