bug#66224: [PATCH] Add optional PREDICATE argument to read-directory-name

[Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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Stefan Kangas <stefankangas@gmail.com> writes:

> Joseph Turner <joseph@breatheoutbreathe.in> writes:
>
>> Joseph Turner <joseph@breatheoutbreathe.in> writes:
>>
>>> Michael Heerdegen <michael_heerdegen@web.de> writes:
>>>
>>>> Joseph Turner via "Bug reports for GNU Emacs, the Swiss army knife of
>>>> text editors" <bug-gnu-emacs@gnu.org> writes:
>>>>
>>>>> I'm not sure what you mean. In both of the following examples, PREDICATE
>>>>> is used to narrow the completion candidates to only empty directories:
>>>>>
>>>>> (read-directory-name "Prompt: " "~/" nil t nil #'directory-empty-p)
>>>>> (read-directory-name "Prompt: " "~/" nil nil nil #'directory-empty-p)
>>>>
>>>> In the second version also non-empty directories will be accepted.
>>>
>>> Yes, PREDICATE narrows the completion candidates but doesn't determine a
>>> valid return value.
>>
>> Ping!  I'm happy to keep discussing this patch if others are interested.
>
> Could you please send the latest version of your patch?

Here you go!


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From 894e44bce60cf30c9e8bc8c5323eaed91d135bbb Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Thu, 28 Sep 2023 20:27:47 -0700
Subject: [PATCH] Add optional PREDICATE argument to read-directory-name

* lisp/files.el (read-directory-name): Add optional PREDICATE arg.
* doc/lispref/minibuf.texi (Reading File Names): Document change.
* etc/NEWS: Note change.
---
 doc/lispref/minibuf.texi |  7 +++++--
 etc/NEWS                 |  5 +++++
 lisp/files.el            | 13 ++++++++++---
 3 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/doc/lispref/minibuf.texi b/doc/lispref/minibuf.texi
index 620c58ec6e9..bf4d6e13d3a 100644
--- a/doc/lispref/minibuf.texi
+++ b/doc/lispref/minibuf.texi
@@ -1709,7 +1709,7 @@ If this variable is non-@code{nil}, @code{read-file-name} ignores case
 when performing completion.
 @end defopt
 
-@defun read-directory-name prompt &optional directory default require-match initial
+@defun read-directory-name prompt &optional directory default require-match initial predicate
 This function is like @code{read-file-name} but allows only directory
 names as completion alternatives.
 
@@ -1719,7 +1719,10 @@ combining @var{directory} (or the current buffer's default directory
 if @var{directory} is @code{nil}) and @var{initial}.  If both
 @var{default} and @var{initial} are @code{nil}, this function uses
 @var{directory} as substitute default, or the current buffer's default
-directory if @var{directory} is @code{nil}.
+directory if @var{directory} is @code{nil}.  When optional sixth
+argument @code{predicate} is non-nil, the union of @code{predicate}
+and @code{file-directory-p} is passed as the @code{predicate} argument
+to @code{read-file-name}.
 @end defun
 
 @defopt insert-default-directory
diff --git a/etc/NEWS b/etc/NEWS
index 1b3532b5657..fb9f6a0b43f 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -3541,6 +3541,11 @@ This function is called to see whether what the user has typed is a
 match.  This is also available from functions that call
 'completing-read', like 'read-file-name'.
 
+** 'read-directory-name' now accepts an optional PREDICATE argument.
+When optional sixth argument PREDICATE is non-nil, the union of
+PREDICATE and 'file-directory-p' is passed as the PREDICATE argument
+to 'read-file-name'.
+
 ** 'posn-col-row' can now give position data based on windows.
 Previously, it reported data only based on the frame.
 
diff --git a/lisp/files.el b/lisp/files.el
index b72f141c0ee..68855cd1c6d 100644
--- a/lisp/files.el
+++ b/lisp/files.el
@@ -807,7 +807,7 @@ See Info node `(elisp)Standard File Names' for more details."
     (dos-convert-standard-filename filename))
    (t filename)))
 
-(defun read-directory-name (prompt &optional dir default-dirname mustmatch initial)
+(defun read-directory-name (prompt &optional dir default-dirname mustmatch initial predicate)
   "Read directory name, prompting with PROMPT and completing in directory DIR.
 Value is not expanded---you must call `expand-file-name' yourself.
 Default name to DEFAULT-DIRNAME if user exits with the same
@@ -821,14 +821,21 @@ Fourth arg MUSTMATCH non-nil means require existing directory's name.
  Non-nil and non-t means also require confirmation after completion.
 Fifth arg INITIAL specifies text to start with.
 DIR should be an absolute directory name.  It defaults to
-the value of `default-directory'."
+the value of `default-directory'.
+When sixth arg PREDICATE is non-nil, the union of PREDICATE and
+`file-directory-p' is passed as the PREDICATE argument to
+`read-file-name'. Otherwise, only `file-directory-p' is passed."
   (unless dir
     (setq dir default-directory))
   (read-file-name prompt dir (or default-dirname
 				 (if initial (expand-file-name initial dir)
 				   dir))
 		  mustmatch initial
-		  'file-directory-p))
+                  (if predicate
+                      (lambda (filename)
+                        (and (file-directory-p filename)
+                             (funcall predicate filename)))
+                    #'file-directory-p)))
 
 \f
 (defun pwd (&optional insert)
-- 
2.41.0