Fix 'this-command-keys' wrt prefix argument

* src/keyboard.c (command_loop_1): Restore the feature whereby C-u
was part of this-command-keys, but not of this-single-command-keys.
(Bug#22107)

* lisp/simple.el (internal-echo-keystrokes-prefix): Add
commentary about the function's return value.

1 files changed, 3 insertions, 1 deletions

diff --git a/lisp/simple.el b/lisp/simple.el
index 17b9c918ead..9e0388efe45 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -3818,7 +3818,9 @@ see other processes running on the system, use `list-system-processes'."
 (setq prefix-command--last-echo nil)
 
 (defun internal-echo-keystrokes-prefix ()
-  ;; BEWARE: Called directly from the C code.
+  ;; BEWARE: Called directly from C code.
+  ;; If the return value is non-nil, it means we are in the middle of
+  ;; a command with prefix, such as a command invoked with prefix-arg.
   (if (not prefix-command--needs-update)
       prefix-command--last-echo
     (setq prefix-command--last-echo