bug#43393: 28.0.50; `M-x load-library` completion regression

[Stefan Monnier]

Package: Emacs
Version: 28.0.50


I noticed two regressions in `M-x load-library`:

    emacs -Q
    M-x load-library RET
    o/or TAB
    C-a C-k
    /us/sh/ TAB

The first TAB used to expand `o/or` to `org/org`.
and the second TAB used to expand `/us/sh/` to `/usr/share/`.

Both regressions seem to come from the same commit:

    commit ed44217d3245ddc8f2cf75c9499d5bb37848cfd7
    Author: Lars Ingebrigtsen <larsi@gnus.org>
    Date:   Tue Aug 27 09:46:28 2019 +0200
    
        Fix completion in `read-library-name'
        
        * lisp/emacs-lisp/find-func.el (read-library-name): Only list
        .el/.el.gz files when completing (bug#36945).

I only noticed the `o/or` regression recently, but have been annoyed by
the other regression for a while now but just always figured it was
a problem on my end and postponed looking into it to later (I have
a fair bunch of half-broken local hacks in the completion code).


        Stefan



In GNU Emacs 28.0.50 (build 1, i686-pc-linux-gnu, GTK+ Version 3.24.22, cairo 
version 1.16.0)
 of 2020-09-07 built on alfajor
Repository revision: 25ae39e261de3062c714826ab8001fd45bc98e21
Repository branch: work
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description: Debian GNU/Linux bullseye/sid

Configured using:
 'configure -C --with-modules --with-cairo --with-tiff=ifavailable
 'CFLAGS=-Wall -g3 -Og -Wno-pointer-sign'
 PKG_CONFIG_PATH=/home/monnier/lib/pkgconfig'

Configured features:
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LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS JSON PDUMPER

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

Major mode: InactiveMinibuffer

Minor modes in effect:
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  line-number-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-mouse hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-mouse
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-noweb-mode hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-noweb-mode
/home/monnier/src/emacs/elpa/packages/ess/obsolete/mouseme hides 
/home/monnier/src/emacs/elpa/packages/ess/mouseme
/home/monnier/src/emacs/elpa/packages/ess/obsolete/msdos hides 
/home/monnier/src/emacs/elpa/packages/ess/msdos
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-rutils hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-rutils
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-eldoc hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-eldoc
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-noweb hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-noweb
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-r-args hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-r-args
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-noweb-font-lock-mode 
hides /home/monnier/src/emacs/elpa/packages/ess/ess-noweb-font-lock-mode
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-r-a hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-r-a
/home/monnier/src/emacs/elpa/packages/ess/obsolete/ess-swv hides 
/home/monnier/src/emacs/elpa/packages/ess/ess-swv
/home/monnier/src/emacs/elpa/packages/cpio-mode/cpio-mode hides 
/home/monnier/src/emacs/work/lisp/cpio-mode
/home/monnier/src/emacs/elpa/packages/hyperbole/set hides 
/home/monnier/src/emacs/work/lisp/emacs-lisp/set
/home/monnier/src/emacs/elpa/packages/seq/seq hides 
/home/monnier/src/emacs/work/lisp/emacs-lisp/seq
/home/monnier/src/emacs/elpa/packages/landmark/landmark hides 
/home/monnier/src/emacs/work/lisp/obsolete/landmark
/home/monnier/src/emacs/elpa/packages/crisp/crisp hides 
/home/monnier/src/emacs/work/lisp/obsolete/crisp

Features:
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Memory information:
((conses 8 805998 92560)
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 (vectors 8 117268)
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564 166))