GNU bug report logs - #78719
30.1; [PATCH] Add functions `string-common-prefix' and `string-try-completion'

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From: Phil Sainty <psainty <at> orcon.net.nz>
To: 78719 <at> debbugs.gnu.org
Cc: Daniel Mendler <mail <at> daniel-mendler.de>, Eli Zaretskii <eliz <at> gnu.org>, Drew Adams <drew.adams <at> oracle.com>, juri <at> linkov.net
Subject: bug#78719: 30.1; [PATCH] Add functions `string-common-prefix' and `string-try-completion'
Date: Mon, 09 Jun 2025 00:03:46 +1200

This is a spin-off from bug#78658 -- and following on from
https://debbugs.gnu.org/cgi/bugreport.cgi?bug=78658#65 in particular --
to add friendlier alternatives to `try-completion' for efficiently
obtaining a common string prefix or completion from a collection of
strings outside of the context of minibuffer completion.

E.g. when you simply want to know the longest common prefix from a
list of strings without having to deal with any completion variables
or edge-case return values.

Unlike `try-completion' which may return nil or t, the new functions
always return a string, simplifying their usage and (on account of
the "string-*" naming) making the functionality more discoverable
for programmers working with strings.

The function `string-try-completion' provides the general case and
is just like `try-completion' except for always returning a string.

The function `string-common-prefix' is the simpler case wanted for
bug#78658, taking fewer arguments and binding the variables
`completion-regexp-list' and `completion-ignore-case'.

I've pushed a branch scratch/string-common-prefix with the following
commit for review:
https://cgit.git.savannah.gnu.org/cgit/emacs.git/commit/?h=scratch/string-common-prefix&id=accfe19887f3573dd55f5272f92899afa1e2f446

(Plus a fixup commit removing the unintended additional NEWS entry.)


-Phil



In GNU Emacs 30.1 (build 2, x86_64-pc-linux-gnu, X toolkit, cairo
 version 1.16.0, Xaw scroll bars) of 2025-02-25 built on phil-lp
Repository revision: 8ac894e2246f25d2a2a97d866b10e6e0b0fede5a
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 
11.0.12101004
System Description: Ubuntu 22.04.5 LTS

Configured using:
 'configure --prefix=/home/phil/emacs/30.x.nc/usr/local
 --with-native-compilation=aot --with-x-toolkit=lucid --without-sound
 '--program-transform-name=s/^ctags$/ctags_emacs/''

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG
LCMS2 LIBSELINUX LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY PDUMPER PNG
RSVG SECCOMP SQLITE3 THREADS TIFF TOOLKIT_SCROLL_BARS TREE_SITTER WEBP
X11 XDBE XIM XPM LUCID ZLIB

Important settings:
  value of $LC_MONETARY: en_NZ.UTF-8
  value of $LC_NUMERIC: en_NZ.UTF-8
  value of $LC_TIME: en_NZ.UTF-8
  value of $LANG: en_GB.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8

Major mode: Magit Rev

Minor modes in effect:
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Load-path shadows:
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/home/phil/.emacs.d/el-get/el-get/el-get
/home/phil/.emacs.d/el-get/avy/avy hides 
/home/phil/.emacs.d/elpa/avy-0.5.0/avy
/home/phil/.emacs.d/el-get/dash/dash hides 
/home/phil/.emacs.d/elpa/dash-2.19.1/dash
/home/phil/.emacs.d/el-get/iedit/iedit hides 
/home/phil/.emacs.d/elpa/iedit-0.9.9.9.9/iedit
/home/phil/.emacs.d/my-lisp/psysh hides 
/home/phil/.emacs.d/elpa/psysh-0.4.9/psysh
/home/phil/.emacs.d/elpa/transient-0.7.9/transient hides 
/home/phil/emacs/30.x.nc/usr/local/share/emacs/30.1/lisp/transient
/home/phil/.emacs.d/el-get/which-key/which-key hides 
/home/phil/emacs/30.x.nc/usr/local/share/emacs/30.1/lisp/which-key

Features:
(shadow sort ecomplete mail-extr emacsbug tramp trampver
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magit-stash magit-reflog magit-bisect magit-push magit-pull magit-fetch
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Memory information:
((conses 16 1246250 374539) (symbols 48 43403 2)
 (strings 32 196192 27442) (string-bytes 1 7837076) (vectors 16 94255)
 (vector-slots 8 1904715 340289) (floats 8 927 9358)
 (intervals 56 128211 16974) (buffers 992 50))

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