Subject: 30.0.50; minibuffer-visible-completions=t makes RET in completion-in-region a no-op with nothing selected

From: Spencer Baugh <[email-masked]>
Date: Mon, 29 Jan 2024 13:49:53 -0500

1. emacs -Q
2. In scratch:
(current- M-<tab>
3. Observe *Completions* pops up.
4. RET
5. *Completions* goes away and a newline is inserted.

Compare:

1. emacs -Q --eval '(setq minibuffer-visible-completions t)'
2. In scratch:
(current- M-<tab>
3. Observe *Completions* pops up.
4. RET
5. *Completions* goes away but no newline is inserted, and "No match" is
   printed.

I think the behavior with minibuffer-visible-completions=t is
unintuitive.  And it just duplicates what you can achieve with C-g
(closes *Completions*), so it's not very useful.

Even if I do:
(current- M-<tab> buf RET

which is sufficient to uniquely identify current-buffer, RET does not
complete to current-buffer, instead it just says "No match".

With minibuffer-visible-completions=t, I suggest RET with no completion
selected in completion-in-region should exit completion and insert a
newline.

Or maybe, slightly more radically, RET with no completion selected in
completion-in-region should select the first matching completion given
the current completion region?  At least one user expected that
behavior.

Another alternative is that RET doesn't close *Completions* at all,
which would match minibuffer behavior better.  I'm not a huge fan of
that, but it's more useful than the current behavior of RET.

Since there are a few alternatives, perhaps we could have a defcustom
for the RET behavior in completion-in-region.  I think the default
should be closing *Completions* and inserting a newline, since that
matches minibuffer-visible-completions=nil.

If this sounds reasonable I can write a patch implementing these.

In GNU Emacs 30.0.50 (build 24, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.15.12, Xaw scroll bars) of 2024-01-29 built on
 igm-qws-u22796a Repository revision:
 cbc8bdc1386a4bc9c420d8ab06b844c6f6928c35 Repository branch: master
 Windowing system distributor 'The X.Org Foundation', version
 11.0.12011000 System Description: Rocky Linux 8.9 (Green Obsidian)

Configured using:
 'configure -C 'CFLAGS=-O0 -g3' --with-gif=ifavailable
 --with-x-toolkit=lucid'

Configured features:
CAIRO DBUS FREETYPE GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NOTIFY INOTIFY PDUMPER PNG RSVG
SECCOMP SOUND SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS X11 XDBE XIM
XINPUT2 XPM LUCID ZLIB

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

Major mode: Lisp Interaction

Minor modes in effect:
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  global-font-lock-mode: t
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  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:
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Memory information:
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