bug#38796: 26.3; `view-lossage': Use a variable for the lossage limit

[Tino Calancha <tino.calancha@gmail.com>]

Eli Zaretskii <eliz@gnu.org> writes:

>> FWIW I have been running Emacs almost 3 months using this branch
>> with no issues.
>> If Eli is OK with it, I can merge it to master next week.
>
> Sorry, OK with what? where's the patch which I should agree with?

Branch origin/bug#38796-lossage-limit

The following is the difference with master branch when I updated
the branch (last August 27th):
--8<-----------------------------cut here---------------start------------->8---
diff --git a/doc/emacs/help.texi b/doc/emacs/help.texi
index 06ad5a583d..34a354891b 100644
--- a/doc/emacs/help.texi
+++ b/doc/emacs/help.texi
@@ -573,10 +573,13 @@ Misc Help
 
 @kindex C-h l
 @findex view-lossage
+@findex lossage-size
   If something surprising happens, and you are not sure what you typed,
 use @kbd{C-h l} (@code{view-lossage}).  @kbd{C-h l} displays your last
-300 input keystrokes and the commands they invoked.  If you see
-commands that you are not familiar with, you can use @kbd{C-h k} or
+input keystrokes and the commands they invoked.  By default, Emacs
+stores the last 300 events; if you wish, you can change this number with
+the command @code{lossage-size}.
+If you see commands that you are not familiar with, you can use @kbd{C-h k} or
 @kbd{C-h f} to find out what they do.
 
 @kindex C-h e
diff --git a/etc/NEWS b/etc/NEWS
index 964b626d7b..8bb3527d85 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -85,6 +85,10 @@ useful on systems such as FreeBSD which ships only with "etc/termcap".
 \f
 * Changes in Emacs 28.1
 
++++
+** The new command 'lossage-limit' controls the maximum number
+of keystrokes and commands recorded.
+
 +++
 ** New variables that hold default buffer names for shell output.
 The new constants 'shell-command-buffer-name' and
@@ -92,6 +96,9 @@ The new constants 'shell-command-buffer-name' and
 for the output of, respectively, synchronous and async shell
 commands.
 
+** The new command lossage-size' allow users to set the maximum
+number of keystrokes and commands recorded.
+
 ** Support for '(box . SIZE)' 'cursor-type'.
 By default, 'box' cursor always has a filled box shape.  But if you
 specify 'cursor-type' to be '(box . SIZE)', the cursor becomes a hollow
diff --git a/lisp/comint.el b/lisp/comint.el
index be0e32b9e0..afc8395b36 100644
--- a/lisp/comint.el
+++ b/lisp/comint.el
@@ -2393,7 +2393,7 @@ comint-send-invisible
 Then send it to the process running in the current buffer.
 The string is sent using `comint-input-sender'.
 Security bug: your string can still be temporarily recovered with
-\\[view-lossage]; `clear-this-command-keys' can fix that."
+\\[view-lossage]; `clear-this-command-keys' and `lossage-size' can fix that."
   (interactive "P")			; Defeat snooping via C-x ESC ESC
   (let ((proc (get-buffer-process (current-buffer)))
 	(prefix
diff --git a/lisp/edmacro.el b/lisp/edmacro.el
index 71474c0289..52cbf5b5a6 100644
--- a/lisp/edmacro.el
+++ b/lisp/edmacro.el
@@ -35,8 +35,8 @@
 ;;  * `M-x' followed by a command name, to edit a named command
 ;;    whose definition is a keyboard macro.
 ;;
-;;  * `C-h l' (view-lossage), to edit the 300 most recent keystrokes
-;;    and install them as the "current" macro.
+;;  * `C-h l' (view-lossage), to edit the 300 most recent
+;;    keystrokes and install them as the "current" macro.
 ;;
 ;;  * any key sequence whose definition is a keyboard macro.
 ;;
diff --git a/lisp/help.el b/lisp/help.el
index 1b0149616f..d3b0e02f08 100644
--- a/lisp/help.el
+++ b/lisp/help.el
@@ -455,9 +455,10 @@ view-external-packages
   (info "(efaq)Packages that do not come with Emacs"))
 
 (defun view-lossage ()
-  "Display last few input keystrokes and the commands run.
+  "Display last input keystrokes and the commands run.
 For convenience this uses the same format as
 `edit-last-kbd-macro'.
+See `lossage-size' to update the number of recorded keystrokes.
 
