menu: add GRUB_RIGHT_TO_SELECT to toggle select-by-right-arrow-key

Normally, GRUB allows using a combination of the Return/Enter (`\n' and
`\r'), Ctrl-F, and the right arrow key to select a menu item. However, on
some keyboards (especially those half-height arrow keys found on laptop
computers), it is very easy to accidentally select a menu item when the
user meant to press the up/down arrow key.

Implement an GRUB_RIGHT_TO_SELECT option (boolean) to enable/disable right
arrow key for selecting menu items.

Co-developed-by: Mag Mell <[email protected]>
Signed-off-by: Mingcong Bai <[email protected]>

Author: MingcongBai

docs/grub.texi

@@ -1593,6 +1593,10 @@ This option may be set to a list of GRUB module names separated by spaces.
 Each module will be loaded as early as possible, at the start of
 @file{grub.cfg}.
 
+@item GRUB_RIGHT_TO_SELECT
+This option may be set to specify whether the right arrow key may be used
+to make a selection. This option defaults to @samp{true}.
+
 @end table
 
 The following options are still accepted for compatibility with existing

grub-core/normal/menu.c

@@ -32,6 +32,7 @@
 #include <grub/script_sh.h>
 #include <grub/gfxterm.h>
 #include <grub/dl.h>
+#include <grub/env.h>
 
 /* Time to delay after displaying an error message about a default/fallback
    entry failing to boot.  */
@@ -579,11 +580,16 @@ run_menu (grub_menu_t menu, int nested, int *auto_boot, int *notify_boot)
   int default_entry, current_entry;
   int timeout;
   enum timeout_style timeout_style;
+  bool right_to_select;
 
   *notify_boot = 1;
 
   default_entry = get_entry_number (menu, "default");
 
+  /* Read if the right arrow key is enabled for selection. Default to `true'
+     if unset. */
+  right_to_select = grub_env_get_bool ("right_to_select", true);
+
   /* If DEFAULT_ENTRY is not within the menu entries, fall back to
      the first entry.  */
   if (default_entry < 0 || default_entry >= menu->size)
@@ -762,9 +768,17 @@ run_menu (grub_menu_t menu, int nested, int *auto_boot, int *notify_boot)
 	    case '\r':
 	    case GRUB_TERM_KEY_RIGHT:
 	    case GRUB_TERM_CTRL | 'f':
-	      menu_fini ();
-              *auto_boot = 0;
-	      return current_entry;
+	      /* Right arrow key to select only when boolean value
+		 `right_to_select' is set to `true' or not specified
+		 (defaults to `true'). */
+	      if ((c != GRUB_TERM_KEY_RIGHT) ||
+		  right_to_select)
+		{
+		  menu_fini ();
+		  *auto_boot = 0;
+		  return current_entry;
+		}
+	      break;
 
 	    case GRUB_TERM_ESC:
 	      if (nested)

util/grub-mkconfig.in

@@ -254,7 +254,8 @@ export GRUB_DEFAULT \
   GRUB_ENABLE_CRYPTODISK \
   GRUB_BADRAM \
   GRUB_OS_PROBER_SKIP_LIST \
-  GRUB_DISABLE_SUBMENU
+  GRUB_DISABLE_SUBMENU \
+  GRUB_RIGHT_TO_SELECT
 
 if test "x${grub_cfg}" != "x"; then
   rm -f "${grub_cfg}.new"

util/grub.d/00_header.in

@@ -37,6 +37,7 @@ if [ "x${GRUB_DEFAULT}" = "x" ] ; then GRUB_DEFAULT=0 ; fi
 if [ "x${GRUB_DEFAULT}" = "xsaved" ] ; then GRUB_DEFAULT='${saved_entry}' ; fi
 if [ "x${GRUB_TIMEOUT}" = "x" ] ; then GRUB_TIMEOUT=5 ; fi
 if [ "x${GRUB_GFXMODE}" = "x" ] ; then GRUB_GFXMODE=auto ; fi
+if [ "x${GRUB_RIGHT_TO_SELECT}" = "x" ] ; then GRUB_RIGHT_TO_SELECT=true ; fi
 
 if [ "x${GRUB_DEFAULT_BUTTON}" = "x" ] ; then GRUB_DEFAULT_BUTTON="$GRUB_DEFAULT" ; fi
 if [ "x${GRUB_DEFAULT_BUTTON}" = "xsaved" ] ; then GRUB_DEFAULT_BUTTON='${saved_entry}' ; fi
@@ -373,3 +374,8 @@ fi
 if [ "x${GRUB_BADRAM}" != "x" ] ; then
   echo "badram ${GRUB_BADRAM}"
 fi
+
+# Whether to allow selecting with the right arrow key.
+cat << EOF
+set right_to_select=${GRUB_RIGHT_TO_SELECT}
+EOF