Tramp requires Emacs 24.4

* doc/misc/tramp.texi (Frequently Asked Questions):
Use `with-eval-after-load'. in example.

* doc/misc/trampver.texi: Set variable emacsver.

* lisp/net/tramp.el (tramp-send-string, tramp-call-process)
(tramp-call-process-region, tramp-process-lines):
* lisp/net/tramp-adb.el (tramp-adb-handle-file-truename)
(tramp-adb-sh-fix-ls-output, tramp-adb-maybe-open-connection):
* lisp/net/tramp-gvfs.el (tramp-gvfs-get-directory-attributes)
(tramp-gvfs-handle-file-notify-add-watch)
* lisp/net/tramp-sh.el (tramp-sh-handle-file-truename)
(tramp-do-copy-or-rename-file-out-of-band)
(tramp-sh-handle-file-notify-add-watch, tramp-find-executable)
(tramp-set-remote-path)
(tramp-open-connection-setup-interactive-shell)
(tramp-maybe-open-connection, tramp-send-command):
* lisp/net/tramp-smb.el (tramp-smb-handle-copy-directory)
(tramp-smb-handle-file-acl, tramp-smb-handle-process-file)
(tramp-smb-handle-set-file-acl)
(tramp-smb-handle-start-file-process)
(tramp-smb-maybe-open-connection):
* lisp/net/tramp-sudoedit.el (tramp-sudoedit-handle-set-file-acl):
(tramp-sudoedit-send-command): Use `string-join' and `string-empty-p'.

* lisp/net/tramp-adb.el:
* lisp/net/tramp-archive.el:
* lisp/net/tramp-integration.el:
* lisp/net/tramp-ftp.el: Use `with-eval-after-load'.

* lisp/net/tramp-cmds.el (tramp-cleanup-connection)
(tramp-cleanup-all-connections): Cancel timer.

* lisp/net/tramp-compat.el (subr-x): Require.
(default-toplevel-value): Don't make it a defalias.

* lisp/net/tramp-gvfs.el: Use `dbus-event-error-functions'.  Do
not special handle `split-string'.

* lisp/net/tramp.el: Require Emacs 24.4.
(tramp-password-prompt-regexp): Use `password-word-equivalents'.
(tramp-user-error): Use `user-error'.
(tramp-replace-environment-variables): Use `substitute-env-vars'.
(tramp-wait-for-regexp): Rearrange `with-current-buffer' call.
(tramp-get-local-gid): Use `group-gid'.

* lisp/net/trampver.el: Check for Emacs 24.4.

* test/lisp/net/tramp-tests.el (tramp-test02-file-name-dissect)
(tramp-test02-file-name-dissect-simplified)
(tramp-test02-file-name-dissect-separate)
(tramp-test03-file-name-host-rules)
(tramp-test03-file-name-method-rules): Don't check for `user-error'.

12 files changed, 144 insertions, 189 deletions

diff --git a/lisp/net/tramp-adb.el b/lisp/net/tramp-adb.el
index 008a5cedd8b..c8b9e7ae09c 100644
--- a/lisp/net/tramp-adb.el
+++ b/lisp/net/tramp-adb.el
@@ -257,17 +257,15 @@ pass to the OPERATION."
 	      (setq thisstep (pop steps))
 	      (tramp-message
 	       v 5 "Check %s"
-	       (mapconcat #'identity
-			  (append '("") (reverse result) (list thisstep))
-			  "/"))
+	       (string-join
+		(append '("") (reverse result) (list thisstep)) "/"))
 	      (setq symlink-target
 		    (tramp-compat-file-attribute-type
 		     (file-attributes
 		      (tramp-make-tramp-file-name
-		       v (mapconcat #'identity
-				    (append
-				     '("") (reverse result) (list thisstep))
-				    "/")))))
+		       v
+		       (string-join
+			(append '("") (reverse result) (list thisstep)) "/")))))
 	      (cond ((string= "." thisstep)
 		     (tramp-message v 5 "Ignoring step `.'"))
 		    ((string= ".." thisstep)
@@ -302,9 +300,9 @@ pass to the OPERATION."
 	    ;; Combine list to form string.
 	    (setq result
 		  (if result
-		      (mapconcat #'identity (cons "" result) "/")
+		      (string-join (cons "" result) "/")
 		    "/"))
-	    (when (and is-dir (or (string= "" result)
+	    (when (and is-dir (or (string-empty-p result)
 				  (not (string= (substring result -1) "/"))))
 	      (setq result (concat result "/"))))
 
@@ -479,7 +477,7 @@ Emacs dired can't find files."
 		 #'tramp-adb-ls-output-time-less-p
 	       #'tramp-adb-ls-output-name-less-p))))
       (delete-region (point-min) (point-max))
-      (insert "  " (mapconcat #'identity sorted-lines "\n  ")))
+      (insert "  " (string-join sorted-lines "\n  ")))
     ;; Add final newline.
     (goto-char (point-max))
     (unless (bolp) (insert "\n"))))
@@ -1232,7 +1230,7 @@ connection if a previous connection has died for some reason."
 		 (prompt (md5 (concat (prin1-to-string process-environment)
 				      (current-time-string)))))
 	    (tramp-message
-	     vec 6 "%s" (mapconcat #'identity (process-command p) " "))
+	     vec 6 "%s" (string-join (process-command p) " "))
 	    ;; Wait for initial prompt.  On some devices, it needs an
 	    ;; initial RET, in order to get it.
             (sleep-for 0.1)
@@ -1300,16 +1298,16 @@ connection if a previous connection has died for some reason."
 
