Give Lisp control on the lossage size

Add a command 'lossage-size' to set the maximum
number or recorded keystrokes (Bug#38796).

* src/keyboard.c (lossage_limit):
Static variable with the current lossage size limit.
(MIN_NUM_RECENT_KEYS): Renamed from NUM_RECENT_KEYS.
Set it as 100 and use it as the minimum value for lossage_limit.
Keep the same default for the vector size as before (300).
(lossage-size): New command.
(update_recent_keys): Helper function.
(command_loop_1)
(record_char)
(recent-keys)
(syms_of_keyboard): Use lossage_limit as the vector size.

* lisp/help.el (view-lossage): Mention the new command in the docstring.
* etc/NEWS (Changes in Emacs 28.1): Announce this change.
* doc/emacs/help.texi (Misc Help): Update manual.
* test/src/keyboard-tests.el (keyboard-lossage-size): Add test.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/src/keyboard-tests.el b/test/src/keyboard-tests.el
index 1988ba51a76..970a53555f9 100644
--- a/test/src/keyboard-tests.el
+++ b/test/src/keyboard-tests.el
@@ -32,5 +32,20 @@
                         (read-event nil nil 2))
                  ?\C-b)))
 
+(ert-deftest keyboard-lossage-size ()
+  "Test `lossage-size'."
+  (let ((min-value 100)
+        (lossage-orig (lossage-size)))
+    (dolist (factor (list 1 3 4 5 10 7 3))
+      (let ((new-lossage (* factor min-value)))
+        (should (= new-lossage (lossage-size new-lossage)))))
+    ;; Wrong type
+    (should-error (lossage-size -5))
+    (should-error (lossage-size "200"))
+    ;; Less that minimum value
+    (should-error (lossage-size (1- min-value)))
+    (should (= lossage-orig (lossage-size lossage-orig)))))
+
+
 (provide 'keyboard-tests)
 ;;; keyboard-tests.el ends here