Apply connecion-local variables for shells

* doc/misc/tramp.texi (Remote processes): Show use of connection-local
variables.  Don't mention Emacs 23 anymore.
(Frequently Asked Questions): Precise Emacs and MS Windows version.

* lisp/files-x.el (connection-local-normalize-criteria):
Suppress nil properties.
(connection-local-set-profiles, with-connection-local-profiles):
Adapt docstring.

* lisp/shell.el (shell): Apply connecion-local variables.

doc/misc/tramp.texi

@@ -2499,6 +2499,42 @@ Starting with Emacs 24, when @option{explicit-shell-file-name} is
 equal to @code{nil}, calling @code{shell} interactively will prompt
 for a shell name.
 
+Starting with Emacs 26, you could use connection-local variables for
+setting different values of @option{explicit-shell-file-name} for
+different remote hosts.
+@ifinfo
+@pxref{Connection Local Variables, , , elisp}
+@end ifinfo
+
+@lisp
+@group
+(connection-local-set-profile-variables
+  'remote-bash
+  '((explicit-shell-file-name . "/bin/bash")
+    (explicit-bash-args . ("-i"))))
+@end group
+
+@group
+(connection-local-set-profile-variables
+  'remote-ksh
+  '((explicit-shell-file-name . "/bin/ksh")
+    (explicit-ksh-args . ("-i"))))
+@end group
+
+@group
+(connection-local-set-profiles
+  '(:application 'tramp :protocol "ssh" :machine "localhost")
+  'remote-bash)
+@end group
+
+@group
+(connection-local-set-profiles
+  `(:application 'tramp :protocol "sudo"
+    :user "root" :machine ,(system-name))
+  'remote-ksh)
+@end group
+@end lisp
+
 
 @subsection Running @code{shell-command} on a remote host
 @cindex shell-command
@@ -2542,11 +2578,10 @@ uid=0(root) gid=0(root) groups=0(root)
 @end group
 @end example
 
-@code{eshell} in Emacs 23.2 added custom @code{su} and @code{sudo}
-commands that set the default directory correctly for the
-@file{*eshell*} buffer.  @value{tramp} silently updates
-@option{tramp-default-proxies-alist} with an entry for this directory
-(@pxref{Multi-hops}):
+@code{eshell} added custom @code{su} and @code{sudo} commands that set
+the default directory correctly for the @file{*eshell*} buffer.
+@value{tramp} silently updates @option{tramp-default-proxies-alist}
+with an entry for this directory (@pxref{Multi-hops}):
 
 @example
 @group
@@ -2763,11 +2798,12 @@ Where is the latest @value{tramp}?
 @item
 Which systems does it work on?
 
-The package works successfully on Emacs 23, Emacs 24, and Emacs 25.
+The package works successfully on Emacs 23, Emacs 24, Emacs 25, and
+Emacs 26.
 
 While Unix and Unix-like systems are the primary remote targets,
 @value{tramp} has equal success connecting to other platforms, such as
-MS Windows XP/Vista/7.
+MS Windows 7/8/10.
 
 
 @item

lisp/files-x.el

@@ -585,7 +585,7 @@ Return a new ordered plist list containing only property names from PROPERTIES."
    nil
    (mapcar
     (lambda (property)
-      (when (plist-member criteria property)
+      (when (and (plist-member criteria property) (plist-get criteria property))
         (list property (plist-get criteria property))))
     properties)))
 
@@ -606,12 +606,10 @@ using this connection, see `connection-local-criteria-alist'."
 
 ;;;###autoload
 (defun connection-local-set-profiles (criteria &rest profiles)
-  "Add PROFILES for remote servers.
-CRITERIA is either a regular expression identifying a remote
-server, or a function with one argument IDENTIFICATION, which
-returns non-nil when a remote server shall apply PROFILE's
-variables.  If CRITERIA is nil, it always applies.
-PROFILES are the names of a connection profile (a symbol).
+  "Add PROFILES for CRITERIA.
+CRITERIA is a plist identifying a connection and the application
+using this connection, see `connection-local-criteria-alist'.
+PROFILES are the names of connection profiles (a symbol).
 