 ;; `connection-local-set-profile-variables' and
 ;; `connection-local-set-profiles' exists since Emacs 26.1.
-(eval-after-load "shell"
-  '(progn
-     (tramp-compat-funcall
-      'connection-local-set-profile-variables
-      'tramp-adb-connection-local-default-profile
-      tramp-adb-connection-local-default-profile)
-     (tramp-compat-funcall
-      'connection-local-set-profiles
-      `(:application tramp :protocol ,tramp-adb-method)
-      'tramp-adb-connection-local-default-profile)))
+(with-eval-after-load 'shell
+  (progn
+    (tramp-compat-funcall
+     'connection-local-set-profile-variables
+     'tramp-adb-connection-local-default-profile
+     tramp-adb-connection-local-default-profile)
+    (tramp-compat-funcall
+     'connection-local-set-profiles
+     `(:application tramp :protocol ,tramp-adb-method)
+     'tramp-adb-connection-local-default-profile)))
 
 (add-hook 'tramp-unload-hook
 	  (lambda ()
diff --git a/lisp/net/tramp-archive.el b/lisp/net/tramp-archive.el
index 7e17fde7306..b329d4a1b11 100644
--- a/lisp/net/tramp-archive.el
+++ b/lisp/net/tramp-archive.el
@@ -372,14 +372,14 @@ pass to the OPERATION."
 ;; `tramp-archive-file-name-handler' must be placed before `url-file-handler'.
 (when url-handler-mode (tramp-register-file-name-handlers))
 
-(eval-after-load 'url-handler
-  '(progn
-     (add-hook 'url-handler-mode-hook #'tramp-register-file-name-handlers)
-     (add-hook
-      'tramp-archive-unload-hook
-      (lambda ()
-	(remove-hook
-	 'url-handler-mode-hook #'tramp-register-file-name-handlers)))))
+(with-eval-after-load 'url-handler
+  (progn
+    (add-hook 'url-handler-mode-hook #'tramp-register-file-name-handlers)
+    (add-hook
+     'tramp-archive-unload-hook
+     (lambda ()
+       (remove-hook
+	'url-handler-mode-hook #'tramp-register-file-name-handlers)))))
 
 
 ;; File name conversions.
diff --git a/lisp/net/tramp-cmds.el b/lisp/net/tramp-cmds.el
index f1e1d8271ff..007b98f94fe 100644
--- a/lisp/net/tramp-cmds.el
+++ b/lisp/net/tramp-cmds.el
@@ -116,6 +116,12 @@ When called interactively, a Tramp connection has to be selected."
       (delete-process (tramp-get-connection-process vec)))
     (tramp-flush-connection-properties vec)
 
+    ;; Cancel timer.
+    (dolist (timer timer-list)
+      (when (and (eq (timer--function timer) 'tramp-timeout-session)
+		 (tramp-file-name-equal-p vec (car (timer--args timer))))
+	(cancel-timer timer)))
+
     ;; Remove buffers.
     (dolist
 	(buf (list (get-buffer (tramp-buffer-name vec))
@@ -163,9 +169,12 @@ This includes password cache, file cache, connection cache, buffers."
 		(delete (car proxies) tramp-default-proxies-alist)
 		proxies tramp-default-proxies-alist)
 	(setq proxies (cdr proxies)))))
-    (when (and tramp-default-proxies-alist tramp-save-ad-hoc-proxies)
-      (customize-save-variable
-       'tramp-default-proxies-alist tramp-default-proxies-alist))
+  (when (and tramp-default-proxies-alist tramp-save-ad-hoc-proxies)
+    (customize-save-variable
+     'tramp-default-proxies-alist tramp-default-proxies-alist))
+
+  ;; Cancel timers.
+  (cancel-function-timers 'tramp-timeout-session)
 
   ;; Remove buffers.
   (dolist (name (tramp-list-tramp-buffers))
diff --git a/lisp/net/tramp-compat.el b/lisp/net/tramp-compat.el
index 15b737d281b..4f01f8d372f 100644
--- a/lisp/net/tramp-compat.el
+++ b/lisp/net/tramp-compat.el
@@ -39,6 +39,7 @@
 (require 'ls-lisp)  ;; Due to `tramp-handle-insert-directory'.
 (require 'parse-time)
 (require 'shell)
+(require 'subr-x)
 
 (declare-function tramp-handle-temporary-file-directory "tramp")
 
@@ -81,7 +82,7 @@ Add the extension of F, if existing."
      ((fboundp 'w32-window-exists-p)
       (tramp-compat-funcall 'w32-window-exists-p process-name process-name))
 
-     ;; GNU Emacs 23.
+     ;; GNU Emacs 23+.
      ((and (fboundp 'list-system-processes) (fboundp 'process-attributes))
       (let (result)
 	(dolist (pid (tramp-compat-funcall 'list-system-processes) result)
@@ -97,10 +98,6 @@ Add the extension of F, if existing."
                                     process-name))))
 	      (setq result t)))))))))
 
-;; `default-toplevel-value' has been declared in Emacs 24.4.
-(unless (fboundp 'default-toplevel-value)
-  (defalias 'default-toplevel-value #'symbol-value))
-
 ;; `file-attribute-*' are introduced in Emacs 25.1.
 
