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

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Daniel Mendler <mail <at> daniel-mendler.de>, Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: psainty <at> orcon.net.nz, 78719 <at> debbugs.gnu.org, 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: Sun, 08 Jun 2025 15:35:03 +0300

> From: Daniel Mendler <mail <at> daniel-mendler.de>
> Cc: bug-gnu-emacs <at> gnu.org,  Eli Zaretskii <eliz <at> gnu.org>,  Drew Adams
>  <drew.adams <at> oracle.com>,  juri <at> linkov.net
> Date: Sun, 08 Jun 2025 14:21:52 +0200
> 
> Phil Sainty <psainty <at> orcon.net.nz> writes:
> 
> > 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.
> 
> What is the purpose of having a separate function
> `string-try-completion'? I think it is confusing if the function
> respects the `completion-regexp-list' and `completion-ignore-case'
> dynamic variables, and if we end up with three functions
> `try-completion', `string-try-completion', and
> `completions-try-completion'.
> 
> Why not only provide a single function `string-expand-prefix' with
> additional keyword or optional arguments:
> 
> (cl-defun string-common-prefix (strings &key ignore-case regexps predicate))
> 
> The STRING or initial prefix argument seems redundant, since one can
> always use the empty string, and use `string-prefix-p' to check a
> desired prefix, or am I missing something?
> 
> (cl-defun string-common-prefix (strings &key prefix ignore-case regexps predicate))

Adding Stefan to the discussion.

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