 To record all your input, use `open-dribble-file'."
   (interactive)
diff --git a/lisp/term.el b/lisp/term.el
index e77c2c1331..e39d03e8cd 100644
--- a/lisp/term.el
+++ b/lisp/term.el
@@ -2236,7 +2236,8 @@ term-read-noecho
 
 Note that the keystrokes comprising the text can still be recovered
 \(temporarily) with \\[view-lossage].  This may be a security bug for some
-applications."
+applications.  See `clear-this-command-keys' and `lossage-size' for ways
+to fix that."
   (declare (obsolete read-passwd "27.1"))
   (let ((ans "")
 	(c 0)
diff --git a/src/keyboard.c b/src/keyboard.c
index 5fa58abce1..bf8d75b602 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -103,15 +103,16 @@ Copyright (C) 1985-1989, 1993-1997, 1999-2020 Free Software Foundation,
 /* True in the single-kboard state, false in the any-kboard state.  */
 static bool single_kboard;
 
-#define NUM_RECENT_KEYS (300)
-
 /* Index for storing next element into recent_keys.  */
 static int recent_keys_index;
 
 /* Total number of elements stored into recent_keys.  */
 static int total_keys;
 
-/* This vector holds the last NUM_RECENT_KEYS keystrokes.  */
+/* Size of the recent_keys vector */
+static int lossage_limit = 300;
+
+/* This vector holds the last lossage_limit keystrokes.  */
 static Lisp_Object recent_keys;
 
 /* Vector holding the key sequence that invoked the current command.
@@ -294,6 +295,7 @@ #define GROW_RAW_KEYBUF							\
 /* Pointer to next place to store character in kbd_buffer.  */
 static union buffered_input_event *kbd_store_ptr;
 
+
 /* The above pair of variables forms a "queue empty" flag.  When we
    enqueue a non-hook event, we increment kbd_store_ptr.  When we
    dequeue a non-hook event, we increment kbd_fetch_ptr.  We say that
@@ -1421,10 +1423,10 @@ command_loop_1 (void)
       /* Execute the command.  */
 
       {
-	total_keys += total_keys < NUM_RECENT_KEYS;
+	total_keys += total_keys < lossage_limit;
 	ASET (recent_keys, recent_keys_index,
 	      Fcons (Qnil, cmd));
-	if (++recent_keys_index >= NUM_RECENT_KEYS)
+	if (++recent_keys_index >= lossage_limit)
 	  recent_keys_index = 0;
       }
       Vthis_command = cmd;
@@ -3248,15 +3250,15 @@ record_char (Lisp_Object c)
       int ix1, ix2, ix3;
 
       if ((ix1 = recent_keys_index - 1) < 0)
-	ix1 = NUM_RECENT_KEYS - 1;
+	ix1 = lossage_limit - 1;
       ev1 = AREF (recent_keys, ix1);
 
       if ((ix2 = ix1 - 1) < 0)
-	ix2 = NUM_RECENT_KEYS - 1;
+	ix2 = lossage_limit - 1;
       ev2 = AREF (recent_keys, ix2);
 
       if ((ix3 = ix2 - 1) < 0)
-	ix3 = NUM_RECENT_KEYS - 1;
+	ix3 = lossage_limit - 1;
       ev3 = AREF (recent_keys, ix3);
 
       if (EQ (XCAR (c), Qhelp_echo))
@@ -3307,12 +3309,12 @@ record_char (Lisp_Object c)
     {
       if (!recorded)
 	{
-	  total_keys += total_keys < NUM_RECENT_KEYS;
+	  total_keys += total_keys < lossage_limit;
 	  ASET (recent_keys, recent_keys_index,
                 /* Copy the event, in case it gets modified by side-effect
                    by some remapping function (bug#30955).  */
                 CONSP (c) ? Fcopy_sequence (c) : c);
-	  if (++recent_keys_index >= NUM_RECENT_KEYS)
+	  if (++recent_keys_index >= lossage_limit)
 	    recent_keys_index = 0;
 	}
       else if (recorded < 0)
@@ -3326,10 +3328,10 @@ record_char (Lisp_Object c)
 
 	  while (recorded++ < 0 && total_keys > 0)
 	    {
-	      if (total_keys < NUM_RECENT_KEYS)
+	      if (total_keys < lossage_limit)
 		total_keys--;
 	      if (--recent_keys_index < 0)
-		recent_keys_index = NUM_RECENT_KEYS - 1;
+		recent_keys_index = lossage_limit - 1;
 	      ASET (recent_keys, recent_keys_index, Qnil);
 	    }
 	}
@@ -10410,6 +10412,62 @@ DEFUN ("input-pending-p", Finput_pending_p, Sinput_pending_p, 0, 1, 0,
 	  ? Qt : Qnil);
 }
 