 (defalias 'tramp-compat-file-attribute-type
@@ -306,9 +303,4 @@ A nil value for either argument stands for the current time."
 
 (provide 'tramp-compat)
 
-;;; TODO:
-
-;; * When we get rid of Emacs 24, replace "(mapconcat #'identity" by
-;;   "(string-join".
-
 ;;; tramp-compat.el ends here
diff --git a/lisp/net/tramp-ftp.el b/lisp/net/tramp-ftp.el
index d1aae22a484..2a4fccf57e7 100644
--- a/lisp/net/tramp-ftp.el
+++ b/lisp/net/tramp-ftp.el
@@ -53,8 +53,8 @@ present for backward compatibility."
     (setq file-name-handler-alist
 	  (delete a1 (delete a2 file-name-handler-alist)))))
 
-(eval-after-load "ange-ftp"
-  '(tramp-disable-ange-ftp))
+(with-eval-after-load 'ange-ftp
+  (tramp-disable-ange-ftp))
 
 ;;;###tramp-autoload
 (defun tramp-ftp-enable-ange-ftp ()
diff --git a/lisp/net/tramp-gvfs.el b/lisp/net/tramp-gvfs.el
index cee7a1209bd..e3da20aa88f 100644
--- a/lisp/net/tramp-gvfs.el
+++ b/lisp/net/tramp-gvfs.el
@@ -724,12 +724,7 @@ is no information where to trace the message.")
     (tramp-message tramp-gvfs-dbus-event-vector 6 "%S" event)
     (tramp-error tramp-gvfs-dbus-event-vector 'file-error "%s" (cadr err))))
 
-;; `dbus-event-error-hooks' has been renamed to
-;; `dbus-event-error-functions' in Emacs 24.3.
-(add-hook
- (if (boundp 'dbus-event-error-functions)
-     'dbus-event-error-functions 'dbus-event-error-hooks)
- #'tramp-gvfs-dbus-event-error)
+(add-hook 'dbus-event-error-functions #'tramp-gvfs-dbus-event-error)
 
 
 ;; File name primitives.
@@ -942,7 +937,7 @@ file names."
 	;; Send command.
 	(tramp-gvfs-send-command
 	 v "gvfs-ls" "-h" "-n" "-a"
-	 (mapconcat #'identity tramp-gvfs-file-attributes ",")
+	 (string-join tramp-gvfs-file-attributes ",")
 	 (tramp-gvfs-url-file-name directory))
 	;; Parse output.
 	(with-current-buffer (tramp-get-connection-buffer v)
@@ -1183,7 +1178,7 @@ If FILE-SYSTEM is non-nil, return file system attributes."
 	  (tramp-error
 	   v 'file-notify-error "Monitoring not supported for `%s'" file-name)
 	(tramp-message
-	 v 6 "Run `%s', %S" (mapconcat #'identity (process-command p) " ") p)
+	 v 6 "Run `%s', %S" (string-join (process-command p) " ") p)
 	(process-put p 'vector v)
 	(process-put p 'events events)
 	(process-put p 'watch-name localname)
@@ -1997,15 +1992,12 @@ VEC is used only for traces."
        (list user host)))
    (zeroconf-list-services service)))
 
-;; We use the TRIM argument of `split-string', which exist since Emacs
-;; 24.4.  I mask this for older Emacs versions, there is no harm.
 (defun tramp-gvfs-parse-device-names (service)
   "Return a list of (user host) tuples allowed to access.
 This uses \"avahi-browse\" in case D-Bus is not enabled in Avahi."
   (let ((result
 	 (ignore-errors
-	   (tramp-compat-funcall
-	    'split-string
+	   (split-string
 	    (shell-command-to-string (format "avahi-browse -trkp %s" service))
 	    "[\n\r]+" 'omit "^\\+;.*$"))))
     (delete-dups
@@ -2013,8 +2005,7 @@ This uses \"avahi-browse\" in case D-Bus is not enabled in Avahi."
       (lambda (x)
 	(let* ((list (split-string x ";"))
 	       (host (nth 6 list))
-	       (text (tramp-compat-funcall
-		      'split-string (nth 9 list) "\" \"" 'omit "\""))
+	       (text (split-string (nth 9 list) "\" \"" 'omit "\""))
 	       user)
 	  ;; A user is marked in a TXT field like "u=guest".
 	  (while text
diff --git a/lisp/net/tramp-integration.el b/lisp/net/tramp-integration.el
index 35d2eb38e60..5960871ca7a 100644
--- a/lisp/net/tramp-integration.el
+++ b/lisp/net/tramp-integration.el
@@ -123,18 +123,18 @@ been set up by `rfn-eshadow-setup-minibuffer'."
 	(mapconcat
 	 #'identity (butlast (tramp-compat-exec-path)) path-separator)))
 