 When a connection to a remote server is opened and CRITERIA
 matches to that server, the connection-local variables from
@@ -678,7 +676,7 @@ will not be changed."
 ;;;###autoload
 (defmacro with-connection-local-profiles (profiles &rest body)
   "Apply connection-local variables according to PROFILES in current buffer.
-Execute BODY, and unwind connection local variables."
+Execute BODY, and unwind connection-local variables."
   (declare (indent 1) (debug t))
   `(let ((enable-connection-local-variables t)
          (old-buffer-local-variables (buffer-local-variables))

lisp/shell.el

@@ -711,36 +711,43 @@ Otherwise, one argument `-i' is passed to the shell.
                  ;; If the current buffer is a dead shell buffer, use it.
                  (current-buffer)))
 
-  ;; On remote hosts, the local `shell-file-name' might be useless.
-  (if (and (called-interactively-p 'any)
-	   (file-remote-p default-directory)
-	   (null explicit-shell-file-name)
-	   (null (getenv "ESHELL")))
-      (with-current-buffer buffer
-	(set (make-local-variable 'explicit-shell-file-name)
-             (expand-file-name
-              (file-local-name
-	       (read-file-name
-		"Remote shell path: " default-directory shell-file-name
-		t shell-file-name))))))
+  (with-current-buffer buffer
+    (when (file-remote-p default-directory)
+      ;; Apply connection-local variables.
+      (hack-connection-local-variables-apply
+       `(:application 'tramp
+         :protocol ,(file-remote-p default-directory 'method)
+         :user ,(file-remote-p default-directory 'user)
+         :machine ,(file-remote-p default-directory 'host)))
 
-  ;; The buffer's window must be correctly set when we call comint (so
-  ;; that comint sets the COLUMNS env var properly).
-  (pop-to-buffer buffer)
-  (unless (comint-check-proc buffer)
-    (let* ((prog (or explicit-shell-file-name
-		     (getenv "ESHELL") shell-file-name))
-	   (name (file-name-nondirectory prog))
-	   (startfile (concat "~/.emacs_" name))
-	   (xargs-name (intern-soft (concat "explicit-" name "-args"))))
-      (unless (file-exists-p startfile)
-	(setq startfile (concat user-emacs-directory "init_" name ".sh")))
-      (apply 'make-comint-in-buffer "shell" buffer prog
-	     (if (file-exists-p startfile) startfile)
-	     (if (and xargs-name (boundp xargs-name))
-		 (symbol-value xargs-name)
-	       '("-i")))
-      (shell-mode)))
+      ;; On remote hosts, the local `shell-file-name' might be useless.
+      (if (and (called-interactively-p 'any)
+               (null explicit-shell-file-name)
+               (null (getenv "ESHELL")))
+          (set (make-local-variable 'explicit-shell-file-name)
+               (expand-file-name
+                (file-local-name
+                 (read-file-name
+                  "Remote shell path: " default-directory shell-file-name
+                  t shell-file-name))))))
+
+    ;; The buffer's window must be correctly set when we call comint
+    ;; (so that comint sets the COLUMNS env var properly).
+    (pop-to-buffer buffer)
+    (unless (comint-check-proc buffer)
+      (let* ((prog (or explicit-shell-file-name
+                       (getenv "ESHELL") shell-file-name))
+             (name (file-name-nondirectory prog))
+             (startfile (concat "~/.emacs_" name))
+             (xargs-name (intern-soft (concat "explicit-" name "-args"))))
+        (unless (file-exists-p startfile)
+          (setq startfile (concat user-emacs-directory "init_" name ".sh")))
+        (apply 'make-comint-in-buffer "shell" buffer prog
+               (if (file-exists-p startfile) startfile)
+               (if (and xargs-name (boundp xargs-name))
+                   (symbol-value xargs-name)
+                 '("-i")))
+        (shell-mode))))
   buffer)
 
 ;;; Directory tracking