Further work on suppressing shell history in Tramp

Fixes: debbugs:19731

* net/tramp-sh.el (tramp-histfile-override): Fix docstring.
(tramp-open-shell, tramp-maybe-open-connection): Set also
HISTFILESIZE and HISTSIZE when needed.

lisp/ChangeLog

+2015-02-03  Michael Albinus  <michael.albinus@gmx.de>
+
+	* net/tramp-sh.el (tramp-histfile-override): Fix docstring.
+	(tramp-open-shell, tramp-maybe-open-connection): Set also
+	HISTFILESIZE and HISTSIZE when needed.  (Bug#19731)
+
 2015-02-02  Artur Malabarba  <bruce.connor.am@gmail.com>
 
 	* emacs-lisp/package.el (package--find-non-dependencies): New

lisp/net/tramp-sh.el

@@ -71,10 +71,11 @@ When setting to a string, it redirects the shell history to that
 file.  Be careful when setting to \"/dev/null\"; this might
 result in undesired results when using \"bash\" as shell.
 
-The value t, the default value, unsets any setting of HISTFILE.
-If you set this variable to nil, however, the *override* is
-disabled, so the history will go to the default storage
-location, e.g. \"$HOME/.sh_history\"."
+The value t, the default value, unsets any setting of HISTFILE,
+and sets both HISTFILESIZE and HISTSIZE to 0.  If you set this
+variable to nil, however, the *override* is disabled, so the
+history will go to the default storage location,
+e.g. \"$HOME/.sh_history\"."
   :group 'tramp
   :version "25.1"
   :type '(choice (const :tag "Do not override HISTFILE" nil)
@@ -3901,15 +3902,16 @@ file exists and nonzero exit status otherwise."
       ;; when called as sh) on startup; this way, we avoid the startup
       ;; file clobbering $PS1.  $PROMPT_COMMAND is another way to set
       ;; the prompt in /bin/bash, it must be discarded as well.
+      ;; $HISTFILE is set according to `tramp-histfile-override'.
       (tramp-send-command
        vec (format
 	    "exec env ENV='' %s PROMPT_COMMAND='' PS1=%s PS2='' PS3='' %s %s"
-            (if tramp-histfile-override
-                (concat
-		 "HISTFILE="
-		 (if (stringp tramp-histfile-override)
-		     (tramp-shell-quote-argument tramp-histfile-override) ""))
-              "")
+	    (if (stringp tramp-histfile-override)
+		(format "HISTFILE=%s"
+			(tramp-shell-quote-argument tramp-histfile-override))
+	      (if tramp-histfile-override
+		  "HISTFILE='' HISTFILESIZE=0 HISTSIZE=0"
+		""))
 	    (tramp-shell-quote-argument tramp-end-of-output)
 	    shell (or extra-args ""))
        t))
@@ -4631,10 +4633,13 @@ connection if a previous connection has died for some reason."
 		(delete-process p))
 	      (setenv "TERM" tramp-terminal-type)
 	      (setenv "LC_ALL" "en_US.utf8")
-	      (when tramp-histfile-override
-                (setenv "HISTFILE"
-			(and (stringp tramp-histfile-override)
-			     tramp-histfile-override)))
+	      (if (stringp tramp-histfile-override)
+		  (setenv "HISTFILE" tramp-histfile-override)
+		(if tramp-histfile-override
+		    (progn
+		      (setenv "HISTFILE")
+		      (setenv "HISTFILESIZE" "0")
+		      (setenv "HISTSIZE" "0"))))
 	      (setenv "PROMPT_COMMAND")
 	      (setenv "PS1" tramp-initial-end-of-output)
 	      (let* ((target-alist (tramp-compute-multi-hops vec))