Fix corner case in prefix-arg handling for mouse events (Bug#1586).

* src/keyboard.c (command_loop_1): If a down-mouse event is unbound,
leave any prefix arg for the up event.

1 files changed, 12 insertions, 1 deletions

diff --git a/src/keyboard.c b/src/keyboard.c
index 3441f1dfd12..16300e6154c 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -1539,7 +1539,18 @@ command_loop_1 (void)
           message_with_string ("%s is undefined", keys, 0);
           KVAR (current_kboard, defining_kbd_macro) = Qnil;
           update_mode_lines = 1;
-          KVAR (current_kboard, Vprefix_arg) = Qnil;
+          /* If this is a down-mouse event, don't reset prefix-arg;
+             pass it to the command run by the up event.  */
+          if (EVENT_HAS_PARAMETERS (last_command_event))
+            {
+              Lisp_Object breakdown
+                = parse_modifiers (EVENT_HEAD (last_command_event));
+              int modifiers = XINT (XCAR (XCDR (breakdown)));
+              if (!(modifiers & down_modifier))
+                KVAR (current_kboard, Vprefix_arg) = Qnil;
+            }
+          else
+            KVAR (current_kboard, Vprefix_arg) = Qnil;
         }
       else
         {