+/* Reallocate recent_keys copying the keystrokes in the right order */
+static void
+update_recent_keys (int new_size, int kept_keys)
+{
+  int osize = ASIZE (recent_keys);
+  eassert (recent_keys_index < osize);
+  eassert (kept_keys <= min (osize, new_size));
+  Lisp_Object v = make_nil_vector (new_size);
+  int i, idx;
+  for (i = 0; i < kept_keys; ++i)
+    {
+      idx = recent_keys_index - kept_keys + i;
+      while (idx < 0)
+        idx += osize;
+      ASET (v, i, AREF (recent_keys, idx));
+    }
+  recent_keys = v;
+  total_keys = kept_keys;
+  recent_keys_index = total_keys % new_size;
+  lossage_limit = new_size;
+
+}
+
+DEFUN ("lossage-size", Flossage_size, Slossage_size, 0, 1,
+       "(list (read-number \"new-size: \" (lossage-size)))",
+       doc: /* Return the maximum number of saved keystrokes.
+Called with ARG, then set this number to ARG.
+
+The saved keystrokes are the records shown by `view-lossage'.
+If you want to disable the lossage records, then set this maximum to a
+small number, e.g. 0.
+usage: (lossage-size &optional ARG) */)
+  (Lisp_Object arg)
+{
+  if (NILP(arg))
+    return make_fixnum(lossage_limit == 1 ? 0 : lossage_limit);
+
+  if (!FIXNATP (arg))
+    user_error ("Value must be a non-negative integer");
+  int osize = ASIZE (recent_keys);
+  eassert (lossage_limit == osize);
+  int new_size = XFIXNAT (arg);
+
+  if (new_size == osize)
+    return Qnil;
+  /* Internally, the minimum lossage_limit is 1; users will likely use
+     0 to disable the lossage, thus here we change 0 -> 1.  */
+  if (new_size == 0)
+    new_size = 1;
+
+  int kept_keys = new_size > osize ? total_keys : min (new_size, total_keys);
+  update_recent_keys (new_size, kept_keys);
+
+  return Qnil;
+}
+
 DEFUN ("recent-keys", Frecent_keys, Srecent_keys, 0, 1, 0,
        doc: /* Return vector of last few events, not counting those from keyboard macros.
 If INCLUDE-CMDS is non-nil, include the commands that were run,
@@ -10419,21 +10477,21 @@ DEFUN ("recent-keys", Frecent_keys, Srecent_keys, 0, 1, 0,
   bool cmds = !NILP (include_cmds);
 
   if (!total_keys
-      || (cmds && total_keys < NUM_RECENT_KEYS))
+      || (cmds && total_keys < lossage_limit))
     return Fvector (total_keys,
 		    XVECTOR (recent_keys)->contents);
   else
     {
       Lisp_Object es = Qnil;
-      int i = (total_keys < NUM_RECENT_KEYS
+      int i = (total_keys < lossage_limit
 	       ? 0 : recent_keys_index);
-      eassert (recent_keys_index < NUM_RECENT_KEYS);
+      eassert (recent_keys_index < lossage_limit);
       do
 	{
 	  Lisp_Object e = AREF (recent_keys, i);
 	  if (cmds || !CONSP (e) || !NILP (XCAR (e)))
 	    es = Fcons (e, es);
-	  if (++i >= NUM_RECENT_KEYS)
+	  if (++i >= lossage_limit)
 	    i = 0;
 	} while (i != recent_keys_index);
       es = Fnreverse (es);
@@ -10531,7 +10589,7 @@ DEFUN ("this-single-command-raw-keys", Fthis_single_command_raw_keys,
 DEFUN ("clear-this-command-keys", Fclear_this_command_keys,
        Sclear_this_command_keys, 0, 1, 0,
        doc: /* Clear out the vector that `this-command-keys' returns.
-Also clear the record of the last 300 input events, unless optional arg
+Also clear the record of the last input events, unless optional arg
 KEEP-RECORD is non-nil.  */)
   (Lisp_Object keep_record)
 {
@@ -11686,7 +11744,7 @@ syms_of_keyboard (void)
     staticpro (&modifier_symbols);
   }
 
-  recent_keys = make_nil_vector (NUM_RECENT_KEYS);
+  recent_keys = make_nil_vector (lossage_limit);
   staticpro (&recent_keys);
 
   this_command_keys = make_nil_vector (40);
@@ -11736,6 +11794,7 @@ syms_of_keyboard (void)
   defsubr (&Srecursive_edit);
   defsubr (&Sinternal_track_mouse);
   defsubr (&Sinput_pending_p);
+  defsubr (&Slossage_size);
   defsubr (&Srecent_keys);
   defsubr (&Sthis_command_keys);
   defsubr (&Sthis_command_keys_vector);
diff --git a/test/src/keyboard-tests.el b/test/src/keyboard-tests.el
index 1988ba51a7..d4ac4a518d 100644
--- a/test/src/keyboard-tests.el
+++ b/test/src/keyboard-tests.el
@@ -32,5 +32,23 @@ keyboard-unread-command-events
                         (read-event nil nil 2))
                  ?\C-b)))
 
+(ert-deftest keyboard-lossage-size ()
+  "Test `lossage-size'."
+  (dolist (val (list 100 300 400 400 500 1000 700 300))
+    (lossage-size val)
+    (should (= val (lossage-size))))
+  (let ((current-size (lossage-size)))
+    ;; Set lossage size to 1 and 0 are equivalent
+    (lossage-size 0)
+    (should (zerop (lossage-size)))
+    (lossage-size 1)
+    (should (zerop (lossage-size)))
+    (lossage-size current-size)
+    ;; Argument must be a natural number
+    (should-error (lossage-size -5))
+    (should-error (lossage-size "200"))
+    (should (= (lossage-size) current-size))))
+
+
 (provide 'keyboard-tests)
 ;;; keyboard-tests.el ends here

--8<-----------------------------cut here---------------end--------------->8---