have <del> run #terrain

Having recently noticed that using <del> aka <delete> aka <rubout>
could work as a command, assign it to #terrain.  #terrain was the
only command in the "game" subset of commands as shown by '? i'
that didn't have any key assignment.

Since <delete> might be swapped with <backspace> on some terminals
and is a keypad key on the typical PC keyboard, it might not work
reliably depending on nethack's number_pad mode or the hardware
Num-Lock setting.  Players in either of those situations haven't
lost anything; they can still use extended command #terrain.

dat/cmdhelp

@@ -1,4 +1,4 @@
-&# cmdhelp
+&# cmdhelp - became obsolete when 'BINDINGS=key:command' got added
 &	Tell what command a keystroke invokes
 ^	Show the type of an adjacent trap
 ^[	Cancel command (same as ESCape key)
@@ -145,6 +145,7 @@ _	Travel via a shortest-path algorithm to a point on the map
 *	Show all equipment in use (combination of the ),[,=,",( commands)
 $	Count your gold
 +	List known spells
+Del	Display map without monsters or objects obstructing the view.
 #	Perform an extended command (use '#?' to list choices)
 &# number_pad:
 &#  -1 = numpad off, swap y with z (including Y with Z, ^Y with ^Z, M-y &c)

doc/Guidebook.mn

@@ -1,4 +1,4 @@
-.\" $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.405 $ $NHDT-Date: 1607693152 2020/12/11 13:25:52 $
+.\" $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.407 $ $NHDT-Date: 1607936398 2020/12/14 08:59:58 $
 .\"
 .\" This is an excerpt from the 'roff' man page from the 'groff' package.
 .\" Guidebook.mn currently does *not* fully adhere to these guidelines.
@@ -35,7 +35,7 @@
 .ds vr "NetHack 3.7
 .ds f0 "\*(vr
 .ds f1
-.ds f2 "December 11, 2020
+.ds f2 "December 13, 2020
 .
 .\" A note on some special characters:
 .\" \(lq = left double quote
@@ -1060,6 +1060,20 @@ Show discovered types for one class of objects.
 .lp !
 Escape to a shell.
 See \(lq#shell\(rq below for more details.
+.lp Del
+Show map without obstructions.
+You can view the explored portion of the current level's map without
+monsters; without monsters and objects; or without monsters, objects,
+and traps.
+.lp ""
+The <del> key is also shown as <delete> on some keyboards or <rubout>
+on others.
+It is sometimes displayed as \(ha? even though that is not an actual
+control character.
+.lp ""
+Many terminals have an option to swap the <delete> and <backspace> keys,
+so typing the <del> key might not execute this command.
+If that happens, you can use the extended command \(lq#terrain\(rq instead.
 .lp #
 Perform an extended command.
 .lp ""
@@ -1447,8 +1461,17 @@ Default key is \(oqA\(cq.
 Teleport around the level.
 Default key is \(oq\(haT\(cq.
 .lp "#terrain "
-Show bare map without displaying monsters, objects, or traps.
+Show map without obstructions.
+In normal play you can view the explored portion of the current level's
+map without monsters; without monsters and objects; or without monsters,
+objects, and traps.
+.lp ""
+In explore mode, you can choose to view the full map rather than just
+its explored portion.
+In debug mode there are additional choices.
+.lp ""
 Autocompletes.
+Default key is \(oq<del>\(cq or \(oq<delete>\(cq (see \fIDel\fP above).
 .lp #therecmdmenu
 Show a menu of possible actions in a location next to you.
 .lp "#throw   "

doc/Guidebook.tex

@@ -45,7 +45,7 @@
 %.au
 \author{Original version - Eric S. Raymond\\
 (Edited and expanded for 3.7 by Mike Stephenson and others)}
-\date{December 11, 2020}
+\date{December 13, 2020}
 
 \maketitle
 
@@ -1162,6 +1162,21 @@ Show discovered types for one class of objects.
 Escape to a shell.
 See ``\#shell'' below for more details.
 %.lp
+\item[\tb{Del}]
+Show map without obstructions.
+You can view the explored portion of the current level's map without
+monsters; without monsters and objects; or without monsters, objects,
+and traps.\\
+%.lp ""
+The <del> key is also shown as <delete> on some keyboards or <rubout>
+on others.
+It is sometimes displayed as \^{}? even though that is not an actual
+control character.\\
+%.lp ""
+Many terminals have an option to swap the <delete> and <backspace> keys,
+so typing the <del> key might not execute this command.
+If that happens, you can use the extended command ``\#terrain'' instead.
+%.lp
 \item[\tb{\#}]
 Perform an extended command.\\
 %.lp ""
@@ -1537,8 +1552,17 @@ Remove all armor. Default key is `{\tt A}'.
 Teleport around the level. Default key is `{\tt \^{}T}'.
 %.lp
 \item[\tb{\#terrain}]
-Show bare map without displaying monsters, objects, or traps.
+Show map without obstructions.
+In normal play you can view the explored portion of the current level's
+map without monsters; without monsters and objects; or without monsters,
+objects, and traps.\\
+%.lp ""
+In explore mode, you can choose to view the full map rather than just
+its explored portion.
+In debug mode there are additional choices.\\
+%.lp ""
 Autocompletes.
+Default key is `<del>' or `<delete>' (see {\it Del\/} above).
 %.lp
 \item[\tb{\#therecmdmenu}]
 Show a menu of possible actions in a location next to you.

doc/fixes37.0

@@ -1,4 +1,4 @@
-NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.391 $ $NHDT-Date: 1607901923 2020/12/13 23:25:23 $
+NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.392 $ $NHDT-Date: 1607936398 2020/12/14 08:59:58 $
 
 General Fixes and Modified Features
 -----------------------------------
@@ -670,6 +670,7 @@ let tourists read conical hats
 when "?i" (show key bindings) displays commands and their keys, also show
 	commands without any key (so useable via '#', or possibly menu, only;
 	the majority are debugging commands)
+assign default key binding for <del> or <delete> to execute #terrain
 
 
 Platform- and/or Interface-Specific New Features

src/cmd.c

@@ -1,4 +1,4 @@
-/* NetHack 3.7	cmd.c	$NHDT-Date: 1607641581 2020/12/10 23:06:21 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.432 $ */
+/* NetHack 3.7	cmd.c	$NHDT-Date: 1607936399 2020/12/14 08:59:59 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.433 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Robert Patrick Rankin, 2013. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -1913,7 +1913,11 @@ struct ext_func_tab extcmdlist[] = {
     { 'T', "takeoff", "take off one piece of armor", dotakeoff },
     { 'A', "takeoffall", "remove all armor", doddoremarm },
     { C('t'), "teleport", "teleport around the level", dotelecmd, IFBURIED },
-    { '\0', "terrain", "show map without obstructions",
+    /* \177 == <del> aka <delete> aka <rubout>; some terminals have an
+       option to swap it with <backspace> so if there's a key labeled
+       <delete> it may or may not actually invoke the #terrain command */
+    { '\177', "terrain",
+            "view map without monsters or objects obstructing it",
             doterrain, IFBURIED | AUTOCOMPLETE },
     { '\0', "therecmdmenu",
             "menu of commands you can do from here to adjacent spot",