Add 'ring-resize' function

* lisp/emacs-lisp/ring.el (ring-resize): New function.  (Bug#32849)
* doc/lispref/sequences.texi (Rings): Document new function 'ring-resize'.
* etc/NEWS: Document new function 'ring-resize'.
* test/lisp/emacs-lisp/ring-tests.el (ring-test-ring-resize): New tests.

1 files changed, 37 insertions, 0 deletions

diff --git a/test/lisp/emacs-lisp/ring-tests.el b/test/lisp/emacs-lisp/ring-tests.el
index 0b4e3d9a694..9fa36aa3d33 100644
--- a/test/lisp/emacs-lisp/ring-tests.el
+++ b/test/lisp/emacs-lisp/ring-tests.el
@@ -162,6 +162,43 @@
     (should (= (ring-size ring) 5))
     (should (equal (ring-elements ring) '(3 2 1)))))
 
+(ert-deftest ring-resize/grow ()
+  (let ((ring (make-ring 3)))
+    (ring-insert ring 1)
+    (ring-insert ring 2)
+    (ring-insert ring 3)
+    (ring-resize ring 5)
+    (should (= (ring-size ring) 5))
+    (should (equal (ring-elements ring) '(3 2 1)))))
+
+(ert-deftest ring-resize/grow-empty ()
+  (let ((ring (make-ring 3)))
+    (ring-resize ring 5)
+    (should (= (ring-size ring) 5))
+    (should (equal (ring-elements ring) '()))))
+
+(ert-deftest ring-resize/grow-wrapped-ring ()
+  (let ((ring (make-ring 3)))
+    (ring-insert ring 1)
+    (ring-insert ring 2)
+    (ring-insert ring 3)
+    (ring-insert ring 4)
+    (ring-insert ring 5)
+    (ring-resize ring 5)
+    (should (= (ring-size ring) 5))
+    (should (equal (ring-elements ring) '(5 4 3)))))
+
+(ert-deftest ring-resize/shrink ()
+  (let ((ring (make-ring 5)))
+    (ring-insert ring 1)
+    (ring-insert ring 2)
+    (ring-insert ring 3)
+    (ring-insert ring 4)
+    (ring-insert ring 5)
+    (ring-resize ring 3)
+    (should (= (ring-size ring) 3))
+    (should (equal (ring-elements ring) '(5 4 3)))))
+
 (ert-deftest ring-tests-insert ()
   (let ((ring (make-ring 2)))
     (ring-insert+extend ring :a)