From d83ee0224c3d239d2713103c13c71a9e048f239a Mon Sep 17 00:00:00 2001
From: Naoya Yamashita <conao3@gmail.com>
Date: Wed, 9 Sep 2020 09:52:39 +0900
Subject: [PATCH] Add gv-define-expander for plist-get

It is necessary to make plist-get as a generalized variable, and this
definition allows user to use setf and other useful functions on
plist-get.

* lisp/emacs-lisp/gv.el: Add gv-define-expander for plist-get

* lisp/emacs-lisp/gv-tests.el: Add new tests for plist-get
---
 lisp/emacs-lisp/gv.el            | 11 +++++++++
 test/lisp/emacs-lisp/gv-tests.el | 40 ++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/lisp/emacs-lisp/gv.el b/lisp/emacs-lisp/gv.el
index 78d86b9fc3..568bcf244b 100644
--- a/lisp/emacs-lisp/gv.el
+++ b/lisp/emacs-lisp/gv.el
@@ -417,6 +417,17 @@ alist-get
                                               `(delq ,p ,getter))))))
                             ,v))))))))))
 
+(gv-define-expander plist-get
+  (lambda (do plist prop)
+    (macroexp-let2 macroexp-copyable-p key prop
+      (gv-letplace (getter setter) plist
+        (macroexp-let2 nil p `(cdr (plist-member ,getter ',key))
+          (funcall do
+                   `(cadr ,p)
+                   (lambda (val)
+                     `(if ,p
+                          (setcar ,p ,val)
+                        ,(funcall setter `(cons ',key (cons ,val ,getter)))))))))))
 
 ;;; Some occasionally handy extensions.
 
diff --git a/test/lisp/emacs-lisp/gv-tests.el b/test/lisp/emacs-lisp/gv-tests.el
index 7a8402be07..10e3b531f3 100644
--- a/test/lisp/emacs-lisp/gv-tests.el
+++ b/test/lisp/emacs-lisp/gv-tests.el
@@ -156,6 +156,46 @@ gv-setter-edebug
       (eval-buffer)))
   (should (equal (get 'gv-setter-edebug 'gv-setter-edebug-prop) '(123))))
 
+(ert-deftest gv-plist-get ()
+  (require 'cl-lib)
+
+  ;; Simple setf usage for plist-get.
+  (should (equal (let ((target '(:a "a" :b "b" :c "c")))
+                   (setf (plist-get target :b) "modify")
+                   target)
+                 '(:a "a" :b "modify" :c "c")))
+
+  ;; Other function (cl-rotatef) usage for plist-get.
+  (should (equal (let ((target '(:a "a" :b "b" :c "c")))
+                   (cl-rotatef (plist-get target :b) (plist-get target :c))
+                   target)
+                 '(:a "a" :b "c" :c "b")))
+
+  ;; Add new key value pair at top of list if setf for missing key.
+  (should (equal (let ((target '(:a "a" :b "b" :c "c")))
+                   (setf (plist-get target :d) "modify")
+                   target)
+                 '(:d "modify" :a "a" :b "b" :c "c")))
+
+  ;; Rotate with missing value.
+  ;; The value corresponding to the missing key is assumed to be nil.
+  (should (equal (let ((target '(:a "a" :b "b" :c "c")))
+                   (cl-rotatef (plist-get target :b) (plist-get target :d))
+                   target)
+                 '(:d "b" :a "a" :b nil :c "c")))
+
+  ;; Simple setf usage for plist-get. (symbol plist)
+  (should (equal (let ((target '(a "a" b "b" c "c")))
+                   (setf (plist-get target 'b) "modify")
+                   target)
+                 '(a "a" b "modify" c "c")))
+
+  ;; Other function (cl-rotatef) usage for plist-get. (symbol plist)
+  (should (equal (let ((target '(a "a" b "b" c "c")))
+                   (cl-rotatef (plist-get target 'b) (plist-get target 'c))
+                   target)
+                 '(a "a" b "c" c "b"))))
+
 ;; `ert-deftest' messes up macroexpansion when the test file itself is
 ;; compiled (see Bug #24402).
 
-- 
2.28.0