Subject: 27.0.50; completing-read-multiple chokes on list of default values

From: "Basil L. Contovounesios" <[email-masked]>
Date: Wed, 10 Jan 2018 21:37:51 +0000

>From dac3aeb9a53efa53851b588d599f990cba592e49 Mon Sep 17 00:00:00 2001
From: "Basil L. Contovounesios" <[email-masked]>
Date: Wed, 10 Jan 2018 20:21:25 +0000
Subject: [PATCH] Support list of default values in completing-read-multiple

* lisp/emacs-lisp/crm.el (completing-read-multiple):
Consider head of DEF argument when specified as a list,
as per completing-read-default.
---
 lisp/emacs-lisp/crm.el | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/lisp/emacs-lisp/crm.el b/lisp/emacs-lisp/crm.el
index 5aa856f467..1a67494d3c 100644
--- a/lisp/emacs-lisp/crm.el
+++ b/lisp/emacs-lisp/crm.el
@@ -263,7 +263,8 @@ completing-read-multiple
 	       (input (read-from-minibuffer
 		       prompt initial-input map
 		       nil hist def inherit-input-method)))
-	  (and def (string-equal input "") (setq input def))
+          (when (and def (string-equal input ""))
+            (setq input (if (consp def) (car def) def)))
           ;; Remove empty strings in the list of read strings.
 	  (split-string input crm-separator t)))
     (remove-hook 'choose-completion-string-functions
-- 
2.15.1

Steps to reproduce:

1) emacs -Q
2) Evaluate the following form:

   (let ((l '("a" "b")))
     (completing-read-multiple "" l nil nil nil nil l))

3) C-m

I expect this to result in the string "a", as is the case when
completing-read-multiple is replaced with completing-read in step 2,
given the following excerpt from the docstring of c-r-m:

  The arguments are the same as those of `completing-read'.

Instead, the following error is signalled:

Debugger entered--Lisp error: (wrong-type-argument stringp ("a" "b"))
  string-match("[ \011]*,[ \011]*" ("a" "b") 0)
  split-string(("a" "b") "[ \011]*,[ \011]*" t)
  completing-read-multiple("" ("a" "b") nil nil nil nil ("a" "b"))

I attach a fix which follows the implementation of
completing-read-default.

Thanks,

-- 
Basil

In GNU Emacs 27.0.50 (build 14, x86_64-pc-linux-gnu, X toolkit, Xaw3d scroll bars)
 of 2018-01-10 built on thunk
Repository revision: b877e9aa0225ad186b544f127702e16c61b08444
Windowing system distributor 'The X.Org Foundation', version 11.0.11905000
System Description: Debian GNU/Linux testing (buster)