-(eval-after-load "esh-util"
-  '(progn
-     (add-hook 'eshell-mode-hook
-	       #'tramp-eshell-directory-change)
-     (add-hook 'eshell-directory-change-hook
-	       #'tramp-eshell-directory-change)
-     (add-hook 'tramp-integration-unload-hook
-	       (lambda ()
-		 (remove-hook 'eshell-mode-hook
-			      #'tramp-eshell-directory-change)
-		 (remove-hook 'eshell-directory-change-hook
-			      #'tramp-eshell-directory-change)))))
+(with-eval-after-load 'esh-util
+  (progn
+    (add-hook 'eshell-mode-hook
+	      #'tramp-eshell-directory-change)
+    (add-hook 'eshell-directory-change-hook
+	      #'tramp-eshell-directory-change)
+    (add-hook 'tramp-integration-unload-hook
+	      (lambda ()
+		(remove-hook 'eshell-mode-hook
+			     #'tramp-eshell-directory-change)
+		(remove-hook 'eshell-directory-change-hook
+			     #'tramp-eshell-directory-change)))))
 
 ;;; Integration of recentf.el:
 
@@ -158,18 +158,18 @@ NAME must be equal to `tramp-current-connection'."
     (let ((recentf-exclude '(file-remote-p)))
       (recentf-cleanup))))
 
-(eval-after-load "recentf"
-  '(progn
-     (add-hook 'tramp-cleanup-connection-hook
-	       #'tramp-recentf-cleanup)
-     (add-hook 'tramp-cleanup-all-connections-hook
-	       #'tramp-recentf-cleanup-all)
-     (add-hook 'tramp-integration-unload-hook
-	       (lambda ()
-		 (remove-hook 'tramp-cleanup-connection-hook
-			      #'tramp-recentf-cleanup)
-		 (remove-hook 'tramp-cleanup-all-connections-hook
-			      #'tramp-recentf-cleanup-all)))))
+(with-eval-after-load 'recentf
+  (progn
+    (add-hook 'tramp-cleanup-connection-hook
+	      #'tramp-recentf-cleanup)
+    (add-hook 'tramp-cleanup-all-connections-hook
+	      #'tramp-recentf-cleanup-all)
+    (add-hook 'tramp-integration-unload-hook
+	      (lambda ()
+		(remove-hook 'tramp-cleanup-connection-hook
+			     #'tramp-recentf-cleanup)
+		(remove-hook 'tramp-cleanup-all-connections-hook
+			     #'tramp-recentf-cleanup-all)))))
 
 ;;; Default connection-local variables for Tramp:
 
@@ -180,16 +180,16 @@ NAME must be equal to `tramp-current-connection'."
 
 ;; `connection-local-set-profile-variables' and
 ;; `connection-local-set-profiles' exists since Emacs 26.1.
-(eval-after-load "shell"
-  '(progn
-     (tramp-compat-funcall
-      'connection-local-set-profile-variables
-      'tramp-connection-local-default-profile
-      tramp-connection-local-default-profile)
-     (tramp-compat-funcall
-      'connection-local-set-profiles
-      `(:application tramp)
-      'tramp-connection-local-default-profile)))
+(with-eval-after-load 'shell
+  (progn
+    (tramp-compat-funcall
+     'connection-local-set-profile-variables
+     'tramp-connection-local-default-profile
+     tramp-connection-local-default-profile)
+    (tramp-compat-funcall
+     'connection-local-set-profiles
+     `(:application tramp)
+     'tramp-connection-local-default-profile)))
 
 (add-hook 'tramp-unload-hook
 	  (lambda () (unload-feature 'tramp-integration 'force)))
diff --git a/lisp/net/tramp-sh.el b/lisp/net/tramp-sh.el
index a42ae9363ca..cee61f15d20 100644
--- a/lisp/net/tramp-sh.el
+++ b/lisp/net/tramp-sh.el
@@ -1135,19 +1135,15 @@ component is used as the target of the symlink."
 		  (setq thisstep (pop steps))
 		  (tramp-message
 		   v 5 "Check %s"
-		   (mapconcat #'identity
-			      (append '("") (reverse result) (list thisstep))
-			      "/"))
+		   (string-join
+		    (append '("") (reverse result) (list thisstep)) "/"))
 		  (setq symlink-target
 			(tramp-compat-file-attribute-type
 			 (file-attributes
 			  (tramp-make-tramp-file-name
 			   v
-			   (mapconcat #'identity
-				      (append '("")
-					      (reverse result)
-					      (list thisstep))
-				      "/")
+			   (string-join
+			    (append '("") (reverse result) (list thisstep)) "/")
 			   'nohop))))
 		  (cond ((string= "." thisstep)
 			 (tramp-message v 5 "Ignoring step `.'"))
@@ -1173,12 +1169,8 @@ component is used as the target of the symlink."
 		   "Maximum number (%d) of symlinks exceeded" numchase-limit))
 		(setq result (reverse result))
 		;; Combine list to form string.
-		(setq result
-		      (if result
-			  (mapconcat #'identity (cons "" result) "/")
-			"/"))
-		(when (string= "" result)
-		  (setq result "/")))))
+		(setq result (if result (string-join (cons "" result) "/") "/"))
+		(when (string-empty-p result) (setq result "/")))))
 
