Mention 'C-h' in echo for unfinished commands

* etc/NEWS: Mention it here.

* lisp/cus-start.el (standard): Add type and version for it.

* src/keyboard.c (echo-keystrokes-help): New user option
(https://lists.gnu.org/archive/html/emacs-devel/2024-02/msg00174.html).

* src/keyboard.c (echo_dash): Use it.

1 files changed, 13 insertions, 0 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index 1f7253a7da1..6d3db5ab615 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -589,6 +589,15 @@ echo_dash (void)
   AUTO_STRING (dash, "-");
   kset_echo_string (current_kboard,
                     concat2 (KVAR (current_kboard, echo_string), dash));
+
+  if (echo_keystrokes_help)
+    {
+      AUTO_STRING (help, " (\\`C-h' for help)");
+      kset_echo_string (current_kboard,
+                        concat2 (KVAR (current_kboard, echo_string),
+                                 calln (Qsubstitute_command_keys, help)));
+    }
+
   echo_now ();
 }
 
@@ -13228,6 +13237,10 @@ The value may be integer or floating point.
 If the value is zero, don't echo at all.  */);
   Vecho_keystrokes = make_fixnum (1);
 
+  DEFVAR_BOOL ("echo-keystrokes-help", echo_keystrokes_help,
+               doc: /* Non-nil means append small help text to the unfinished commands' echo. */);
+  echo_keystrokes_help = true;
+
   DEFVAR_LISP ("polling-period", Vpolling_period,
               doc: /* Interval between polling for input during Lisp execution.
 The reason for polling is to make C-g work to stop a running program.