bug#35546: 27.0.50; setf return value for new alist entries is wrong

[Michael Heerdegen]

Tassilo Horn <tsdh@gnu.org> writes:

> According to the last sentence, I'd assume that
>
>   (setq my-alist nil)
>   (setf (alist-get 'foo my-alist) "foo-value")
>
> would return "foo-value", but infact it returns ((foo . "foo-value")).
> As soon as there is an association for 'foo, it returns the new value,
> i.e., "foo-value".

I agree.  I think fixing should be quite straightforward:

From 2fc149e3afa411f5b64c743de362378568f97bd6 Mon Sep 17 00:00:00 2001
From: Michael Heerdegen <michael_heerdegen@web.de>
Date: Mon, 6 May 2019 14:58:24 +0200
Subject: [PATCH] Fix alist-get gv setter not returning VAL

This fixes Bug#35546.

* lisp/emacs-lisp/gv.el (alist-get): Make setter return the set value
to preserve 'setf' semantics.
---
 lisp/emacs-lisp/gv.el | 26 ++++++++++++++------------
 1 file changed, 14 insertions(+), 12 deletions(-)

diff --git a/lisp/emacs-lisp/gv.el b/lisp/emacs-lisp/gv.el
index 4ea3ce84fc..bdd1574820 100644
--- a/lisp/emacs-lisp/gv.el
+++ b/lisp/emacs-lisp/gv.el
@@ -392,18 +392,20 @@ setf
                                  ,(funcall setter
                                            `(cons (setq ,p (cons ,k ,v))
                                                   ,getter)))))
-                         (cond
-                          ((null remove) set-exp)
-                          ((or (eql v default)
-                               (and (eq (car-safe v) 'quote)
-                                    (eq (car-safe default) 'quote)
-                                    (eql (cadr v) (cadr default))))
-                           `(if ,p ,(funcall setter `(delq ,p ,getter))))
-                          (t
-                           `(cond
-                             ((not (eql ,default ,v)) ,set-exp)
-                             (,p ,(funcall setter
-                                           `(delq ,p ,getter)))))))))))))))
+                         `(progn
+                            ,(cond
+                             ((null remove) set-exp)
+                             ((or (eql v default)
+                                  (and (eq (car-safe v) 'quote)
+                                       (eq (car-safe default) 'quote)
+                                       (eql (cadr v) (cadr default))))
+                              `(if ,p ,(funcall setter `(delq ,p ,getter))))
+                             (t
+                              `(cond
+                                ((not (eql ,default ,v)) ,set-exp)
+                                (,p ,(funcall setter
+                                              `(delq ,p ,getter))))))
+                            ,v))))))))))


 ;;; Some occasionally handy extensions.
--
2.20.1


Michael.