 	  ;; Detect cycle.
 	  (when (and (file-symlink-p filename)
@@ -1993,7 +1985,6 @@ file names."
 	  (t2 (tramp-tramp-file-p newname))
 	  (length (tramp-compat-file-attribute-size
 		   (file-attributes (file-truename filename))))
-	  ;; `file-extended-attributes' exists since Emacs 24.4.
 	  (attributes (and preserve-extended-attributes
 			   (apply #'file-extended-attributes (list filename)))))
 
@@ -2065,7 +2056,6 @@ file names."
 
 	  ;; Handle `preserve-extended-attributes'.  We ignore possible
 	  ;; errors, because ACL strings could be incompatible.
-	  ;; `set-file-extended-attributes' exists since Emacs 24.4.
 	  (when attributes
 	    (ignore-errors
 	      (apply #'set-file-extended-attributes (list newname attributes))))
@@ -2364,7 +2354,7 @@ The method used must be an out-of-band method."
 	       (mapcar
 		(lambda (x)
 		  (setq x (mapcar (lambda (y) (format-spec y spec)) x))
-		  (unless (member "" x) (mapconcat #'identity x " ")))
+		  (unless (member "" x) (string-join x " ")))
 		(tramp-get-method-parameter v 'tramp-copy-env)))
 
 	      remote-copy-program
@@ -3636,8 +3626,8 @@ Fall back to normal file name handler if no Tramp handler exists."
 	  (tramp-error
 	   v 'file-notify-error
 	   "`%s' failed to start on remote host"
-	   (mapconcat #'identity sequence " "))
-	(tramp-message v 6 "Run `%s', %S" (mapconcat #'identity sequence " ") p)
+	   (string-join sequence " "))
+	(tramp-message v 6 "Run `%s', %S" (string-join sequence " ") p)
 	(process-put p 'vector v)
 	;; Needed for process filter.
 	(process-put p 'events events)
@@ -3928,7 +3918,7 @@ This function expects to be in the right *tramp* buffer."
 			   "%s\n%s"))
 		 progname progname progname
 		 tramp-end-of-heredoc
-		 (mapconcat #'identity dirlist "\n")
+		 (string-join dirlist "\n")
 		 tramp-end-of-heredoc))
 	(goto-char (point-max))
 	(when (search-backward "tramp_executable " nil t)
@@ -3946,8 +3936,8 @@ I.e., for each directory in `tramp-remote-path', it is tested
 whether it exists and if so, it is added to the environment
 variable PATH."
   (let ((command
-	 (format "PATH=%s; export PATH"
-		 (mapconcat #'identity (tramp-get-remote-path vec) ":")))
+	 (format
+	  "PATH=%s; export PATH" (string-join (tramp-get-remote-path vec) ":")))
 	(pipe-buf
 	 (or (with-tramp-connection-property vec "pipe-buf"
 	       (tramp-send-command-and-read
@@ -4290,7 +4280,7 @@ process to set up.  VEC specifies the connection."
 		     (append `(,(tramp-get-remote-locale vec))
 			     (copy-sequence tramp-remote-process-environment))))
 	(setq item (split-string item "=" 'omit))
-	(setcdr item (mapconcat #'identity (cdr item) "="))
+	(setcdr item (string-join (cdr item) "="))
 	(if (and (stringp (cdr item)) (not (string-equal (cdr item) "")))
 	    (push (format "%s %s" (car item) (cdr item)) vars)
 	  (push (car item) unset)))
@@ -4300,12 +4290,12 @@ process to set up.  VEC specifies the connection."
 	 (format
 	  "while read var val; do export $var=\"$val\"; done <<'%s'\n%s\n%s"
 	  tramp-end-of-heredoc
-	  (mapconcat #'identity vars "\n")
+	  (string-join vars "\n")
 	  tramp-end-of-heredoc)
 	 t))
       (when unset
 	(tramp-send-command
-	 vec (format "unset %s" (mapconcat #'identity unset " ")) t)))))
+	 vec (format "unset %s" (string-join unset " ")) t)))))
 
 ;; Old text from documentation of tramp-methods:
 ;; Using a uuencode/uudecode inline method is discouraged, please use one
@@ -4873,8 +4863,7 @@ connection if a previous connection has died for some reason."
 		(set-process-query-on-exit-flag p nil)
 		(setq tramp-current-connection (cons vec (current-time)))
 
-		(tramp-message
-		 vec 6 "%s" (mapconcat #'identity (process-command p) " "))
+		(tramp-message vec 6 "%s" (string-join (process-command p) " "))
 
 		;; Check whether process is alive.
 		(tramp-barf-if-no-shell-prompt
@@ -4951,7 +4940,7 @@ connection if a previous connection has died for some reason."
 		       (mapcar
 			(lambda (x)
 			  (setq x (mapcar (lambda (y) (format-spec y spec)) x))
-			  (unless (member "" x) (mapconcat #'identity x " ")))
+			  (unless (member "" x) (string-join x " ")))
 			login-env))
 		      (while login-env
 			(setq command
@@ -4980,7 +4969,7 @@ connection if a previous connection has died for some reason."
 		      (mapconcat
 		       (lambda (x)
 			 (setq x (mapcar (lambda (y) (format-spec y spec)) x))
-			 (unless (member "" x) (mapconcat #'identity x " ")))
+			 (unless (member "" x) (string-join x " ")))
 		       login-args " ")
 		      ;; Local shell could be a Windows COMSPEC.  It
 		      ;; doesn't know the ";" syntax, but we must exit
@@ -5041,7 +5030,7 @@ function waits for output unless NOOUTPUT is set."
       ;; `tramp-echo-mark', so the remote shell sees two consecutive
       ;; trailing line endings and sends two prompts after executing
       ;; the command, which confuses `tramp-wait-for-output'.
-      (when (and (not (string= command ""))
+      (when (and (not (string-empty-p command))
 		 (string-equal (substring command -1) "\n"))
 	(setq command (substring command 0 -1)))
       ;; No need to restore a trailing newline here since `tramp-send-string'
diff --git a/lisp/net/tramp-smb.el b/lisp/net/tramp-smb.el
index 37c40a07f29..695f552b061 100644
--- a/lisp/net/tramp-smb.el
+++ b/lisp/net/tramp-smb.el
@@ -513,7 +513,7 @@ pass to the OPERATION."
 			       tramp-smb-program args)))
 
 		      (tramp-message
-		       v 6 "%s" (mapconcat #'identity (process-command p) " "))
+		       v 6 "%s" (string-join (process-command p) " "))
 		      (process-put p 'vector v)
 		      (process-put p 'adjust-window-size-function #'ignore)
 		      (set-process-query-on-exit-flag p nil)
@@ -774,7 +774,7 @@ PRESERVE-UID-GID and PRESERVE-EXTENDED-ATTRIBUTES are completely ignored."
 			    tramp-smb-acl-program args)))
 
 		    (tramp-message
-		     v 6 "%s" (mapconcat #'identity (process-command p) " "))
+		     v 6 "%s" (string-join (process-command p) " "))
 		    (process-put p 'vector v)
 		    (process-put p 'adjust-window-size-function #'ignore)
 		    (set-process-query-on-exit-flag p nil)
@@ -1258,7 +1258,7 @@ component is used as the target of the symlink."
 	(setq outbuf (current-buffer))))
 
       ;; Construct command.
-      (setq command (mapconcat #'identity (cons program args) " ")
+      (setq command (string-join (cons program args) " ")
 	    command (if input
 			(format
 			 "get-content %s | & %s"
@@ -1425,8 +1425,7 @@ component is used as the target of the symlink."
 			  (tramp-get-connection-buffer v)
 			  tramp-smb-acl-program args)))
 
-		  (tramp-message
-		   v 6 "%s" (mapconcat #'identity (process-command p) " "))
+		  (tramp-message v 6 "%s" (string-join (process-command p) " "))
 		  (process-put p 'vector v)
 		  (process-put p 'adjust-window-size-function #'ignore)
 		  (set-process-query-on-exit-flag p nil)
@@ -1470,7 +1469,7 @@ component is used as the target of the symlink."
 		(get-buffer-create buffer)
 	      ;; BUFFER can be nil.  We use a temporary buffer.
 	      (generate-new-buffer tramp-temp-buffer-name)))
-	   (command (mapconcat #'identity (cons program args) " "))
+	   (command (string-join (cons program args) " "))
 	   (bmp (and (buffer-live-p buffer) (buffer-modified-p buffer)))
 	   (name1 name)
 	   (i 0))
@@ -1965,8 +1964,7 @@ If ARGUMENT is non-nil, use it as argument for
 				   tramp-smb-winexe-program tramp-smb-program)
 			       args))))
 
-	      (tramp-message
-	       vec 6 "%s" (mapconcat #'identity (process-command p) " "))
+	      (tramp-message vec 6 "%s" (string-join (process-command p) " "))
 	      (process-put p 'vector vec)
 	      (process-put p 'adjust-window-size-function #'ignore)
 	      (set-process-query-on-exit-flag p nil)
@@ -2039,8 +2037,8 @@ Removes smb prompt.  Returns nil if an error message has appeared."
 
       ;; Read pending output.
       (while (not (re-search-forward tramp-smb-prompt nil t))
-	(while (tramp-accept-process-output p 0)
-	  (goto-char (point-min))))
+	(while (tramp-accept-process-output p 0))
+	(goto-char (point-min)))
       (tramp-message vec 6 "\n%s" (buffer-string))
 
       ;; Remove prompt.
diff --git a/lisp/net/tramp-sudoedit.el b/lisp/net/tramp-sudoedit.el
index f056e73366e..bbe780099d5 100644
--- a/lisp/net/tramp-sudoedit.el
+++ b/lisp/net/tramp-sudoedit.el
@@ -232,7 +232,6 @@ absolute file names."
 	  (file-times (tramp-compat-file-attribute-modification-time
 		       (file-attributes filename)))
 	  (file-modes (tramp-default-file-modes filename))
-	  ;; `file-extended-attributes' exists since Emacs 24.4.
 	  (attributes (and preserve-extended-attributes
 			   (apply #'file-extended-attributes (list filename))))
 	  (sudoedit-operation
@@ -284,7 +283,6 @@ absolute file names."
 
 	;; Handle `preserve-extended-attributes'.  We ignore possible
 	;; errors, because ACL strings could be incompatible.
-	;; `set-file-extended-attributes' exists since Emacs 24.4.
 	(when attributes
 	  (ignore-errors
 	    (apply #'set-file-extended-attributes (list newname attributes))))
@@ -660,8 +658,7 @@ component is used as the target of the symlink."
   (with-parsed-tramp-file-name (expand-file-name filename) nil
     (when (and (stringp acl-string) (tramp-sudoedit-remote-acl-p v))
       ;; Massage `acl-string'.
-      (setq acl-string
-	    (mapconcat #'identity (split-string acl-string "\n" 'omit) ","))
+      (setq acl-string (string-join (split-string acl-string "\n" 'omit) ","))
       (prog1
 	  (tramp-sudoedit-send-command
 	   v "setfacl" "-m"
@@ -830,7 +827,7 @@ in case of error, t otherwise."
 	   (tramp-verbose (if (= tramp-verbose 3) 2 tramp-verbose))
 	   ;; We do not want to save the password.
 	   auth-source-save-behavior)
-      (tramp-message vec 6 "%s" (mapconcat #'identity (process-command p) " "))
+      (tramp-message vec 6 "%s" (string-join (process-command p) " "))
       ;; Avoid process status message in output buffer.
       (set-process-sentinel p #'ignore)
       (process-put p 'vector vec)
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 3efac8d74f9..90f7491bf51 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -8,7 +8,7 @@
 ;; Keywords: comm, processes
 ;; Package: tramp
 ;; Version: 2.4.2-pre
-;; Package-Requires: ((emacs "24.1"))
+;; Package-Requires: ((emacs "24.4"))
 ;; URL: https://savannah.gnu.org/projects/tramp
 
 ;; This file is part of GNU Emacs.
@@ -572,10 +572,7 @@ This regexp must match both `tramp-initial-end-of-output' and
   :type 'regexp)
 
 (defcustom tramp-password-prompt-regexp
-  (format "^.*\\(%s\\).*:\^@? *"
-	  ;; `password-word-equivalents' has been introduced with Emacs 24.4.
-          (regexp-opt (or (bound-and-true-p password-word-equivalents)
-                          '("password" "passphrase"))))
+  (format "^.*\\(%s\\).*:\^@? *" (regexp-opt password-word-equivalents))
   "Regexp matching password-like prompts.
 The regexp should match at end of buffer.
 
@@ -1862,10 +1859,7 @@ an input event arrives.  The other arguments are passed to `tramp-error'."
 (defun tramp-user-error (vec-or-proc fmt-string &rest arguments)
   "Signal a user error (or \"pilot error\")."
   (unwind-protect
-      (apply
-       #'tramp-error vec-or-proc
-       ;; `user-error' has appeared in Emacs 24.3.
-       (if (fboundp 'user-error) 'user-error 'error) fmt-string arguments)
+      (apply #'tramp-error vec-or-proc 'user-error fmt-string arguments)
     ;; Save exit.
     (when (and tramp-message-show-message
 	       (not (zerop tramp-verbose))
@@ -2103,21 +2097,7 @@ value of `default-file-modes', without execute permissions."
 (defun tramp-replace-environment-variables (filename)
  "Replace environment variables in FILENAME.
 Return the string with the replaced variables."
- (or (ignore-errors
-       ;; Optional arg has been introduced with Emacs 24.4.
-       (tramp-compat-funcall 'substitute-env-vars filename 'only-defined))
-     ;; We need an own implementation.
-     (save-match-data
-       (let ((idx (string-match "\\$\\(\\w+\\)" filename)))
-	 ;; `$' is coded as `$$'.
-	 (when (and idx
-		    (or (zerop idx) (not (eq ?$ (aref filename (1- idx)))))
-		    (getenv (match-string 1 filename)))
-	   (setq filename
-		 (replace-match
-		  (substitute-in-file-name (match-string 0 filename))
-		  t nil filename)))
-	 filename))))
+ (substitute-env-vars filename 'only-defined))
 
 (defun tramp-find-file-name-coding-system-alist (filename tmpname)
   "Like `find-operation-coding-system' for Tramp filenames.
@@ -4149,31 +4129,34 @@ Erase echoed commands if exists."
 Expects the output of PROC to be sent to the current buffer.  Returns
 the string that matched, or nil.  Waits indefinitely if TIMEOUT is
 nil."
-  (with-current-buffer (process-buffer proc)
-    (let ((found (tramp-check-for-regexp proc regexp)))
-      (cond (timeout
-	     (with-timeout (timeout)
-	       (while (not found)
-		 (tramp-accept-process-output proc)
-		 (unless (process-live-p proc)
-		   (tramp-error-with-buffer
-		    nil proc 'file-error "Process has died"))
-		 (setq found (tramp-check-for-regexp proc regexp)))))
-	    (t
+  (let ((found (tramp-check-for-regexp proc regexp)))
+    (cond (timeout
+	   (with-timeout (timeout)
 	     (while (not found)
 	       (tramp-accept-process-output proc)
 	       (unless (process-live-p proc)
 		 (tramp-error-with-buffer
 		  nil proc 'file-error "Process has died"))
 	       (setq found (tramp-check-for-regexp proc regexp)))))
-      (tramp-message proc 6 "\n%s" (buffer-string))
-      (unless found
-	(if timeout
-	    (tramp-error
-	     proc 'file-error "[[Regexp `%s' not found in %d secs]]"
-	     regexp timeout)
-	  (tramp-error proc 'file-error "[[Regexp `%s' not found]]" regexp)))
-      found)))
+	  (t
+	   (while (not found)
+	     (tramp-accept-process-output proc)
+	     (unless (process-live-p proc)
+	       (tramp-error-with-buffer
+		nil proc 'file-error "Process has died"))
+	     (setq found (tramp-check-for-regexp proc regexp)))))
+    ;; The process could have timed out, for example due to session
+    ;; timeout of sudo.  The process buffer does not exist any longer then.
+    (ignore-errors
+      (with-current-buffer (process-buffer proc)
+	(tramp-message proc 6 "\n%s" (buffer-string))))
+    (unless found
+      (if timeout
+	  (tramp-error
+	   proc 'file-error "[[Regexp `%s' not found in %d secs]]"
+	   regexp timeout)
+	(tramp-error proc 'file-error "[[Regexp `%s' not found]]" regexp)))
+    found))
 
 ;; It seems that Tru64 Unix does not like it if long strings are sent
 ;; to it in one go.  (This happens when sending the Perl
@@ -4200,7 +4183,7 @@ the remote host use line-endings as defined in the variable
       (setq string
 	    (mapconcat
 	     #'identity (split-string string "\n") tramp-rsh-end-of-line))
-      (unless (or (string= string "")
+      (unless (or (string-empty-p string)
 		  (string-equal (substring string -1) tramp-rsh-end-of-line))
 	(setq string (concat string tramp-rsh-end-of-line)))
       ;; Send the string.
@@ -4408,12 +4391,10 @@ ID-FORMAT valid values are `string' and `integer'."
   ;; We use key nil for local connection properties.
   (with-tramp-connection-property nil (format "gid-%s" id-format)
     (cond
-     ;; `group-gid' has been introduced with Emacs 24.4.
-     ((and (fboundp 'group-gid) (equal id-format 'integer))
-      (tramp-compat-funcall 'group-gid))
+     ((equal id-format 'integer) (group-gid))
      ;; `group-name' has been introduced with Emacs 27.1.
      ((and (fboundp 'group-name) (equal id-format 'string))
-      (tramp-compat-funcall 'group-name (tramp-compat-funcall 'group-gid)))
+      (tramp-compat-funcall 'group-name (group-gid)))
      ((tramp-compat-file-attribute-group-id
        (file-attributes "~/" id-format))))))
 
@@ -4647,7 +4628,7 @@ are written with verbosity of 6."
 	output error result)
     (tramp-message
      vec 6 "`%s %s' %s %s"
-     program (mapconcat #'identity args " ") infile destination)
+     program (string-join args " ") infile destination)
     (condition-case err
 	(with-temp-buffer
 	  (setq result
@@ -4680,7 +4661,7 @@ are written with verbosity of 6."
 	result)
     (tramp-message
      vec 6 "`%s %s' %s %s %s %s"
-     program (mapconcat #'identity args " ") start end delete buffer)
+     program (string-join args " ") start end delete buffer)
     (condition-case err
 	(progn
 	  (setq result
@@ -4709,7 +4690,7 @@ verbosity of 6."
 	(vec (or vec (car tramp-current-connection)))
 	result)
     (if args
-	(tramp-message vec 6 "%s %s" program (mapconcat #'identity args " "))
+	(tramp-message vec 6 "%s %s" program (string-join args " "))
       (tramp-message vec 6 "%s" program))
     (setq result
 	  (condition-case err
diff --git a/lisp/net/trampver.el b/lisp/net/trampver.el
index 4e1be417a05..79e2b079858 100644
--- a/lisp/net/trampver.el
+++ b/lisp/net/trampver.el
@@ -63,7 +63,7 @@
   "The repository revision of the Tramp sources.")
 
 ;; Check for Emacs version.
-(let ((x   (if (not (string-lessp emacs-version "24.1"))
+(let ((x   (if (not (string-lessp emacs-version "24.4"))
       "ok"
     (format "Tramp 2.4.2-pre is not fit for %s"
             (replace-regexp-in-string "\n" "" (emacs-version))))))